API 682 is the American Petroleum Institute standard Pumps - Shaft Sealing Systems for Centrifugal and Rotary Pumps. The current edition is the 4th Edition (2014), reaffirmed in 2022; it was first published in 1994. It is the reference document for mechanical seals in refining, chemical and petrochemical service.
The single most useful thing to understand about it: API 682 is not a specification, and its Arrangements are defined by the standard as seals supplied per cartridge assembly. If you are specifying to API 682, you are specifying cartridge seals.
What API 682 is not
The European Sealing Association flags these as the points most often misread:
- API 682 is not a specification.
- Some end users have adopted API 682 into their own standards.
- API 682 does not attempt to cover all refinery duties.
- Default sealing recommendations in the standard do not imply technical preference but reflect installed base and experience.
What the standard is trying to achieve
API 682's objectives are that seals run continuously for 25,000 hours (3 years). Beyond that: Arrangement 2 outer seals should operate for at least 25,000 hrs at chamber pressure ≤ 0.7 bar. And: Seals should achieve compliance with local emissions regulations or a maximum of 1000 ppm.
These are performance objectives, not a performance specification. Seal performance is dependent on operation.
API 682 seal Categories 1, 2 and 3
The Category describes the seal chamber the seal is built for, and the operating window it is qualified against.
| Category | Seal chamber | Maximum pressure | Temperature range | Applies to |
|---|
| Category 1 | ASME B73.1 or ASME B73.2 | 20 barg (300 psig) | -40 °C to 260 °C (-40 °F to 500 °F) | Non-API 610 pump seal chambers |
| Category 2 | API 610 | 40 barg (600 psig) | -40 °C to 400 °C (-40 °F to 750 °F) | Seal chambers meeting API 610 chamber dimensions |
| Category 3 | API 610 | 40 barg (600 psig) | -40 °C to 400 °C (-40 °F to 750 °F) | As Category 2 but with increased documentation requirements |
- Seals covered by each Category are not required to be able to meet all maximum values listed.
- Any seal operating with service conditions outside the scope of the standard is designated an Engineered Seal (ES) and is not covered by the requirements of the standard.
A published figure you should check. Wikipedia's API Standard 682 article states 315 psi (22 bar) for Category 1 and 615 psi (42 bar) for Categories 2/3. Those figures do NOT match the European Sealing Association's summary of the 4th edition, which gives 20 barg (300 psig) and 40 barg (600 psig). MLC publishes the ESA figures and flags the conflict rather than silently picking one. Before you specify or buy against these limits, verify them in the current edition of the standard itself.
API 682 Arrangements 1, 2 and 3
Note the wording the standard itself uses - every Arrangement is expressed per cartridge assembly.
| Arrangement | In plain terms | As titled in the 4th edition |
|---|
| Arrangement 1 | a single seal | One Seal per Cartridge Assembly |
| Arrangement 2 | a dual unpressurised seal | Two Seals per Cartridge Assembly with a Liquid Buffer Fluid; and Two Seals per Cartridge Assembly with or Without a Gas Buffer Fluid |
| Arrangement 3 | a dual pressurised seal | Two Seals per Cartridge Assembly with a Liquid Barrier Fluid; and Two Seals per Cartridge Assembly with a Gas Barrier Fluid |
Seal Types A, B and C
API 682 defines three seal Types under Arrangement 1. MLC has not published the construction of each Type here because our sources confirm the Types exist without defining them, and we do not publish engineering detail we have not verified against the standard. This section will be completed from the standard itself.
The 31 API 682 piping plans (4th edition)
The 4th edition defines 31 standard seal piping plans. The 4th edition splits Plan 65 into 65A and 65B, and Plan 66 into 66A and 66B. This is the complete list as published:
Plan 01 Plan 02 Plan 03 Plan 11 Plan 12 Plan 13 Plan 14 Plan 21 Plan 22 Plan 23 Plan 31 Plan 32 Plan 41 Plan 51 Plan 52 Plan 53A Plan 53B Plan 53C Plan 54 Plan 55 Plan 61 Plan 62 Plan 65A Plan 65B Plan 66A Plan 66B Plan 71 Plan 72 Plan 74 Plan 75 Plan 76
MLC publishes the authoritative list rather than a paraphrase of what each plan does. If you need the schematic and the selection logic for a specific plan, that is in Annex G of the standard - or ask us below and a seal engineer will talk it through against your duty.
API 682 applies to spares and to upgrading existing plant
This is the line most people miss: “API 682 applies to seal spares as well as original equipment and may be applied for upgrading existing plant.”
You do not need a new pump to move to an API 682 seal. The standard explicitly covers seal spares and the upgrading of installed plant, which is how most sites actually get there - one pump at a time during planned maintenance, or as a standardisation programme across a duty class.
Related references
Sources
Every figure on this page is taken from the documents below. API 682 itself is a copyrighted standard and must be purchased from API; this page is a derived summary and a reading aid, not a reproduction.
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