API 682 specifies how a complete cartridge sealing system for petroleum, natural gas and chemical pumps must be designed, tested and documented, while DIN EN 12756 fixes only the installation dimensions, designations and material codes of component seals for end-suction centrifugal pumps. A seal built to EN 12756 fits any pump cavity sized to the standard, whichever maker supplied it, but the standard sets nothing about how well it seals.
A seal qualified to API 682 has been tested against the standard’s leakage and wear limits and carries a defined set of features, at a higher price. The two are rarely alternatives for the same pump: which one applies usually follows from the pump and the service.
What Is API 682
API 682 is the American Petroleum Institute’s standard for sealing systems on centrifugal and rotary pumps in the petroleum, natural gas and chemical industries, covering pump shaft diameters from 20 mm to 110 mm. It sets requirements for the seal, its accessories, piping, instrumentation, testing and documentation.
The current edition of API 682 is the 4th edition, published in May 2014 and reaffirmed in March 2022. The 3rd edition was also issued as ISO 21049; the 4th was issued by API alone, so a spec that cites ISO 21049 refers to the older text.
API 682 classifies seals by category, type and arrangement. The category sets the pump the seal is intended for and its operating window:
| API 682 category | Intended pumps | Temperature range | Maximum pressure |
|---|---|---|---|
| Category 1 | Chemical-duty pumps with ASME B73.1 and B73.2 seal chambers | −40 °C to 260 °C | 20 bar |
| Category 2 | API 610 pumps | −40 °C to 400 °C | 40 bar |
| Category 3 | API 610 pumps | −40 °C to 400 °C | 40 bar |
In the 4th edition, Category 2 and Category 3 seals differ only in their testing, seal qualification and documentation requirements, which are the most rigorous for Category 3.
What Is DIN EN 12756
DIN EN 12756 is the German edition of the European standard EN 12756, which sets the principal dimensions for installing single and multiple mechanical seals with rotating spring units in the seal cavity of centrifugal pumps, together with the seal designations and material codes to use.
DIN EN 12756 replaced DIN 24960 in March 2001. The same European text is published as BS EN 12756, NF EN 12756 and ÖNORM EN 12756, and many buyers still call it “DIN” or “DIN 24960”.
EN 12756 treats the seal as a component, without the gland plate and shaft sleeve.
The Difference Between API 682 and DIN EN 12756
What Each Standard Covers
API 682 specifies how a sealing system must be designed, built, tested and documented; EN 12756 specifies only the dimensions a seal needs to fit the pump cavity, plus its designation and material codes.
API 682 seals are supplied as cartridge assemblies, complete with gland plate and shaft sleeve.
Qualification Testing
API 682 requires every seal design offered as compliant to pass a qualification test, while EN 12756 contains no test requirement of any kind.
The API 682 qualification test simulates a long steady-state run followed by a process upset, with pressure and temperature changes and a loss of flush. Under the acceptance criteria, a qualified seal may leak no more than 1,000 ppm by volume of vapour, measured by EPA Method 21, or 5.6 g/h of liquid per pair of seal faces, and its face wear at the end of testing must be less than 1% of the available wear.
Every assembled API 682 seal is also air tested before shipment: pressurized with air to 1.7 bar, it may lose no more than 0.14 bar in five minutes.
A seal outside the scope of API 682, by design or by operating window, is classed as an Engineered Seal and has no special qualification requirement. When a seal is offered “to API 682”, ask whether the design itself has been qualified. For an EN 12756 seal, ask the supplier for its own test data.
Pumps and Seal Chambers
EN 12756 seals fit the ISO 3069 seal cavity of end-suction centrifugal pumps built to EN 733 and EN 22858. API 682 is referenced normatively in API 610 and also applies to ASME B73.1, ASME B73.2 and API 676 pumps, new or retrofitted.
ISO 3069 is not intended for slurries or for fluids with high solids content, so its cavities, and the EN 12756 seals that fit them, are not the choice for those duties.
An API 682 seal is unlikely to fit an EN 12756 cavity. Before specifying an API 682 seal for an EN 733 pump, check the seal drawing against the measured cavity.
Cost
An API 682 seal costs more than an EN 12756 seal, because the standard adds parts, testing and paperwork that a component seal does not carry.
Even Category 1, the least expensive API 682 category, costs more than a seal maker’s standard design for chemical-duty pumps.
How to Choose the Right One
Specify API 682 for API 610 pumps and for hazardous, flammable or toxic services in petroleum, natural gas and chemical plants. Specify EN 12756 for general-duty end-suction pumps built to EN 733 or EN 22858, where the aim is a component seal that any maker can supply to the same dimensions.
In chemical plants with ASME B73 pumps, a practical split is a seal maker’s standard non-API seal for most services and an API 682 Category 1 seal for the severe or critical ones.
Neither standard’s scope refers to the other, so a seal does not become API 682 compliant because it fits an EN 12756 cavity.
An EN 12756 replacement can come from any maker, while an API 682 replacement is matched to the installed seal’s drawing, part number or a sample of the old seal.