API-682, 4th Ed - Centrifugal Pump Mechanical Seals. Overview and Selection Criteria

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API 682 is the most important specification for mechanical seals in petrochemical, chemical, and pipeline services globally. It has merged the components of seal design, testing, standards, and applications to give consumers and OEMs with a single source of information on mechanical seals. As seal technology has improved, the standard has grown to include new seal designs, materials, seal selection guidelines, and pipe layouts. The fourth edition, released in May 2014, is now available for purchase. This lesson will go over the significant changes included in the Fourth Edition and making easier the life of those in Design Engineering work to select the most convenient Seal based on fluid, configuration, service, safety conditions.

All shaft sealing proposed under this standard shall be capable of operating 25,000 hours without need of replacement due to wear and tear and a maximum screening value of 1,000 mlfm3 (1 ,000 ppm vol), measured by EPA Method 21, whichever more stringent (emission regulations).

The 4th Edition also includes the revised product coding system (Annex D). The proven classifi cation parameters „Category,“ „Arrangement,“ and „Type“ will be continued. They are the fi rst thing listed in the revised code - and provide information about the set-up and fi eld of use of the respective API seal. The arrangement includes seal arrangement: single seals (Arrangement 1) are differentiated as well as double seals with and without pressurization (Arrangement 2 and 3).

Other improvement, but not limited to in this standards, to guarantee the 25,000 hours of operation without need of replacement as above mentioned:

1. Adaptation of Pressure Limits: 20 Barg (Cat#1), 40 Barg (Cat#2/3).
2. Definition of vapor pressure margin.
3. Table of internal gap dimensions.
4. Optional bellow materila of Alloy 718, Seal Type B.
5. Addtional requirements of torque transmission.
6. Reduced minimum gap at the internal pumping device.
7. New API Plans 03, 55, 65A, 65B, 66 A, 66B, 99.
8. Hydrostatic level detection for Plans 52, 53A.
9. Temperature measurement of gas bubble for Plan 53B.
10. Minimum pipe wall thicknesses of 2.5 mm for welded joints.
11. etc.

The reader shall always keep in mind that this article shal be read with together the following standards:

• API-610 - Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries.
• API-614 - Lubrication, Shaft-sealing and Control-oil Systems and Auxiliaries for Petroleum,Chemical, and Gas Industry Services.
• ASME B73.1 - Specification for Horizontal End Suction Centrifugal Pumps for Chemical Process
• ASME B73.2 - Specification for Vertical In-line Centrifugal Pumps for Chemical Process
• SO 21049 - is the international standard for "Pumps — Shaft Sealing Systems for Centrifugal and Rotary Pumps", which is functionally equivalent to API 682. This standard provides specifications and best practices for the design, testing, and selection of mechanical seals and seal support systems in industrial pump applications.

MECHANICAL SEAL DEFINITION

A mechanical seal in a centrifugal pump is a key component that prevents fluid leakage along the shaft, keeping the fluid from escaping into the environment and pollutants out of the pump. The mechanical seal does this by forming a tight seal between the spinning shaft and the stationary pump housing, often employing faces, springs, and elastomers. These seals are often found where the pump shaft goes through the pump casing.

***JAES Company Youtube Video: https://www.youtube.com/watch?v=kl6mk-gzRb4

Main Function of Mechanical Seal in Centrifugal Pumps

• Leak Prevention.
• Reducing Wear and Tear.
• Environmental Protection.
• EnergyEfficiency.
• Extend Service Life.
• Lubrication.
• Safety.

SEAL CODE DESCRIPTION (API-682, Annex D)

In the following sections, we are going to describe every single one of the parts comprishing a Mechanical Seal Plan as well as the differnt kind of plan, allowing anyone to select the corresponding API Mechanical Seal more convenient for each application.

SEAL CATEGORY (API-682) (Cat#1/2/3)

• Category 1 (ASME B73.1/73.2) - Seals are intended for use in non-API 610 pump seal chambers, meeting the dimensional of ASME B73.1, B73.2 Seal Chamber dimension and their applications is limited to -40 C (-40 F) to 260 Celsius (500 F). and gauge pressure up to 2 Mpa (20 barg).
• Category 2 (API-610) - Seals are intended for use in API-610 seal chambers. Their application is limited to seal chamger temperatures from -40C (-40 F) to 400 C (750 F) and gauge pressure of 4 MPag (40 Barg).
• Category 3 (API-610) - provides the most rigorously tested and documented seal design. They meet the seal chamber envelope requirements of API 610 (or equal). . Their application is limited to seal chamger temperatures from -40C (-40 F) to 400 C (750 F) and gauge pressure of 4 MPag (40 Barg).

SEAL TYPES (API-682) -Type A/B/C

• Type A- Elastomeric - seal is a balanced, internally-mounted, cartridge design, pusher seal with multiple springs. Secondary sealing elements are elastomeric 0-rings. Temp up to 176C (350 F).
• Type B - Metal Below- seal is a balanced, internally-mounted, cartridge design (metal bellows) seal. Secondary sealing elements are elastomeric 0-rings. Temp up to 176C (350 F).
• Type C - Metal Bellow + Graphite, Higher Temp - seal is a balanced, internally-mounted, cartridge design (metal bellows) seal. Secondary sealing elements are flexible graphite. Temp up to 400 C (750 F).

Notes:

a) Type A and Type B seals are suitable for temperatures up to 176 oc (350 °F).

b) Type C seals are for high temperatures up to 400 oc (750 °F).

****Other types of seals could acceptable, but they shall be engineering designed and referred to as ES - Engineering Seal (or P.Eng)***.

SEAL ARRANGEMENT ( #1, #2 & #3)

• Arrangement 1 - (One Seal per Cartridge). Seal configurations having one seal per cartridge assembly.
• Arrangement 2- (Two Seal per Cartridge).Seal configuration having two seals per cartridge assembly, with the space between the seals at a pressure less than the seal chamber pressure. Options:
• face-to-back. Section 3.1.31. Dual seal in which one mating ring is mounted between the two flexible elements and one flexible element is mounted between the two mating rings and the pump process fluid is on the OD of the inner seal and barrier or buffer fluid is on the ID of the inner seal and OD of the outer seal.
• back-to-back. Section 3.1.7. Dual seal in which both of the flexible elements are mounted between the mating rings, the sealed fluid is on the ID of the inner seal, and the barrier or buffer fluid is on the OD of the inner and outer seal.
• face-to-face. Section 3.1.32. - Dual seal in which both of the mating rings are mounted between the flexible elements

• Arrangement 3 - (External supplied barrier fluid). Seal configurations having two seals per cartridge assembly, utilizing an externally supplied barrier fluid at a pressure greater than the seal chamber pressure.

Pnemothecnical Rule to Understand the API-682 Mechanical Seal Identification:

<ABB-CC>

• A - Mechanical Seal Arrangement (#1/#2/#3) - Define the seal robustness and compliance level.
• BB - Seal Type (CW, NC or CS) - Define the nature of contact between sealing surfaces.
• CC - Seal Arrangement ((FX, FL, CW, CS, FB, BB, FF, etc.) - Define the the Seal Positioning and Bushing Type.

Alternative Technology Designs and Sealing Methods (to Seal Arrangements)

1. Contacting Wet (CW) Seals. Seal design where the seal faces are not designed to intentionally create aerodynamic or hydrodynamic forces to sustain a specific separation gap (refer to 3.1.18).
2. Noncontacting (NC) Seal. Seal design where the seal faces are designed to intentionally create aerodynamic or hydrodynamic separating forces to sustain a specific separation gap (refer to 3.1.56).
3. Containment Seals (CS). with or without contacting. Seal design with one flexible element, seal ring and mating ring mounted in the containment seal chamber (refer to 3.1.20).

***API 682 PLAN as per API-682- Annex G***

Standard Piping Plans and Auxiliary Hardware

Herein, it is only included the most typical ones used in industrial service. For additional informatin, please refer to API-682, Annex G.

API PLAN 01:

API PLAN 02:

API PLAN 03:

API PLAN 55:

API PLAN 65A/65B:

***REFERENCES***

• "Mechanical Seals for Pumps," by W. Scott St. Clair, Hydraulics and Pneumatics. This text details the function and importance of mechanical seals in centrifugal pumps and the different types of seals used in various industries.
• API 682 – Pumps – Shaft Sealing Systems for Centrifugal and Rotary Pumps, 4th Ed – This standard provides technical definitions, specifications, and recommendations on mechanical seals used in industrial centrifugal pumps designed under API-610 and/or ASME B73.1 & 2.
• Overview of API-682 and ISO 20149 by Seal Solutions. Michael B. Huebner, Flowserve Corporation.
• Copyright © 2015 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station