API Standard 682

By the late 1980s, mechanical seals had been accepted as the preferred method for sealing rotating pumps for many years. However, mechanical seal standards were generally buried in other standards such as DIN 24960, ANSI B73 and API 610. All of these standards were primarily pump standards and any references to seals were directed at how mechanical seals would interact with pumps.[2]

API 610 is the API standard about centrifugal pumps and is primarily intended for use in the petroleum, natural gas and chemical industries. Although the 1st through 7th Editions of API 610 included specifications for mechanical seals, beginning with the 8th Edition, API 610 defers to API 682 for seal specifications.[2]

In the late 1980s a group of refinery equipment engineers and managers began to compare sealing solutions in refinery applications. This group, led by V. R. Dodd of Chevron, came up with a general plan and the American Petroleum Institute (API) agreed to establish a standard for mechanical seals: API 682. A Task Force was formed in 1990 and the first meeting was held in January 1991. This Task Force was composed of fourteen members from various refineries, seal and pump manufacturers. API 682, First Edition, was published in October 1994.[2]

One interesting aspect of API 682 is that it includes a strong set of defaults. That is, unless the user indicates otherwise, API 682 makes default choices for specifics such as:[2]

• Seal type
• Rotating or stationary
• Seal arrangement
• Seal configuration/orientation
• Materials
• Piping plan
• … many others.

Some statements within API 682 are normative, that is, required, whereas others are informative, that is, descriptive but not required. In particular, many of the illustrations are informative. This distinction has not always been apparent to the reader.[2]

Subsequent editions of API 682 have been published. The current edition is 4th Edition.

The first edition of API 682 was entirely new although parts of it were extracted from the pump standard API 610 and existing API standard paragraphs.

The mission statement for the 1st Edition was:

This standard is designed to default to the equipment types most commonly supplied that have a high probability of meeting the objective of at least three years of uninterrupted service while complying with emissions regulations.[3]

Although this mission statement no longer appears in the standard, it remains the basic principle driving the work of the API 682 Task Force and its relevance remains the same for the 4th Edition as it did for the 1st.

In addition to providing requirements for mechanical seals, the 1st Edition of API 682 also provided a guide on how to select the correct seal for a number of common refinery applications. In order to provide this seal selection guide, it was necessary to categorize applications into a number of services: [3]

• Non-hydrocarbon
• water
• sour water
• caustics/amines
• acids
• Non-flashing hydrocarbon
• Flashing hydrocarbon.

It was also necessary to categorize the many different type seals that were used in these services. Three seal types were designated: [3]

• Type A – O-ring pusher
• Type B – O-ring metal bellows
• Type C – flexible gasket (high temperature) metal bellows.

Prior to API 682, 1st Edition, multiple seals were designated as being either “tandem” or “double” seals; however, advances in seal design had rendered these classic terms obsolete. As a result, there was some confusion on how multiple seals were designated. The task force decided to use a more descriptive designation and chose to define dual seal arrangements. A dual seal would be two sets of sealing faces used in the same seal chamber. The fluid between these two sets of sealing faces could be either pressurized or unpressurized. Three standard arrangements were defined: [3]

• Arrangement 1 is a single seal
• Arrangement 2 is a dual unpressurized seal
• Arrangement 3 is a dual pressurized seal.

API 682 1st Edition did not include containment seals or dry gas barrier seals.

After having defined the services, seal types, and seal arrangements, a series of flowcharts were created to help in selecting a seal type, special materials or design requirements, and supporting piping plans.

API 682 seals were to have a high probability of three years of reliable service. In order to prove this, seal performance testing on process fluids under representative pressures and temperatures was required. These performance tests are called “Qualification Tests”. [3]

The general idea of the qualification test was to prove that the design was sound. The goal of the qualification test was to simulate a long-term steady state run followed by a process upset. The simulated process upset consisted of pressure changes, temperature changes and included loss of flush. The results of these tests were made available to the purchaser for evaluation. There was no acceptance criteria presented in API 682 1st Edition. [3]

In addition to the qualification test of the design, every API 682 seal, whether new or repaired, is to be pressure tested with air before being shipped to the end user. [3]

One of the major criticisms of API 682 1st Edition was that all the seals were “heavy duty” and therefore expensive with no alternatives for easy services. To some degree, this was intentional and was done in order to reduce inventory, promote familiarity with a limited number of seal types and to increase reliability. Another criticism of API 682 1st Edition was that it considered only API 610 pumps and only refinery applications. The chemical and petrochemical industries routinely use ASME pumps in addition to API 610 pumps. Broadening the scope of pumps covered by API 682 would allow standardized seals to be applied in a greater number of industries.[2] [4]

In 2nd Edition, the organization of API 682 was changed to conform to ISO standards: This reorganization means that there is no simple cross reference guide between 1st edition and 2nd edition paragraph numbers.[2]

For all practical purposes, API 682 3rd Edition is the same as 2nd Edition. The completed 2nd Edition was submitted to the ISO Organization for approval as their ISO 21049. At the time, API and ISO had an agreement to jointly issue standards. The ISO Organization made slight editorial changes to 2nd Edition, including correcting typographical errors and unit conversions. Therefore, API had to re-issue a corrected 2nd edition but choose to label it as 3rd edition. API 682 3rd Edition was published in September 2004.[5]

API and ISO no longer have the agreement to jointly issue standards. The 2004 issue of ISO 21049 is the only issue and plans to update it are unknown.[6]

A twenty-five member task force spent six years updating 3rd Edition to 4th Edition. [1] The 4th Edition of API 682 is organized similarly to the 2nd and 3rd Editions:[7]

1. Scope
2. Normative references
3. Terms, Definitions, and Symbols
4. Sealing Systems
5. General
6. Design Requirements
7. Specific Seal Configurations
8. Accessories
9. Instrumentation
10. Inspection, Testing, and Preparation for Shipment
11. Data Transfer

Annexes

• Annex A – Recommended Seal Selection Procedure
• Annex B – Typical Materials and Material Specifications
• Annex C – Mechanical Seals Datasheets
• Annex D – Seal Codes
• Annex E – Mechanical Seals Data Requirement Forms
• Annex F – Technical Tutorials and Illustrative Calculations
• Annex G – Standard Piping Plans and Auxiliary Hardware
• Annex H – Inspectors’ Checklist for All Seals
• Annex I – Seal Qualification Testing

API standards are reviewed every five years and re-issued every ten years. A new Taskforce for API 682 was formed in 2017 and preparations for 5th Edition are underway.