Optimization in mechanical seal design for api 682 category i applications ijariie 2015

Vol-1 Issue-5 2015 IJARIIE-ISSN(O)-2395-4396
1505 www.ijariie.com 945
OPTIMIZATION IN MECHANICAL SEAL
DESIGN FOR API 682 CATEGORY 1
APPLICATIONS
Akshay S. Kunkolienkar1
, Vikas R.Deulgaokar2
1
Design Engineer, Mechanical Engineering, Savitribai Phule Pune University,
EagleBurgmann, Maharastra, India
2
Associate Professor, Mechanical Engineering, Savitribai Phule Pune University, Maharastra, India
ABSTRACT
The paper covers development of mechanical seal design to optimize the adaptive part for API 682 category 1
applications. Under the guidelines of Forschungskuratorium Maschinenbau (FKM) the static strength is
investigated using local stresses. Static structural load case is carried out on the adaptive parts with non-average
element-nodal stresses. The new design performance is investigated using finite element analysis in terms of
equivalent stress. Improved features in the design and their effects on manufacturing benefits, seal performance
leading final product cost/weight optimization are discussed. Evaluation of centrifugally cast stainless steel raw
material instead of forged wrought raw material is discussed.
Keyword : - Finite Element Analysis, Localized Stress, Static Utilization, Mechanical Seals.
1. INTRODUCTION
Mechanical seal is a commonly used device industry having application like pumps, compressor, agitators
and mixers to prevent the fluid/gas leakage into the surrounding. Mechanical seal is located between the stationary
housing and rotating shaft. [4] Centrifugal or positive displacement pumps used in industries having applications
involving hydrocarbon media follow API 682 and ISO 20149 technical standards for mechanical seals. [11-15]. Seal
faces are one of the basic mechanical seal components which get wearied and have to be regularly replaced. A
cartridge unit of mechanical seal means an assembly consisting of seal faces, secondary sealing element, springs,
shaft sleeve and adaptive parts. This complete unit can be directly assembled on the pumps. Adaptive parts in the
mechanical seal have a long life as manufactured with stainless steel material with properties like corrosion
resistance, aqueous usage, chemical resistivity, and elevated temperature environment. Adaptive parts are one of the
costliest parts in the mechanical seal cartridge unit. Earlier literature revels that the mechanical seal operation is
dependent on closing and opening force. [4] These forces depend on media pressure, spring forces and secondary
sealing element positions. The major design constrains for adapter parts of mechanical seal are the min & max
pressure, temperature condition, impeller speed and operating environment. Adaptive part design depends on load,
complexity in shape, manufacturing processes and material selection. There are different arrangements for
mechanical seal in the API 682, amongst which category 1 application with single seal arrangement 1 and dual seal
with face to back arrangement 3 is considered for the analysis. [11-15] The single and double seal arrangement is
shown in the Figs. 1 and 2 as below.
The adaptive parts for the single mechanical seal includes shaft sleeve and the cover, while for the dual seal
arrangement an additional part Adapter is included in between the cover and pump housing. The stationary element
for the single seal is the cover and rotating is the shaft sleeve, while for the dual seal the additional adapter is
stationary. Manufacturing of adaptive parts using centrifugal casted raw material is considered under this study. API

682 tells pressure containing parts made from cast material has to pass the liquid penetration test as per ASME VIII,
Division 1, and Appendix 7. [11-15]
Fig -1: Arrangement 1 type mechanical seal Fig -2: Arrangement 1 type mechanical seal
2. DESIGN CONSIDERATION FOR ADAPTIVE PARTS
The improvised adaptive components design consideration includes operating conditions, material
selection, and pressure distribution over the sealing elements and forces imposed. The present study considers
pressure value of 20 bar on the seal faces and Temperature range from 20°C to 176°C. The basic components of the
mechanical seal are depicted in the Fig. 3 as below. The material detail composition consideration of individual
components of mechanical seal is shown in the Table I.
Fig - 3: Mechanical Seal Basic components
Table - 1: Material composition for Seal Components
Components Material
Seal Faces Carbon graphite antimony impregnated, Silicon carbide, Sintered
Pressure-less
Stationary Seal Silicon carbide, Sintered Pressure-less
O-rings Fluorocarbon rubber, Per-fluoro-carbon rubber
Springs Nickel-Chromium-Molybdenum Alloy, Hastelloy C-4 & C-276
Adaptive Parts Chromium-Nickel-Molybdenum Steel (SS 316L / 1.4404) &
Chromium-Nickel-Molybdenum Cast Steel (1.4409)

Pressure distribution on the adaptive parts is the important parameter in addition to temperature and
material properties. Pressure distribution on the mechanical seal completely depends on the position and location of
the secondary sealing element based on the consideration that the seal is balanced. The hydro static forces due to the
fluid and spring force distributed on the new improvised adaptive part designs is shown in the Fig. 4. The worse
pressure condition of fluid is considered and the forces are calculated. The relative forces based on the pressure
combination are shown in the Table II.
Fig - 4: Pressure and Force Distribution Diagram
P1 : Pressure between the seals
P2 : Barrier Fluid Pressure between the seals
Fp : Force directed to the sleeve through the pin
Fs1Total : Total Spring Force imposed on seal faces
FT1 : Force acting on adapter due to sleeve (Media Pressure) and springs
FT2 : Force acting on cover due to sleeve (Barrier Fluid Pressure) and springs
Fs2 : Force due to the seal mounting screws acting on adapter though cover
Fs3 : Force due to the seal mounting screws
N : Rotation of impeller shaft
Table - 2: Calculated force distribution at worse operating condition
Components Sleeve Adapter Sleeve
N (rpm) 0 0 0
P1 (Mpa) 2.2 0 0
P2 (Mpa) 2.4 3.6 3.6
Fp (N) 827.5 - -
Fs1 Total (N) 202 202
FT1 (N) 0 0
FT2 (N) - 10495
Fs2 (N) 1746 -
Fs3 (N) 8810 8810

For the seal analysis boundary conditions are considered based on different combination of pressure at seal
P1 and intermediate pressure P2 at two different operating speeds as shown in Table III. These are the optimum
values to which mechanical seal would operate.
Table - 3: Operating condition/Boundary condition for seal analysis
Sr. No. N (rpm) P1 (Mpa) P2 (Mpa)
Seal Faces 0 2.2 0.05
Stationary Seal 0 2.2 2.4
O-rings 0 0 3.6
Springs 3600 2.2 0
Adaptive Parts 3600 2.2 2.4
With the aid of pressure loaded area, the force acting on the adaptive parts is evaluated. In the present
analysis the total spring force on the seal faces is calculated as 20N. The spring selected is compression type with
20.2N force over a length of 12.3 mm. The total of 10 such springs force along with the hydrostatic force creates a
closing force over the seal faces. Thus a new mechanical seal is devised based on the above specification and
respective parameters. Computer aided modeling is used to prepare the Adaptive part models. To avoid the
complexities the details of each component dimensions are not provided. A pictorial comparison of new and old
design is shown in Fig. 5. The new design features eliminates the critical manufacturing areas.
Fig - 5: Comparative pictures for new and old component designs

In the old design, for the turning operation a special Parting and Grooving Turning Tool had to be used in
order to machine some critical areas as depicted in the Fig. 6. In the new design this is eliminated by using different
type of seat and O-Ring grove. Thus the turning operation could be carried out with general turning tool. Horizontal
pin in old design is replaced with vertical one, eliminated complexities that occurred due to the usage of long drills
during manufacturing holes in the shaft sleeve.
a: Improved design b: Existing design
Fig - 6: Comparative pictures for new and old adapter design
3. STATIC STRENGTH ASSESSMENT
Analytically assessment of static strength is carried by evaluating the degree of utilization for equivalent stress.
Degree of utilization is based on analytical relations involving static component stress, equivalent stress and total
safety factor. The inter relationship between the parameter is given as in (1).
(1)
: Degree of utilization for equivalent stress
: Equivalent Stress
: Static component stress
: Total safety factor
Finite element analysis is used simulate adaptive parts. Dimensional details and geometrical criticalities of
adaptive parts are considered while preparing the CAD model. These solid models are imported into analysis
environment (ANSYS). To avoid possible errors these imported geometries are evaluated. Further solid tetrahedral
element method is used for model meshing. A typical structure of ANSYS used for evaluation of can be seen in Fig.
7 below.
Fig - 7: ANSYS Structure for component evaluation

Using nodes the above mentioned boundary conditions are applied. In the case of sleeve the degree of
freedom of inner circumference of the sleeve is arrested. The nodes at the guides provided for bolting on the cover
are constrained with zero displacements. Forces and pressure are imposed on respective area as shown in Fig. 4.
These areas are exposed to the same magnitude of pressure during practical condition. Static structural analysis is
carried out on the adaptive parts. Based on the analysis the deformation and equivalent stress for the worse operating
condition is identified. With the help of convergent command, mesh refinement is carried out to investigate the
maximum stress region. Using this command more accurate equivalent stress evaluation is investigated. Convergent
range is specified to be 2% in the present analysis. After the completion of convergence, the static stress assessment
is carried out to evaluate degree of utilization using local stresses under FKM guidelines. [5]
Engineers dealing with design and calculation in mechanical engineering and related fields of industry use
FKM assessment for analytical strength assessment. Static strength and fatigue strength is well described in the
guidelines. FKM Guidelines is valid for components made from steel, cast steel, or cast iron materials with
temperatures ranging from -40°C to 500 °C, as well as for components from aluminum alloys and cast aluminum
alloys. It allows an assessment considering nominal stresses, local elastic stresses derived from finite element or
boundary element analyses, from theoretical solutions using mechanics, or from any measurements. [5]
The FKM assessment is carried and stress plots for shaft sleeve, cover and adapter are given in Fig 8,9,10
respectively.
Fig - 8: Equivalent Stress plot for the sleeve
Fig - 9: Equivalent Stress plot for the adapter

Fig - 10: Equivalent Stress plot for the cover
3.1 FKM report of Finite Element Analysis
The FKM results of the equivalent stress for static utilization percentage are tabulated in Table II as below.
From the values of static stress we observe that for the cover and adapter the percentage of stress utilization is
improved as compared to the old design. For sleeve the stress values are increased, but they fall under acceptable
limits.
Table - 4: Percentage degree of Static Utilization for Adaptive Parts
Adaptive Parts
Static
Utilization
(New Design)
Static
Utilization
(Old Design)
Shaft Sleeve 97.50% 55.55%
Adapter 96.32% 223.91%
Cover 84.75% 141.23%
4. CONCLUSION
From the finite element analysis carried for shaft sleeve, adapter and cover following are the inferences drawn.
i. Stress utilization improvements for critical manufacturing area for all components were observed.
ii. Finite element analysis values of stress and deflection shows significant changes in stress patterns as
compared with the old design.
iii. Manufacturing method i.e. casting instead of conventional forging is employed, affects in reduction cost
of the final product.
iv. Close co-relation between the values of static stress utilization is observed at some locations for analytical
and finite element analysis methods.
v. Static stress utilization for the components made by two material viz. wrought stainless steel and cast
stainless steel shows better product with enhanced capability and reduced cost be developed by using
centrifugal cast raw material.
5. ACKNOWLEDGEMENT
The authors would like to thank EagleBurgmann Hadapsar, Pune for providing opportunity to work on the
design improvements of optimized mechanical seal for API 682 category 1 application. The author would also like
to thank Mr. Peter Droescher, Head of Engineering Department Mechanical Seals (Pumps & Special Rotating
Equipment, EagleBurgmann Germany), Mr. Rolf Johannes (Research & Development, EagleBurgmann Germany),
and Mr. Viktor Eichmann (EagleBurgmann Germany).

6. REFERENCES
[1] Mike Goodrich, A pump seal selection guideline complementing ISO 21049/ API 682, Sealing Technology,
Vol. 2010, Issue 7, July 2010, pp. 8–12.
[2] G. Chirita, D. Soares, F.S. Silva,„Advantages of the centrifugal casting technique for the production of
structuralcomponents with Al–Si alloys‟Mechanical Engineering Department, School of Engineering, Minho
University, Campus de Azure´m, 4800-058 Guimara˜es, Portugal, December 2006
[3] Thomas Böhm,Markus Fries,API revises API 682 standard for mechanical seals and supply systems, Sealing
Technology, September 2013, pp. 9–11.
[4] E. Mayor,Mechanical Seal(London – Boston : Butterworth Scientific, 1982 Reprint)
[5] Forschungskuratorium Maschinenbau (FKM), AnalyticalStrength Assessment of Components(6th edition,
2012).
[6] Johann Friedrich Guelich, Centrifugal Pumps, (New York: Springer-Verlag Berlin Heidelberg, 2008,2010)
[7] Malcolm Blair, Thomas L. Stevens, Steel Castings Handbook (6thEdition 1995, ASM International).Val S.
Lobanoff, Robert R.Ross, Centrifugal Pumps Design and Application (Second Edition, Gulf
ProfessionalPublishing, Houston, TX)
[8] A. Mateo , F. Heredero, G. Fargas , „Failure investigation of a centrifuge duplex stainless steel basket‟, (July
2011)
Adedipe Oyewole and Abolarin Matthew Sunday, „Design and fabrication of centrifugal casting
machine‟,IJEST, November2011
[9] Cokorda Prapti Mahandari and Ariyanto,Performance of centrifugal pump mechanical face seal,
GunadarmaUniversity, Jakarta-Indonesia
[10]Bob Flitney, „Mechanical seal housing design – are there real benefits, and do we want them?‟Sealing
Technology,. September 2004, pp. 10–14.
[11]American Petroleum Institute, Washington, D.C., API Standard 682,“Shaft Sealing Systems for Centrifugal and
Rotary Pumps,”(Fourth Edition, 2014)
Rotary Pumps,”(Fourth Edition, 2004)
Rotary Pumps,”(Second Edition, 2001)
Rotary Pumps,”(First Edition, 1994)
[15]Mandatory Appendix 7“Examination of Steel Casting Sealing Technology”ASME 8 Div. 1Handbook, pp. 413–
415.
[16]Malcolm Blair, Thomas L. Stevens, „Steel Castings Handbook” (6th Edition, ASM International).
[17]Vikas R. Deulgaonkar, Ashok G. Matani and Shrikant P. Kallurkar. 2015. Design Evaluation of Chassis
Mounted Platform for Off-Road Wheeled Heavy Vehicles, Int. J. Vehicle Structures & Systems, 7(3), 100-106.
[18]Vikas R. Deulgaonkar & Dr. A.G Matani, “Development and Validation of Chassis Mounted Platform design
for Heavy Vehicles”, International Journal of Vehicle Structures and Systems, 6(3), pp.51-57, 2014.
BIOGRAPHIES
Akshay S. Kunkolienkar a Design Engineer at EagleBurgmann India Pvt. Ltd. Pune.
He obtained his Bachelor‟s degree in Mechanical Engineering from Goa University,
India. He is perusing Master‟s in Engineering Design from Department of Mechanical
Engineering from Savitribai Phule Pune University, Pune, India.
Vikas R. Deulgaonkar Associate Professor at Department of Mechanical
Engineering, Marathwada Mitra Mandal's College of Engineering, Savitribai Phule
Pune University, Pune, India. He completed his PhD in Mechanical Engineering from
S.G B. Amravati University, Amravati. He has to his credit various research funds
from S.P Pune University and 14 Publications in International Journals of high repute
and impact factor more than 1.2.

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