Application of Advanced Material in Offshore Structure.pdf

JADAVPUR UNIVERSITY
Seminar on
Application of Advanced Material in
Offshore Structure
Submitted By- Subhajit Paul
Class Roll No.-002210402004
M.E. in Civil Engineering
Stream- Structural Engineering
Year- 1st Year Second Semester.
Session-2022-23
Under the Guidance of-
Dr. Sreyashi Das (Pal)
(Associate Professor, Department of Civil Engineering)

Certificate
The foregoing Seminar report is hereby approved as a creditable study of
an engineering subject carried out and presented in a manner satisfactory
to warrant its acceptance as a pre-requisite to the degree to Master in
Civil Engineering for which it has been submitted. It is understood that
by this approval the undersigned do not necessarily endorse or approve
any statement made. Opinion expressed or conclusion drawn there, but
approve the report only for the purpose for which it is submitted.
................................
Signature of examiner

Acknowledgement
I would like to express my gratitude to my parents who encouraged my
mathematical and scientific interest from an early age.
I would like to express my gratitude to Dr. Sreyashi Das (Pal) (Associate
Professor, Department of Civil Engineering) for his guidance, academic
encouragement and friendly critique. His attitude and care have helped
me to complete this assignment on time.
I extend my gratitude to Jadavpur University for giving me this
opportunity.
At last but not least gratitude goes to all of my friends who directly or
indirectly helped me to complete this assignment.
.....................................
Subhajit Paul
Roll No.-002210402004
M.E. in Civil Engineering
Stream-Structural Engineering
Jadavpur University
Kolkata-700032

Abstract
Offshore structures face harsh environmental conditions, including corrosive seawater,
high loads, and extreme weather events. The use of advanced materials in offshore
structures has revolutionized their design, construction, and performance. This report
explores the application of advanced materials in offshore structures and highlights
their significant benefits. The report begins by introducing several advanced materials
commonly used in offshore structures. Fiber-reinforced polymers (FRPs), such as
carbon and glass fiber composites, Fiber-reinforced composites and syntactic foams,
offer exceptional strength-to-weight ratios and corrosion resistance. High-strength
steels, titanium alloys, and nickel-based alloys are also discussed, emphasizing their
improved mechanical properties and corrosion resistance. Furthermore, the report
examines the utilization of composite materials in offshore structures. Fiber-
reinforced composites and syntactic foams are explored for their buoyancy, insulation,
and corrosion resistance properties. The incorporation of advanced additives in
concrete, such as microsilica and metakaolin, to improve its strength, durability, and
resistance to chemical attack, is also addressed. The report highlights the benefits of
advanced materials in offshore structures, including enhanced structural integrity,
reduced weight, improved durability, and extended service life. These materials
contribute to increased safety, reduced maintenance costs, and improved operational
efficiency in offshore operations. The use of advanced coatings, such as epoxy and
polyurethane coatings, is also emphasized for their ability to protect offshore
structures from corrosion and fouling. The continuous development of advanced
materials and technologies for offshore structures is a significant area of research and
innovation. The report concludes by emphasizing the ongoing efforts to further
improve the performance and sustainability of offshore structures through the
application of advanced materials. Overall, the integration of advanced materials in
offshore structures is transforming the industry by enabling the construction of more
resilient, cost-effective, and environmentally friendly offshore facilities. The findings
presented in this report underscore the importance of adopting advanced materials in
the design and construction of offshore structures for a safer, more efficient, and
sustainable offshore industry.

Contents
Pgae
1. Introduction-----------------------------------------------------------------------------------1
2. Composite Material-------------------------------------------------------------------------3
2.1. Composite Machining------------------------------------------------------------------3
2.1.1. Fiber Reinforced Composite Materials--------------------------------------------4
2.1.2. Particulate reinforced composite materials----------------------------------------6
2.2. Sandwich-Structured Composite Material-------------------------------------------6
2.2.1. Types of Sandwich-structured Composite----------------------------------------7
2.2.2. Core structure design-----------------------------------------------------------------8
2.2.2.1. Typical core structures-------------------------------------------------------------8
2.2.3. Properties of sandwich structures-------------------------------------------------13
2.2.4. Performance and damage----------------------------------------------------------13
2.2.5. Application in Offshore Structure------------------------------------------------15
2.3. Functionally Graded Material (FGM)----------------------------------------------17
2.3.1. Types of FGMS---------------------------------------------------------------------18
2.3.2. Fabrication Process of FGM-------------------------------------------------------18
2.3.2.1. Vapor Deposition Technique----------------------------------------------------19
2.3.2.2. Powder Metallurgy---------------------------------------------------------------19
2.3.2.3. Centrifugal Casting---------------------------------------------------------------19
2.3.2.4. Solid Freeform Fabrication Method--------------------------------------------19
2.3.3. Properties ----------------------------------------------------------------------------20
2.3.4. Application in Offshore Structure------------------------------------------------21
3. Titanium Alloy------------------------------------------------------------------------------23
3.1. Types of Titanium Alloy-------------------------------------------------------------23
3.2. Properties-------------------------------------------------------------------------------25
3.3. Application in Offshore Structure---------------------------------------------------26
4. High Strength Steel------------------------------------------------------------------------27
4.1. Classification---------------------------------------------------------------------------27
4.2. Characteristics-------------------------------------------------------------------------28
5. Concrete with Advanced Additives-----------------------------------------------------31
5.1. Selected admixtures and additives--------------------------------------------------32
6. Advanced Coatings------------------------------------------------------------------------34
6.1. Types of Offshore Paint--------------------------------------------------------------34
6.2. Coating System------------------------------------------------------------------------37
6.3. Working process of offshore paint--------------------------------------------------38
7. Conclusion-----------------------------------------------------------------------------------40
References--------------------------------------------------------------------------------------42

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Application of Advanced Material in Offshore Structure
1. Introduction
Offshore engineering involves the design, construction, and maintenance of structures
and equipment used in offshore oil and gas exploration, renewable energy
installations, and marine transportation. These structures face numerous challenges
due to the harsh and corrosive marine environment, high loads, and demanding
operational conditions. The application of advanced materials in offshore engineering
has emerged as a promising solution to enhance the performance, durability, and
safety of offshore structures. Advanced materials offer a range of desirable properties
that make them ideal for offshore applications. These materials possess superior
strength, enhanced corrosion resistance, reduced weight, and improved fatigue
properties compared to conventional materials. They also exhibit excellent thermal
stability, erosion resistance, and insulation characteristics, making them highly
suitable for withstanding the demanding offshore conditions.
One of the key areas where advanced materials have made significant contributions in
offshore engineering is the construction of offshore platforms. These platforms are
subjected to immense loads from drilling operations, waves, and currents. Advanced
high-strength steels and fiber-reinforced polymers (FRPs) are extensively used in the
fabrication of offshore platforms to enhance their structural integrity, reduce weight,
and increase load-carrying capacity. Corrosion, caused by exposure to seawater and
harsh chemical environments, is a major concern for offshore structures. Advanced
materials, such as corrosion-resistant alloys like titanium and nickel-based alloys,
have demonstrated superior resistance to corrosion, erosion, and pitting. These
materials find applications in critical components, such as subsea connectors, risers,
and heat exchangers, where corrosion protection is vital.
Furthermore, composite materials have revolutionized the design and construction of
offshore structures. Over the past few decades, composite materials have been very
popular in marine propellers as potential replacement materials. Composite structures
are attractive due to their favorable benefits compared to traditional metal structures,
namely, high strength to weight ratio, superior corrosion resistance, excellent
durability, and high resilience to extreme loads [1]. For highly engineered marine
structures, glass and carbon fiber reinforced composites are manufactured using vinyl
ester or epoxy resins [2]. These laminates can provide excellent performance in the
marine environment with well-selected constituents while being resistant to the
biological and chemical attacks which other materials suffer.
Fiber-reinforced polymers have been widely found in modern engineering fields to act
as structural materials with outstanding mechanical properties and light-weight.
Recently, the environmental-friendly basalt fibers attract more and more attention of
researchers due to their remarkable mechanical performance and low price. Basalt
fiber is a continuous fiber made from natural basalt ore by melting and drawing
through platinum rhodium alloy leakage plate at 1500◦C [3,4]. In addition, its
mechanical properties are better than glass fiber, with high structural strength and
modulus. At the same time, it is much cheaper than carbon fiber without any pollution.

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It has been widely concerned and gradually replaced glass fiber as a substitute for
carbon fiber in infrastructure and civil materials [5–7].
Fiber-composites are one of such innovations that haveimproved the engineering
industry in its processes drastically [8].Fiber-composites have been widely used in the
aeronautical, aerospace and airline industries for their extensive properties of
sturdiness mixed with flimsiness [9]. Electric discharge machiningprocesses and
fabrication are such ways that can help in the cutting and boring processes of these
fiber-composites [10]. These processes if controlled properly can greatly help in the
contouring and shaping of these work pieces as well as giving them proper
shape,shine and luster along as per requirements. In addition to structural materials,
advanced coatings have emerged as an integral part of offshore engineering. These
coatings, such as epoxy and polyurethane coatings, act as protective barriers against
corrosion and fouling, extending the lifespan of offshore structures and minimizing
maintenance requirements. The adoption of advanced materials in offshore
engineering is driven by the need for increased safety, improved efficiency, and
reduced environmental impact. By utilizing these materials, offshore structures can
achieve higher reliability, reduced maintenance costs, and enhanced operational
efficiency. Moreover, the use of advanced materials contributes to sustainable
practices by minimizing material usage, reducing energy consumption, and promoting
environmental stewardship.
In conclusion, the application of advanced materials has revolutionized offshore
engineering by offering superior strength, corrosion resistance, reduced weight, and
improved durability. These materials have found widespread use in offshore platforms,
pipelines, subsea equipment, and protective coatings. Their adoption has significantly
enhanced the safety, reliability, and sustainability of offshore structures, ensuring the
continued growth and success of the offshore industry.
Fig. 1- Offshore Structure

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2. Composite Material
Composite structures are relatively competitive toward conventional materials in
many structure applications, offering a high modulus-to-weight ratio, good damage
tolerance, excellent fatigue strength, and corrosion resistance, providing they can be
worked on to desired forms at an appropriate price and performance. Their biggest
benefit is to be able to offer the necessary characteristics for the choosing and
combination of appropriate reinforcement and matrix properties for a wide variety of
applications. Composite materials are extensively utilized in building, aircraft,
transport, and medical and military applications. Furthermore, the broader use of
composite materials is frequently hampered by the complexity and high expense
involved with their shaping into harmless composite components with the necessary
specifications and surface finishing. Many types of composite materials have
developed in today’s engineering world [11]. These include fibre reinforcing
polymers (FRP), natural fibre composites, metal matrix composites (MMCs) and
ceramic matrix composites (CMC). Composite materials are generally in
homogeneous, anisotropic, and non-ductile.
The fundamental difficulty of machining these materials is the consequent severe
wearing and damage to the sub-surface material. Compositional materials are hard to
machine due to the extreme material’s heterogeneity and anisotropy, its poor thermal
conductivity, thermal sensitivity and rough reinforcement fibre characteristics. In
order to minimize heat production rates and to prevent thermal or mechanical damage,
tool shape, tooling materials, and operating conditions have to be adjusted. Minimum
cutting rates and excessive wear and frequently poor quality of the surface are
encountered This article takes into account non-traditional techniques such as laser
and machine tool cutting. These innovative techniques are utilised in composite
materials to increase cutting speeds, improve surface roughness, or prevent inefficient
conventional procedures [12].
2.1. Composite Machining
According to the concept of composite materials, they are a material system made up
of two or more materials that vary in terms of their chemical and physical
characteristics while being insoluble in each other [13]. The matrix material of a
composite material system is the main component, and it is responsible for load
transmission and structural integrity, while the reinforcing phase assists to the
improvement of the mechanical and tribological features of the structure. Organic
(polymers) or inorganic (ceramic or glass) substances may be used as the matrix and
reinforcing materials, although metallic materials can be used as well (aluminum,
titanium, etc.). Fibers (both long and short) and particles and whisker are the most
frequent types of reinforcing materials used. There is one more phase called the
interfaces, which connects the two stages together and aids in the distribution of load
in an efficient manner. Despite the fact that composite materials are often produced to
be close to net form, machining procedures are frequently required [14]. Composite
materials may be one of the most challenging materials to mill due to their
fundamental homogeneity, abrasive nature of reinforcements, and anisotropic
structure, all of which contribute to significant tool wear and sub-surface damage
during the machining process. However, despite the fact that there is an enormous

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variety of potential pairings in composite materials, this article is mainly concerned
with machining fiber and particulates-based composites [15].
Fig. 2- Types of Composite Materials
2.1.1. Fiber Reinforced Composite Materials
In order to properly machine these composite materials, it is necessary to understand
the characteristics of the fibres and matrix and their impacts on the procedure. In
polymer matrix-based composite systems, reinforcing materials include glass and
carbon fibres, whereas the structure can be either a thermoplastic or thermally-setting
polymer matrix. It has been thoroughly researched experimentally how these fibre-
reinforced polymer matrix composites can be milled and machined [16]. All of these
components cause increased tool wear, which in turn may cause impact phenomena
like fibre pull out, delamination and disbanding. The confrontational nature of the
fibres is responsible for the severe tool wear that occurs with carbon and glass fibre
reinforced composites. Carbon fibre-reinforced polymer (CFRP) composite materials
were subjected to orthogonal machining tests, which measured chip formation,
surface integrity and cutting forces for two fibre orientations: perpendicular and
parallel fibre orientations relative to the focus areas Fibre orientation measurements
had a thick layer than fibre orientation samples, and the chip preparation method was
a sequence of fractures in the fibres [17].
Fig. 3- Fiber Reinforced Composite

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It involves drilling, routing, turning, milling, and water jet cutting of FRP-based
composite materials. A variety of damaging events were discovered while machining
of fibre reinforced composites in this seminal study In the machining of a glass-fibre
reinforced polymer (GFRP), the process of chip production is seen. Chip formation is
strongly reliant on fibre position with relation to the cutting direction. They found
metal-like chips forms when machining composites with the thermoplastic matrix as
compared to thermosetting matrix. As the main wear phenomena identified, fibre
orientation angle and cutting speed were the key players. The carbon fibre was highly
abrasive, which allowed the tool to wear out very quickly. Fibre orientation and feed
were also found to influence surface roughness more than cutting speed. Alignment of
fibres in glass-fibre composites affects cutting forces and fibre pull out (GFRP).
When the tool had a beneficial pitch angle, it caused the smallest level of damages to
the machined composite and produced less cutting force. Additional investigations
also examined the impact on the overall damage found in machined samples by
cutting parameters, work piece material, and fibre orientation [18].
Fig. 4- Various Types of Fibre Reinforced Composite.
Previous studies also confirmed the impact of fibre orientations on the damage: lower
cutting forces for increased fibre orientations leading in less defect. With higher fibre
orientation the cutting force and surface damage increases, but the angle of the ratchet
had little or negligible impact on the cutting forces and damages. Fibre orientation,
tool geometry and machining parameters are factors that contribute mostly to cutting
forces, level of access and work piece material.

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2.1.2. Particulate reinforced composite materials
Machining particulate-reinforced metal matrix composites was widely investigated
scientifically to measure tool wear, surface quality and sub-surface damages that
might occur during the process. Materials, kind, weight percentage and matrix
characteristics, and the arrangement of these pieces in matrix are all variables that
influence the general machinability of these composites. It is thus essential to
correctly choose the equipment and process parameters. In machined of metal matrix
composites, cutting speed, feed and depth of cut have a comparable impact on the life
of the tool and its surface quality as in processing metals, but some variations are
apparent owing to ceramic particles. The ceramic-reinforced particles disturb the
matrix, move before the tool, plug through all the machining surfaces, and generate
patterns [19].
The tool life decreased while the smoothness of the surface only marginally improved
by increasing the cutting speed since the temperatures of the tool rise with the cutting
speed, weakening the tool material and speeding up the wearing of the transmission.
On the other hand, feed adversely affects the roughness of the surface, where the
surface finish starts to deteriorate as feed is increased. The feed also affects the
damage in the sub-surface the most, where enough feed causes more damage and a
higher extent of damage to the substance. That the breakdown of the composite
caused by the cavities caused by strong trimming forces at greater feeds surrounding
the Sic particles. The vacancies come together to produce microscopic cracks and
eventual breaks all along shear strip. Feed, on the other hand, appears to impact tool
wear less[20]. A high feed may decrease the tool wear rate by improving the heat
transfer from the cutting area to the substrate.
Feed increases flank wear, but, only slightly in relation to cutting speed. Cut depth has
a detrimental impact on the finishing and damages to the subsurface. An increasing in
cutting depth reduces the integrity of the surface finish and the damages to the
material. Moreover, the depth of cut is greater than in machining an Al/SiCp/15
percent composite with tungsten carbide unprotected tools for the wearing of
tools[21]. There are several issues with the hard ceramic particulates in the matrix,
particularly the high wear of tools. The best way to use PCD diamond tools is to
choose carbide tools over ceramic tools. PCD tools are preferred to reduce surface
roughness, and surface damage since the wear rate linked with them is the lowest
among the tool available materials. Although PCD tools are utilized for Al/Sic
composites, their high cost restricts their usage.
2.2. Sandwich-Structured Composite Material
In material science, a sandwich-structured composite is a special class of composite
materials that is fabricated by attaching two thin-but-stiff skins to a lightweight but
thick core. The core material is normally low strength, but its higher thickness
provides the sandwich composite with high bending stiffness with overall low density.
Structured foams like polyethersulfone, polyvinylchloride, polyurethane, polyethylene
or polystyrene foams, balsa wood, syntactic foams, and honeycombs are commonly
used core materials. Sometimes, the honeycomb structure is filled with other foams
for added strength. Open- and closed-cell metal foam can also be used as core

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materials. Laminates of glass or carbon fiber-reinforced thermoplastics or
mainly thermoset polymers (unsaturated polyesters, epoxies...) are widely used as skin
materials. Sheet metal is also used as skin material in some cases. The core is bonded
to the skins with an adhesive or with metal components by brazing together.
2.2.1. Types of Sandwich-structured Composite
Metal composite material (MCM) is a type of sandwich formed from two thin skins of
metal bonded to a plastic core in a continuous process under controlled pressure, heat,
and tension.[22]
Recycled paper is also now being used over a closed-cell recycled kraft honeycomb
core, creating a lightweight, strong, and fully repulpable composite board. This
material is being used for applications including point-of-purchase displays,
bulkheads, recyclable office furniture, exhibition stands, wall dividers and terrace
boards.[23]
To fix different panels, among other solutions, a transition zone is normally used,
which is a gradual reduction of the core height, until the two fiber skins are in touch.
In this place, the fixation can be made by means of bolts, rivets, or adhesive.
With respect to the core type and the way the core supports the skins, sandwich
structures can be divided into the following groups: homogeneously supported,
locally supported, regionally supported, unidirectionally supported, bidirectionally
supported.[24] The latter group is represented by honeycomb structure which, due to
an optimal performance-to-weight ratio, is typically used in most demanding
applications including aerospace.
Fig. 5- Sandwich-Structured Composite

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2.2.2. Core structure design
Structure design is the first step of sandwich structure creative design. Sandwich
structure can be typically classified as honeycomb, foam, corrugated, and truss core
sandwich structures according to different core structures. The categorization of
sandwich structure is summarized in Fig. 6 and is discussed in detail below.
Fig. 6-Categorization of sandwich structures.
2.2.2.1. Typical core structures
Truss cores, foam cores, corrugated cores, and honeycomb cores are typical core
structures. Fig. 6 shows some typical sandwich structures. Among them, honeycomb
cores, corrugated cores, and truss core are periodically repeated inner structures.
Compared with foam, more empty volume is formed in the core region with
periodically repeated inner structures. As shown in Fig. 7, corrugated cores typically

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have open channels in one direction. Opposed to corrugated cores, honeycomb cores
are usually closed-cell structure, such as hexagonal honeycomb cores, square
honeycomb cores, and square honeycomb cores.
Fig. 7- Typical sandwich structures: (a) pyramidal truss, (b) square honeycomb, (c) foam
core, and (d) triangular corrugated sheet.

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Fig. 8 - Illustrations for four types of honey tubes: (a) Sq_symtube, (b) Sq_udtube, (c)
Kag_udtube, and (d) Tri_udtube, with (i) 3D view, (ii) top view, and (iii) representative unit
cell of these honey tubes structures. 3D: three-dimensional.

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Fig. 9 - honeycomb core structures: (a) honeycomb, (b) reentrant auxetic, (c) auxetic-strut,
(d) auxetic-honeycomb1 (AH-V1), and (e) auxetic-honeycomb2 (AH-V2).

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Fig. 10 - Schematic of stitched foam sandwich panels: (a) stitched foam core with oblique
direction, (b) stitched foam core with vertical direction, (c) X-core foam core, and (d) K-core
foam core.
Fig. 11- Core Material.

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2.2.3. Properties of sandwich structures
The strength of the composite material is dependent largely on two factors:
 The outer skins: If the sandwich is supported on both sides, and then stressed by
means of a downward force in the middle of the beam, then the bending moment
will introduce shear forces in the material. The shear forces result in the bottom
skin in tension and the top skin in compression. The core material spaces these
two skins apart. The thicker the core material the stronger the composite. This
principle works in much the same way as an I-beam does [25].
 The interface between the core and the skin: Because the shear stresses in the
composite material change rapidly between the core and the skin, the adhesive
layer also sees some degree of shear force. If the adhesive bond between the two
layers is too weak, the most probable result will be delamination. The failure of
the interface between the skin and core is critical and the most common damage
mode. The propensity of this damage to propagate through the interface or dive
either into the skin or core is governed by the shear component [26].
2.2.4. Performance and damage
Performance
Multifunctional characteristics and excellent mechanical properties can be obtained
due to low-density core structure and two high-performance thin facing sheets. The
performance of sandwich panels strongly depends on geometric configuration of the
core and the mechanical properties of face and core materials. In the past few years,
extensive research studies have been carried out to study the energy absorption,
ballistic resistance, heat dissipation, and acoustic absorption capabilities of sandwich
panels.
Energy absorption
Energy absorption is one of the most common characteristics of sandwich structures
[27-34]. Zhang et al.[35] proposed a MSC by incorporating the advantages of
different corrugated cells. It is found that graded sinusoidal corrugated configuration
has excellent energy absorption capacity. Ajdari et al.[36] studied the dynamic
crushing and energy absorption behavior of 2D honeycombs with regular, irregular,
and functionally graded arrangements. At early stages of crushing, decreasing the
relative density in the direction of crushing was shown to enhance the energy
absorption of honeycombs.[36] Aluminum honeycomb cores in various geometries
are suitable core structures for energy absorption when susceptible to low speed
impacts.[37] Increased shear strength of titanium honeycomb cores has been
demonstrated when compared to equivalent density aluminum honeycomb materials.
Basis function network with response surface method was applied to optimize the
shape of truss core panel for superior energy absorption ability.[38] Yan et al.[39]
investigated the compressive strength and energy absorption of sandwich panels with
aluminum foam-filled corrugated cores. The foam-filled corrugated panels were found
to have better energy absorption ability than empty corrugate panels and the foam
alone.[38] Kagome structures are similar to rod-like internal structures of cancellous
bone and have been identified as a near-ideal lattice configuration for exceptional
strength properties. Composite materials are widely used in sandwich structures due

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to lightweight and good mechanical performance. Biological materials such as bio
coconut are chosen as core material in the study of Kong et al.[40] and shown
excellent crashworthiness performance.
Ballistic resistance
Moreover, the ballistic resistance performance of sandwich structures has been
studied for a wide range of applications.[41,42] Ni et al. [43] investigated the ballistic
resistance of three different types of hybrid-cored sandwich structure. Sandwich
panels having metallic pyramidal lattice trusses with ceramic prism insertions and
void-filling epoxy resin were demonstrated better ballistic resistance performance
than the other two types. It is found that the back-sheet is more important than the
front face-sheet in resistance ballistic impacts. Imbalzano et al. [44] compared the
ballistic resistance performance of equivalent sandwich panels composed of auxetic
and conventional honeycomb cores and metal facets. Auxetic panels demonstrated
enhanced ballistic resistance by progressively drawing material into the locally loaded
zone which lead to better crushing behavior.
Heat dissipation
Sandwich structures can be used as thermal protection system structures due to their
heat dissipation characteristic and load-bearing ability. Ceramic matrix composites
such as C/C composite, C/SiC composite, and C/C-SiC composite have outstanding
combined properties of high temperature resistance, oxidation resistance, corrosion
resistance and low density, and low thermal conductivity. Li et al. [45] developed the
equivalent thermal conductivity prediction method for the C/SiC composite
corrugated core sandwich plane. Zhou et al. [46] conducted thermal-mechanical
optimization of V-pattern folded core sandwich panels for thermal protection systems.
Zhou et al. [47] developed an improved analytical rule of mixtures approach for
calculating thermal conductivity considering shape of M-pattern folded core with
Inconel 718 top-face sheet, Ti-6Al-4V titanium alloy folded core, and aluminum 2024
alloy are bottom-face sheet.
Acoustic absorption
In addition to the mentioned multifunctional abilities, the acoustic absorption
performance of sandwich structures has also been investigated in recent years. Li and
Yang [48] presented shape optimization designs for maximum sound transmission
loss (STL) of the sandwich panels with cellular core. The STL of presented sandwich
panels can be changed by adjusting their hybrid cellular core configurations. Wang
and Ma [49] investigated the STL through sandwich structure with pyramidal truss
cores immersed in the surrounding acoustic fluids. Generally, the sound insulation
property of sandwich structures turns better with the increase of compactness of the
structure.
Damage
Sandwich structures can damage in several ways, such as tension or compression
failure of facings, [45,50,51-54] shear failure of the core, [50] wrinkling failure of the
compression facing, [55] de-bonding of the core-facing interface, [45,56] local

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indentation, [57] and global bucking.[53] Load type, structure material properties, and
geometrical construction can influence the failure modes in the aspect of initiation,
propagation, and interaction. Xu et al. [57] summarized four possible failure modes in
three-point bending of the graded lattice core sandwich structure, including face
crushing, face wrinkling, CSF, and indentation failure. The collapse load can be
calculated according to different failure mode. Wang et al.[53] found two main kinds
of compressive failure of X-type lattice core sandwich structure including structure
fracture (large relative density) and structure bucking (small relative density) which
are caused by axial force. There are one more modes corresponding to shear failure
namely face-core de-bonding. Yang et al. [56] introduced four structure defects
including face-truss de-bonding, truss missing, face sheet wrinkling, and gap
reinforcing to study the dynamic behavior of pyramidal truss-like core sandwich
cylinder panels. Hu et al. [58] observed a coupled compression-shear mode in the
compression of corrugated lattice truss composite sandwich panels. Failure maps
[53] were conducted for different sandwich structures by deriving analytical closed-
form expressions for strength for all possible failure modes under each loading.
2.2.5. Application in Offshore Structure
Sandwich-structure composite materials have several advantageous applications in
offshore structures due to their unique combination of high strength, low weight, and
superior mechanical properties. These materials typically consist of a lightweight core
sandwiched between two strong face sheets. Here are some key applications of
sandwich-structure composite materials in offshore engineering:
Offshore Platforms and Topsides
Sandwich composites can be utilized in the construction of topside modules and deck
structures of offshore platforms. The lightweight core provides excellent stiffness and
rigidity, while the face sheets offer impact resistance and protection against
environmental factors.
Floating Production Systems
Sandwich composites are well-suited for use in the construction of floating production
systems, such as floating production storage and offloading (FPSO) vessels. The low
weight of the composite material contributes to buoyancy, reducing the overall
displacement and allowing for increased payload capacity.
Nacelles and Blades for Offshore Wind Turbines
In offshore wind energy applications, sandwich composites are commonly employed
in the construction of wind turbine nacelles and blades. The lightweight core enhances
aerodynamic efficiency, while the face sheets provide structural integrity and
protection against harsh marine conditions.

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Subsea Equipment and Structures
Sandwich composites can be used in the design of subsea equipment, such as subsea
umbilicals, risers, and flowlines. Their high strength-to-weight ratio and corrosion
resistance make them ideal for withstanding the subsea environment.
Boat Hulls and Marine Vessels
Sandwich composites find applications in the construction of boat hulls and marine
vessels used in offshore operations. The lightweight nature of these materials
contributes to fuel efficiency and increased payload capacity.
Helidecks and Helipads
Offshore platforms and structures with helidecks or helipads often use sandwich
composites due to their high strength and low weight. These materials provide
structural stability for safe helicopter landings and takeoffs.
Piping Systems and Pipe Supports
Sandwich-structure composite materials can be employed in offshore piping systems
and pipe supports to reduce weight and enhance mechanical performance.
Buoyancy Modules
Sandwich composites are commonly used to construct buoyancy modules for offshore
structures, providing buoyancy support and load-carrying capabilities.
Subsea Pipe Insulation
The lightweight and insulating properties of sandwich composites make them suitable
for use in subsea pipe insulation systems to maintain the temperature of transported
fluids.
Underwater Acoustic Equipment
Sandwich composites can be used in the construction of underwater acoustic
equipment, such as sonar domes and acoustic reflectors, due to their excellent acoustic
properties.
The versatility and performance characteristics of sandwich-structure composite
materials make them attractive for various offshore applications. However, it's
essential to consider factors such as material compatibility, manufacturing techniques,
and environmental durability when incorporating these materials into offshore
structures. With ongoing advancements in composite technology, the application of
sandwich composites in the offshore industry is likely to continue growing, driving
innovation and improving the efficiency and sustainability of offshore operations.

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2.3. Functionally Graded Material (FGM)
Functionally graded materials (FGM) are useful in the Defence, aerospace, and
medical field; recent attempts are made to assess their use in the marine environment
[59]. Process industries where pipelines are subjected to corrosion under chlorides and
sulphides, many mechanical components and appurtenances are replaced with FGM
[60]. FGM is a novel material manufactured by functionally-grading two metal
components, which are chosen based on strength and corrosion resistance.
Manufacturing such materials is a big challenge as the manufacturing process shall
impose significant challenges in achieving the desired properties of FGM [61]. In the
manufacturing process of FGM, materials of desired characteristics are chosen, and
their geometric compositions (not the metallurgical composition), in terms of
thickness and number of layers, are varied continuously across the cross-section. Thus,
the composition and microstructure are altered along the cross-section to generate the
desired property gradient. It is intended to utilise completely the mechanical,
metallurgical and structural properties of the original materials while forming the
FGM [62]. The wire arc additive manufacturing method (WAAM) enables the
metallurgical composition of user-defined materials by a step-wise addition [63]. The
component metals are deposited in layers in wires, while an electric arc is used as the
heat source. Metallic wires are advanced using a secondary wire-feeder at the desired
speed. A high-pulse current is supplied to form an arc between the electrode wires and
the substrate, resulting in the melting of the filler tip of these advancing wires. A
stainless-steel substrate is used to deposit the materials, while a high- power source is
used for the deposition process. Figure 12 shows various components of the WAAM
unit, namely the Cold Metal Transfer (CMT) torch, the substrate and the CNC
machine integrated with the torch. The deposition parameters for the WAAM process
are based on the constituent materials and the appropriate fillers.
Fig. 12-WAAM unit used to manufacture FGM

18
2.3.1. Types of FGMS
Depending upon the nature of gradient, the functionally graded materials (composites)
may be grouped into following types -
1. Fraction gradient type (Fig. 13a)
2. Shape gradient type (Fig.13b)
3. Orientation gradient type (Fig.13c)
4. Size (of material) gradient type
Fig. 13- Different types of functionally graded composites. Gradient of: (a) fraction, (b)
shape, (c) orientation, and (d) size gradient type.
2.3.2. Fabrication Process of FGM
The fabrication process is one of the most crucial fields in FGM research. A number
of research papers have been published till to date on the process techniques of FGM
yielding new methods of FGM manufacturing. Based on constructive processing and
mass transport processing techniques, FGM can be divided into two major categories
[64]. In constructive processing, the FGM is made layer by layer starting with an

19
appropriate distribution in which the gradients are literally fabricated in space, while
in mass transport, the gradients within a component are dependent on natural transport
phenomena, such as heat conduction, diffusion of atomic species, and flow of fluid
[65]. However, advancement in automation technology in the past two decades has
made constitutive gradation process both technically and economically more feasible.
2.3.2.1. Vapor Deposition Technique
A number of vapor deposition techniques are now adopted by manufacturers
including sputter deposition, chemical vapor deposition, physical vapor deposition,
plasma-enhanced chemical vapor deposition, and so on. Using the vapor deposition
method, the material is used to condense in a vapor phase through chemical reaction,
condensation, or conversion to form a solid material [64]. The aforementioned
techniques are fruitful to change the material properties like electrical, mechanical,
optical, and thermal. Using these methods, the functionally graded surface coatings
are deposited which in turn can supply marvelous microstructure for thin surface
coatings. Using vapor deposition techniques, poisonous gases are yielded as a by-
product [66].
2.3.2.2. Powder Metallurgy
Four steps are involved in powder metallurgy for the production of functionally
graded materials [67-69]. These are powder preparation, weighting and mixing of
powder, stacking and ramming of premixed powders, and finally sintering [70]. A
number of methods are used for preparation of powder like chemical reaction,
electrolytic deposition, atomization, solid state reduction, centrifugal disintegration,
grinding, pulverization, etc. The forming process includes compacting of powder into
geometric form, and pressing is usually completed in a room temperature [66].
Compatibility insured the strength of pressed and unsintered part [70]. The sintered
part is usually made without a particular structure. During the process, some pores
may occur which can be removed from secondary process [65].
2.3.2.3. Centrifugal Casting
In the centrifugal casting method, the functionally graded material is produced by
spinning the mold using gravitational force. Metal in molten state is used to put into
spinning mold, and it continues to spin until the metal becomes solidified [65].
Cylindrical parts are usually made through this method. Using this method, the
density of metal increased and the mechanical properties of the casting may increase
by 10 to 15% [71]. Difference in the centrifugal force which is produced by the
density difference in molten and solid particles creates compositional gradient in
FGM [72,73]. From the literature review, it was found that there is limitation on
gradient due to its production of natural process (i.e., centrifugal force and density
difference).
2.3.2.4. Solid Freeform Fabrication Method
The solid freeform fabrication method is one of the most adapted methods for the
production of physical shapes with the help of computer-generated information about

20
the object [65]. This method has an ability to vary the internal composition of
materials [74,75]. This method has many advantages over the other methods such as
less energy consumption, higher manufacturing speed, efficient utilization of material,
and being capable of producing complex shapes and design [74]. In the solid freeform
fabrication method, the laser-based process is widely used for the fabrication of FGM
[66].
2.3.3. Properties
Functionally Graded Materials (FGMs) have gained increasing attention in the design
and construction of offshore structures due to their unique properties and potential
benefits. FGMs are composite materials that exhibit a gradual variation in
composition, microstructure, or properties over their volume. In the context of
offshore structures, the composition and properties of FGMs are tailored to meet
specific performance requirements under various environmental and operational
conditions.
The use of FGMs in offshore structures offers several advantages:
Mechanical Properties
FGMs can be designed to have a gradual transition of mechanical properties, such as
stiffness and strength, from one surface to another. For instance, an offshore platform
may require higher strength and stiffness at its base to withstand the weight and loads,
while having increased flexibility and toughness towards the top to accommodate
dynamic forces like waves and wind.
Stress Mitigation
Offshore structures are subjected to various types of loads, including static, dynamic,
and cyclic loads. FGMs can be designed to have a gradual variation in stiffness and
strength properties, allowing for effective stress distribution and mitigation. This
property helps reduce stress concentration and potential failure points, improving the
structural integrity and fatigue resistance of offshore components.
Corrosion Protection
Corrosion is a significant concern in offshore environments due to exposure to
seawater and aggressive chemicals. Functionally graded materials can be designed to
have a corrosion-resistant layer on the surface, gradually transitioning to a structurally
strong material in the core. This approach provides improved corrosion protection
without compromising the mechanical properties of the offshore structure.
Weight Optimization
Offshore structures often require lightweight materials to minimize the overall weight
and reduce installation and transportation costs. Functionally graded materials can be
designed to have a gradual variation in density, allowing for weight reduction while
maintaining structural integrity. This weight optimization can be particularly
beneficial in applications such as risers, subsea equipment, and floating platforms.

21
Thermal Management
Offshore structures are exposed to significant temperature variations, especially in
deep-water environments. Functionally graded materials can be engineered to have a
gradual variation in thermal conductivity, enabling effective thermal management.
This property helps regulate temperature differentials, minimize thermal stresses, and
enhance the performance of offshore components.
Material Compatibility
Offshore structures often require the joining of different materials with varying
properties. Functionally graded materials can provide a seamless transition between
different materials, enabling efficient bonding and reducing the risk of interfacial
failures. This compatibility facilitates the integration of dissimilar materials,
optimizing the design and performance of offshore structures.
Reduced Material Usage
FGMs allow for the design of components with varying material properties in a single
structure. This design flexibility reduces the overall material usage, resulting in cost
savings and improved sustainability in offshore engineering.
While functionally graded materials offer numerous advantages, their design,
fabrication, and implementation present technical challenges. Developing suitable
manufacturing techniques, characterizing material properties, and ensuring structural
integrity are ongoing areas of research.
In conclusion, functionally graded materials have the potential to revolutionize the
design and performance of offshore structures. Their ability to provide tailored
properties, stress mitigation, corrosion protection, weight optimization, thermal
management, material compatibility, and reduced material usage makes them highly
valuable in offshore engineering. Continued research and development in this field
will unlock further opportunities for utilizing functionally graded materials to enhance
the efficiency, safety, and sustainability of offshore structures.
2.3.4. Application in Offshore Structure
Functionally graded materials (FGMs) have several promising applications in
offshore structures, where their tailored properties can enhance performance,
durability, and safety. Some of the key applications of functionally graded materials
in offshore engineering include:
Subsea Pipelines
FGMs can be employed in the construction of subsea pipelines, where they can offer a
gradual transition of properties from the outer layer, providing enhanced corrosion
resistance, to the inner layer, offering improved mechanical strength. This property
helps to protect the pipeline from corrosive seawater while maintaining structural
integrity under high-pressure conditions.

22
Subsea Connectors and Joints
FGMs can be employed in subsea connectors and joints to provide a gradual transition
of material properties, optimizing the stress distribution and enhancing the
performance and reliability of these critical connections.
Subsea Equipment
Functionally graded materials can be utilized in the construction of subsea equipment,
such as valves, pumps, and heat exchangers, offering enhanced corrosion resistance in
the outer layer and improved mechanical properties in the inner layer.
Thermal Management Systems
FGMs can be employed in heat exchangers and thermal management systems for
offshore structures to optimize heat transfer efficiency by controlling the thermal
conductivity of the material.
Floating Platforms
FGMs can find application in the construction of floating platforms, such as floating
production storage and offloading (FPSO) vessels. The gradual variation of properties
can optimize the platform's structural response to wave loads and improve overall
stability.
Seabed Foundations
Functionally graded materials can be utilized in seabed foundations for offshore
structures, offering tailored mechanical properties to adapt to the varying soil
conditions and loading profiles.
Offshore Wind Turbines
In offshore wind energy applications, FGMs can be used in various components, such
as turbine blades, towers, and foundation structures. The tailored properties can
optimize the mechanical response to wind loads and improve overall turbine
efficiency and lifespan.
Offshore Platforms
Functionally graded materials can be used in the fabrication of offshore platform
components, such as risers, columns, and braces. By designing FGMs with varying
mechanical properties, the material can be tailored to withstand different loads and
environmental conditions experienced by different sections of the platform.
Riser Systems
FGMs can find application in riser systems, which connect subsea wells to floating
platforms. The graded material properties can optimize stress distribution, reduce

23
weight, and enhance fatigue resistance in these critical components, improving the
overall reliability of riser systems.
Buoyancy Modules
Functionally graded materials can be utilized in buoyancy modules for offshore
structures, offering a smooth variation in density from the surface to the core. This
feature allows for efficient buoyancy while minimizing the weight and volume of the
modules.
By incorporating functionally graded materials into offshore structures, engineers can
benefit from improved structural performance, reduced weight, enhanced corrosion
resistance, and optimized stress distribution. However it is important to note that the
application of functionally graded materials in offshore structures is an area of
ongoing research and development. As new advancements emerge, FGMs have the
potential to further optimize offshore operations, enhance safety, and improve the
overall performance and longevity of offshore structures.
3. Titanium Alloy
For marine engineering materials, it is required to have high strength, resistance to
corrosion of hydrothermal fluids, anti-vulcanization, anti-microbial adhesion and high
toughness. The titanium metal is called "Ocean Metal" because of its excellent
lightweight, high strength and corrosion resistance, especially its ability to resist the
erosion of saltwater or seawater and marine atmospheric environment. Titanium is
widely used in marine engineering, especially suitable for light, marine equipment. It
is one of the new key materials in the marine engineering field.
3.1. Types of Titanium Alloy
Depending on the metallurgical structure, Titanium alloys can be classified into three
broad categories [76] as listed below:
Alpha Alloys
It is alloyed with small amounts of oxygen to enhance commercially pure titanium’s
hardness and tensile strength. It is feasible to manufacture a range of economically
pure titanium grades with strength values ranging from 290 to 740 MPa by adjusting
the amounts added.
Although minor amounts of beta phase are possible if the impurity levels of beta
stabilizers such as iron are significant, these materials are nominally completely alpha
in structure. While the alpha alloys cannot be heat-treated to increase strength, adding
2.5 percent copper to titanium produces a material that responds to solution treatment
and aging the same way that aluminum-copper alloys do. Aluminum is an alpha
stabilizer found in several commercially available alloys as an alloying additive to
titanium.

24
Alpha-Beta Alloys
The beta phase is stabilized by vanadium, molybdenum, iron, and chromium, and
various alpha-beta alloys have been created. These are typically medium to high-
strength materials, with tensile strengths ranging from 620 to 1250 MPa and creep
resistance ranging from 350 to 400°C. Low and high cycle fatigue and fracture
toughness are increasingly important to design characteristics. Thus,
thermomechanical and heat treatment processes have been developed to ensure that
the alloys provide the best mechanical properties for various applications. Near alpha,
alloys are employed for maximal creep resistance at temperatures above 450°C. At
temperatures up to 600°C, they have sufficient creep strength.
Beta Alloys
Beta alloys are the other type of titanium substance. All-beta alloys can be made when
enough beta-stabilizing elements are added to titanium. These materials have been
around for a long time but have only recently gained popularity. They’re easier to
hard work than alpha-beta alloys, can be heat treated to high strengths, and some have
better corrosion resistance than commercially pure grades. There are international and
national specifications for titanium materials used in aerospace, but none exist for
materials used in non-aerospace applications. The ASTM collection of specifications
is commonly utilized in this industry.
Fig. 14- α-β phase transformations in titanium alloys, a) α phase crystal structure, b) β phase
crystal structure, c) Phase transformation mechanism

25
Fig. 15- Martensitic transformation curve of titanium alloys
3.2. Properties
Titanium alloys possess several properties that make them suitable for offshore
structures. When used in the construction of offshore components, titanium alloys
offer the following key properties:
Corrosion Resistance
Titanium alloys exhibit exceptional corrosion resistance, particularly in seawater and
aggressive environments. They form a protective oxide layer on the surface that helps
prevent corrosion and degradation, making them well-suited for offshore structures
exposed to corrosive conditions.
High Strength-to-Weight Ratio
Titanium alloys have a remarkable strength-to-weight ratio, comparable to high-
strength steels but with a significantly lower density. This property allows for the
construction of lightweight offshore components without compromising structural
integrity or load-carrying capacity. The high strength-to-weight ratio is advantageous
in weight-sensitive offshore applications, such as platforms and subsea equipment.
High Specific Strength
Titanium alloys offer high strength relative to their weight. This property enables the
fabrication of offshore components that can withstand significant loads and stresses

26
while keeping the overall weight of the structure low. It contributes to improved
performance, reduced structural fatigue, and increased payload capacity in offshore
operations.
Excellent Fatigue Strength
Titanium alloys demonstrate excellent fatigue strength, allowing them to withstand
cyclic loading and prolonged exposure to dynamic stresses. This property is vital in
offshore structures subjected to waves, currents, and varying loads, as it ensures the
long-term durability and reliability of the components.
Low Thermal Expansion
Titanium alloys have a relatively low coefficient of thermal expansion, providing
dimensional stability under varying temperature conditions. This property is
advantageous in offshore structures where temperature fluctuations are common, as it
helps prevent issues such as thermal stress and distortion.
Non-Magnetic Property
Titanium alloys are non-magnetic, which is advantageous in offshore structures that
require minimal magnetic interference. This property helps avoid disruptions to
sensitive equipment or instruments that may be affected by magnetic fields.
Good Weldability
Titanium alloys exhibit good weldability, allowing for ease of fabrication and
assembly during the construction of offshore structures. Proper welding techniques
and procedures are essential to ensure strong and reliable joints in titanium alloy
components.
Biocompatibility
Titanium alloys are biocompatible, meaning they are well-tolerated by the human
body and have low toxicity. This property is valuable in offshore medical and
underwater research applications, where titanium alloys can be safely used in contact
with human tissue or marine organisms.
While titanium alloys possess these desirable properties, it's important to consider
their higher cost compared to conventional materials. Engineers and designers
carefully evaluate the specific requirements, performance needs, and cost-
effectiveness of titanium alloys to determine their optimal use in offshore structures.
3.3. Application in Offshore Structure
Offshore Subsea Components
Titanium alloys are used in subsea components, such as connectors, manifolds, and
valves, where corrosion resistance and lightweight properties are crucial.

27
Seawater Intake Systems
Titanium alloys are employed in seawater intake systems, where their corrosion
resistance is vital to ensure continuous operation and minimize maintenance
requirements.
Marine Heat Exchangers
Titanium heat exchangers are utilized in offshore platforms for their excellent
corrosion resistance and thermal performance.
Subsea Wellhead Systems
Titanium alloys can be used in subsea wellhead systems to enhance corrosion
resistance and withstand harsh subsea conditions.
Riser Systems
Titanium alloy risers are employed to provide corrosion resistance and weight
reduction, ensuring efficient drilling and production operations.
While titanium alloys offer numerous advantages, their high cost remains a limiting
factor in their widespread adoption in offshore structures. Engineers and designers
carefully evaluate the specific requirements of each project to determine where the
benefits of titanium alloys justify their use over more cost-effective materials. As
research and technology advancements continue, the application of titanium alloys in
offshore structures may expand, leading to further innovations in the offshore industry.
4. High Strength Steel
The requirements on structural steel plates for offshore structures differ because of the
varying fields of application and location. Today, there are four major standards
existing, beside of the shipbuilding standards, which describe the severe requirements
on structural steel plates for offshore constructions.
Steelmakers have developed and improved new processes for making low-carbon,
low-impurity, high-strength steel plates with high toughness and improved weld
ability at low cost [79].
High strength steels, defined as steels with minimum yield strengths of 450 MPa, are
widely used in jack-up construction and are being used increasingly in the fabrication
of fixed offshore structures [80].
4.1. Classification
High-strength structural steels for offshore fabrication can be generally classified as
follows:
 Carbon steel (carbon-manganese) heat treated for enhanced properties
 Low-alloy, high-strength steel (probably heat-treated)
 Precipitation-hardening steel (A710) (probably heat-treated)

28
4.2. Characteristics
High-strength steel is a vital material used extensively in the construction of offshore
structures. Its exceptional mechanical properties and specific advantages make it an
ideal choice for various applications in the offshore industry. Some key characteristics
and uses of high-strength steel in offshore structures include:
High Yield Strength
High-strength steel possesses significantly higher yield strength than conventional
mild steel. This property allows for the design of lighter, more slender structural
elements that can carry substantial loads and resist deformation.
Excellent Toughness
High-strength steel exhibits excellent toughness, enabling it to absorb energy and
resist crack propagation. This toughness is crucial in offshore structures, as it
enhances their ability to withstand dynamic loading, impact, and extreme
environmental conditions.
Corrosion Resistance
High-strength steels are often alloyed with elements like chromium, nickel, and
molybdenum to enhance their corrosion resistance. This property is essential in
offshore structures exposed to harsh marine environments, reducing the risk of
corrosion-related failures and extending the lifespan of the components.
(a)

29
(b)
Fig. 16 (a), (b)- Corrosion resistant epoxy coated high strength steel
Fatigue Resistance
The combination of high yield strength and excellent toughness in high-strength steel
results in superior fatigue resistance. Offshore structures, subject to cyclic loads from
waves, currents, and operational activities, benefit from the material's ability to
withstand repeated stress cycles without failure.
Reduced Material Usage
The high strength of the steel allows for the design of lighter, more slender
components, leading to reduced material consumption. This not only lowers
construction costs but also facilitates easier transportation and installation of offshore
structures.
Increased Load-Carrying Capacity
High-strength steel's superior mechanical properties enable offshore structures to
carry heavier loads and accommodate larger equipment, increasing their operational
capabilities and efficiency.
Enhanced Safety and Reliability
The use of high-strength steel in critical offshore components, such as risers, jackets,
and subsea equipment, enhances the safety and reliability of offshore installations,
reducing the risk of structural failure and accidents.

30
Design Flexibility
High-strength steel offers design flexibility due to its ability to support longer spans
and thinner profiles. This allows engineers to create innovative and efficient designs
for offshore structures.
Easy Weldability
High-strength steel is generally weldable, allowing for efficient fabrication and
assembly of offshore components. Proper welding procedures are essential to
maintain the material's mechanical properties and integrity.
Compliant with Industry Standards
High-strength steel used in offshore structures must meet stringent industry standards
and certifications, ensuring its performance, quality, and safety in challenging marine
environments.
Applications of High-Strength Steel in Offshore Structures:
Offshore Platform Jackets
High-strength steel is widely used in the construction of offshore platform jackets,
providing robust support for the topside facilities.
Subsea Pipelines
High-strength steel is employed in the fabrication of subsea pipelines to ensure the
integrity and reliability of the offshore transportation systems.
Offshore Mooring Systems
High-strength steel is utilized in the construction of mooring systems to secure
floating offshore platforms in position.
Risers and Tensioners
High-strength steel is used in risers and tensioners to support the vertical movement
and stability of floating platforms.
Offshore Wind Turbine Foundations
High-strength steel is used in the foundations of offshore wind turbines, providing the
required structural stability and load-bearing capacity.

31
5. Concrete with Advanced Additives
The majority of massive hydrotechnical structures require the usage of underwater
concrete technology (UWC), where major issue refers to avoiding washout of binding
agent from the concrete mixture. All underwater concrete techniques focus on
minimization of mixture’s contact with water during its supply for placement. Works
organisation and uninterrupted concrete placement is a key factor here. Usually,
concrete of class above C 20/25 are used. In case of underwater concreting, the
requirements on technological process are more important than the concrete strength
properties. In order to ensure a high liquidity of the mixture and to avoid binding
agent losses, above 375 kg/m3 of cement and additives per 1 m3 of concrete it is
assumed. Irrespectively of UWC method, special additives AWA (anti-washout
admixture) and admixtures - HRWR (high-range water-reducing admixture) shall be
used [81-83]. Application of new generation admixtures and additives, like AWA,
HRWR is more and more popular. Economic reasons related to proper organisation of
works [84] and variation-prone rheological and physical and mechanical properties of
concrete make us believe that the structures operated in water are most popular here.
In most cases, pebble or crushed-stone aggregate is used in underwater concrete.
Mixture placed under water should be resistant to segregation and water dilution, it
must spread out readily and be self-compacting [85-86]. Mineral additives used
mainly in UWC include silica fumes added in the quantity of up to 8% of cement
weight and fly ashes, their content approximates to 20% of cement weight. Significant
improvement to the underwater concrete technology was noted in previous years, to
open an opportunity for concrete as the material of the future. Many academic centres
carry out tests on mixtures of cement with the addition of fly ashes, calumite or
fluidized bed slag, zeolite, metakaolin and microsilica [87]. Advantageous influence
of additives on concrete properties has already been proved, therefore additives are
commonly used in concrete production. In the case of underwater structures it is
possible to use dispersed reinforcement in a form of steel and polymer fibres [8]. The
possibility to modify mechanical properties of concrete makes the structure more
resistant to abrasion, erosion and corrosion [89]. Additionally, surface protection by
impregnation of precast elements immersed in water makes it possible to build
structures in highly aggressive environment [90].
Sometimes, in order to avoid difficult process of casting, precast concrete elements
are produced. They include foundations of wind power plant or lightweight concrete
slabs as foundations of floating houses [91]. Another aspect is monitoring of concrete
elements, both, during the concrete placement and exploitation of the structure.
Advanced measurement techniques in combination with numerical simulations allow
prediction and monitoring of the changes of thermal and strength parameters as well
as condition of underwater concrete over time [92-94].
Technology of concrete placement in a structure is important, this is the key factor of
quality and durability of the object. Any errors during underwater concrete casting are
usually disastrous for the structure and their repair is very expensive. They are,
however, not all the factors to be taken into account. Also, concrete components used
and concreting technology are of significant importance for the water organisms. The
aim of the paper is to determine the effect of underwater concrete components on

32
water parameters (pH and electrolytic conductivity) and intensity of settlement by
living organisms.
5.1. Selected admixtures and additives
Concrete with advanced additives, also known as high-performance or special
concrete mixes, has emerged as a viable construction material for specific applications
in offshore structures. These additives enhance the properties of conventional
concrete, making it more suitable for the harsh marine environment and the unique
challenges faced in offshore engineering. Here are some key additives and their
benefits in offshore structure applications:
Silica Fume
Silica fume is a byproduct of silicon metal production and is often used as a
pozzolanic material in concrete. When added to concrete, it enhances its compressive
strength, durability, and resistance to chloride ion penetration. This makes it well-
suited for offshore structures that are exposed to seawater and corrosive environments.
Microsilica
Microsilica, also known as condensed silica fume, is another pozzolanic material that
offers similar benefits to silica fume. It reduces the porosity of concrete, improving its
resistance to chemical attack and reinforcing its overall strength.
Fly Ash
Fly ash is a byproduct of coal-fired power plants and is used as a supplementary
cementitious material in concrete. When included in the mix, it improves the
workability and durability of concrete, as well as reduces the heat of hydration,
making it suitable for large concrete pours in offshore applications.
Polymer Additives
Polymer additives, such as latex or acrylic resins, are used to modify the properties of
concrete. They improve the concrete's flexibility, toughness, and resistance to
cracking, providing better performance in offshore structures subjected to dynamic
loads and environmental stresses.
Corrosion Inhibitors
Corrosion inhibitors are chemical additives that help protect the steel reinforcement
within the concrete from corrosion. In offshore structures, where exposure to seawater
and aggressive chemicals is common, these inhibitors play a crucial role in extending
the service life of the concrete.

33
Superplasticizers
Superplasticizers, also known as high-range water reducers, are used to increase the
workability of concrete without sacrificing its strength. The improved workability
allows for better concrete placement and compaction, critical in the construction of
complex offshore components.
Shrinkage Reducing Admixtures
Shrinkage reducing admixtures help control the drying shrinkage of concrete,
reducing the risk of cracking. In offshore structures, where concrete is exposed to a
marine environment and varying temperature conditions, these admixtures help
maintain the integrity of the concrete.
Lightweight Aggregates
In certain offshore applications where reduced weight is crucial, lightweight
aggregates can be used to produce lightweight concrete. This allows for easier
transportation and installation of components while maintaining adequate structural
strength.
Applications of Advanced Additives in Offshore Structures:
Offshore Platform Foundations
Concrete with advanced additives can be used for the foundation of offshore
platforms, providing durable and corrosion-resistant support structures.
Subsea Concrete Structures
In subsea applications, concrete with special additives can be employed for
underwater structures such as pipeline coatings, protection mats, and gravity-based
foundations.
Floating Production Units
Concrete with advanced additives can be utilized in floating production units, such as
floating production storage and offloading (FPSO) vessels, for their durability and
resistance to seawater exposure.
Marine Repair and Rehabilitation
In offshore repair and maintenance projects, concrete with appropriate additives can
be used to restore and strengthen existing structures, extending their service life.
The use of concrete with advanced additives in offshore structures offers enhanced
performance, increased durability, and improved resistance to the harsh marine

34
environment. Careful consideration of the specific offshore conditions and
engineering requirements is essential to selecting the most appropriate concrete mix
and additives for each application.
6. Advanced Coatings
The ocean is the place with the worst corrosive environment.
The corrosion area of the offshore platform can be divided into:
A. marine atmosphere
B. splash area
C. tidal range
D. full immersion area
E. Sea mud area
The offshore coating system includes primers, intermediate coat/paint and topcoats,
and the underwater parts also include antifouling paints.
6.1. Types of Offshore Paint
Various types of Offshore paints are as follows:
1. Acrylic Polyurethane Finish
2. High Build Epoxy Zinc-rich Primer
3. Inorganic Zinc-Rich Primer
4. Fluorocarbon Finish
5. Moisture Curing Epoxy High-build Anticorrosive Paint
6. High Build Epoxy Glass Flake Anticorrosive Paint
Fig. 17- Acrylic Polyurethane Finish

35
Fig. 18- High Build Epoxy Zinc-rich Primer
Fig. 19- Inorganic Zinc-Rich Primer

36
Fig. 20- Fluorocarbon Finish
Fig. 21- Moisture Curing Epoxy High-build Anticorrosive Paint

37
Fig. 22- High Build Epoxy Glass Flake Anticorrosive Paint
6.2. Coating System
Primer
Primer is based on high anti-corrosion primer. Commonly used primers include epoxy
zinc-rich primer, inorganic zinc silicate primer, and epoxy anti-rust primer. Zinc rich
primer is an organic or inorganic coating containing a high proportion of zinc powder
as a filler. The zinc rich coatings use high-build epoxy coating with a volume solid
content of more than 70%, strong adhesion, and surface tolerance.
Intermediate paint and top coat
The function of the intermediate coat and topcoat is to provide a protective layer for
the primer, slow down and limit the penetration of water vapor, oxygen and
chemically active ions. Commonly used topcoats in the marine offshore platforms
include aliphatic polyurethane paint and polysiloxane coatings. Aliphatic
polyurethane coatings are often used in conjunction with zinc-rich primers and high
build epoxy intermediate coat. The polysiloxane coating is directly matched with the
zinc-rich primer coating. Epoxy polysiloxane coatings have stronger corrosion
resistance, and acrylic polysiloxane coatings are better in decoration property.

38
6.3. Working Process of Offshore Paint
Surface treatment
Preparing the metal surface before coating is an important requirement. Among the
factors that affect the effectiveness of coating performance, surface cleanliness may
be the most important. Any scale, dirt, grease and rust must be completely removed
before painting to ensure that the coating film is completely and firmly attached to the
substrate. If the adhesion is insufficient, the barrier protection will fail.
The cleaning techniques used include pickling or shot blasting. Pickling is used for
metals coated by a galvanizing process. (Pickling is discussed in the article Using
pickling and passivation chemical treatments to prevent corrosion.) For offshore
structures and ships, sandblasting is the prescribed cleaning method. For structural
metals such as steel and alloy steel, abrasive cleaning methods are also used for
surface treatment.
Choosing the right protective coating
For surfaces that remain fully submerged, it is best to use barrier coating systems and
cathodic protection. Compared with metal spraying, spray paint has always been
considered the first choice for corrosion protection. Here, paint is used in multiple
layers to enhance corrosion protection. (Learn about polyurea coatings in flexible
coatings used to protect marine structures.)
Paint consists of pigments, binders and solvents. The pigment that constitutes the core
of the coating consists of solid particles, which are kept well dispersed by solvents
and binders. Coatings can be specially formulated to ensure the basic properties
required for specific applications, such as water resistance and scratch resistance. In
order to minimize coating defects, apply multiple layers of paint on the substrate.
Before applying the first coat, apply a primer on the substrate to improve adhesion.
Marine environmental protection coating
Impressed current systems cannot protect surfaces and waterline areas exposed to the
atmosphere, because splashing water can cause severe corrosion. The surface of the
waterline should be coated with the thickest and best epoxy resin. Cathodic protection
can protect the underwater hull, which is the area most prone to corrosion
deterioration and fluid turbulence.
Advanced coatings find extensive applications in various components of offshore
structures, providing protection, durability, and improved performance in the
challenging marine environment. Some key applications of advanced coatings in
offshore structures include:

39
Platform Jackets and Legs
Advanced anti-corrosion coatings are applied to the steel jackets and legs of offshore
platforms to protect them from seawater, salt spray, and corrosive chemicals. These
coatings help extend the life of the platform's supporting structures and reduce
maintenance requirements.
Subsea Pipelines
Anti-corrosion coatings are used on subsea pipelines to prevent corrosion caused by
exposure to seawater and aggressive chemicals. Additionally, abrasion-resistant
coatings may be applied to protect pipelines from impacts and abrasion during
installation and operation.
Marine Vessels and FPSOs
Advanced coatings are applied to the hulls and structures of marine vessels and
floating production storage and offloading (FPSO) units to protect them from
corrosion, UV radiation, and marine fouling.
Subsea Equipment and Components
Various subsea equipment, such as risers, manifolds, and subsea valves, can be coated
with anti-corrosion and abrasion-resistant coatings to enhance their durability and
reliability in harsh subsea conditions.
Platform Decks and Walkways
Anti-slip coatings are commonly applied to offshore platform decks and walkways to
improve safety by reducing the risk of slips and falls, especially in wet or oily
conditions.
Helidecks and Helipads
Advanced coatings are used on helidecks and helipads to enhance their durability,
corrosion resistance, and ensure safe helicopter landing and takeoff operations.
Buoyancy Modules and Floatation Devices
Buoyancy modules and floatation devices are coated with protective coatings to resist
seawater penetration, maintain buoyancy, and protect against corrosion.
Splash Zone Protection
In areas of offshore structures that are exposed to tidal or splash zones, advanced
coatings with high corrosion resistance, such as thermal spray coatings, are used to
protect against the corrosive effects of seawater.

40
Subsea Protection Mats
Protection mats are used to cover subsea equipment and pipelines to provide
additional protection against mechanical damage and abrasion. These mats are coated
with advanced materials to ensure long-lasting performance in underwater conditions.
Mooring Systems
Anti-corrosion coatings are applied to mooring chains and anchor systems to protect
them from the corrosive effects of seawater and ensure reliable performance.
Underwater Infrastructure
Advanced coatings are used on underwater infrastructure, such as underwater cables,
to protect against corrosion and abrasion from marine environments.
Overall, the application of advanced coatings in offshore structures is essential for
maintaining the integrity, safety, and efficiency of these critical assets in the
challenging marine environment. Proper selection, application, and maintenance of
coatings are crucial to ensuring their long-term effectiveness and enhancing the
overall performance and reliability of offshore structures.
7. Conclusion
The application of advanced materials in offshore structures has revolutionized the
offshore engineering industry, offering numerous benefits and solutions to address the
challenges posed by the harsh marine environment. The use of these innovative
materials has enabled the development of more efficient, durable, and sustainable
offshore structures, leading to improved performance, safety, and cost-effectiveness.
Key conclusions from the application of advanced materials in offshore structures
include:
Enhanced Corrosion Resistance
Advanced materials, such as fiber-reinforced polymers (FRPs), titanium alloys, and
high-performance coatings, provide superior corrosion resistance, significantly
extending the service life of offshore components. This enhanced durability reduces
maintenance requirements and enhances the long-term reliability of offshore
structures.
Weight Reduction and Improved Load Capacity
Materials like titanium alloys, FRPs, and high-strength steels offer high strength-to-
weight ratios, enabling the construction of lightweight yet robust offshore components.
This weight reduction facilitates easier transportation, installation, and increased load-
carrying capacity, contributing to more efficient and economical offshore operations.
Resistance to Fatigue and Dynamic Loads
Advanced materials are designed to withstand cyclic loading, impact, and dynamic
stresses, making them suitable for offshore structures subjected to waves, currents,

41
and operational activities. Their ability to resist fatigue ensures the structural integrity
and reliability of critical components.
Design Flexibility and Customization
Advanced materials, particularly FRPs and composite materials, offer greater design
flexibility, allowing engineers to create complex shapes and customized
configurations. This versatility facilitates the optimization of offshore structures and
supports innovative design solutions.
Environmental Sustainability
The use of advanced materials can lead to improved environmental sustainability in
the offshore industry. Lightweight materials reduce energy consumption during
transportation and installation, while anti-corrosion coatings extend the service life of
structures, reducing the need for replacements and minimizing environmental impact.
Safety and Performance
Advanced materials, such as non-magnetic titanium alloys and anti-slip coatings,
enhance safety on offshore platforms and vessels, mitigating the risk of accidents and
improving overall performance in challenging marine conditions.
Cost-Effectiveness
While some advanced materials may have higher initial costs, their superior
performance, reduced maintenance requirements, and extended service life result in
long-term cost savings for offshore operators.
As the offshore industry continues to evolve, the application of advanced materials is
expected to grow, driven by the need for increased efficiency, safety, and
environmental sustainability. However, it's crucial to recognize that each material has
specific limitations and considerations, necessitating careful material selection,
engineering design, and quality control during fabrication and installation.
Overall, the integration of advanced materials in offshore structures marks a
significant step forward in the pursuit of more resilient and efficient offshore
operations, paving the way for continued innovation and advancements in the offshore
engineering field.

42
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