API 682, Pumps, Shaft Sealing Systems.
API 682 is the American Petroleum Institute standard governing shaft sealing systems for centrifugal and rotary pumps in petroleum, petrochemical, and natural gas industries. The standard defines the seal-plan numbering convention used worldwide, Plan 11, Plan 13, Plan 23, Plan 32, Plan 52, Plan 53A, B, C, Plan 54, Plan 66, Plan 72-76, specifies seal-arrangement categories, 1, 2, 3 and types, A, B, C, and mandates the supplementary systems, flush, quench, barrier or buffer fluid that surround the seal itself. The current edition is API 682 4th edition, 2014. ISO 21049 is the international version.
What API 682, Pumps, Shaft Sealing Systems means.
Before API 682, mechanical seal selection was an engineering art that depended on the seal vendor's recommendation, the operator's historical reliability database, and project-specific risk tolerance. API 682 codified the relationship between the service, fluid properties, pressure, temperature, NPSH margin and the seal-plan number, so a project specification can call out 'API Plan 52' and every bidder understands the same flush, drain, vent, and reservoir arrangement. The seal-plan numbering convention is used worldwide and on pumps not formally bid to API 682. The standard also defines the testing required to qualify a seal arrangement for a service category, the seal-leakage acceptance criteria, and the documentation required per seal.
What is a seal plan number.
A seal plan number identifies the engineered supplementary system that surrounds a mechanical seal. Plan 11, the most common recirculates pumped fluid from the pump discharge through an orifice to the seal flush. Plan 13 recirculates from the seal chamber back to the suction. Plan 23 cools the seal flush through a pumping ring and external cooler. Plan 32 injects clean external fluid into the seal flush. Plan 52 supplies an unpressurized buffer fluid to a dual unpressurized seal. Plan 53A, B, C pressurizes a barrier fluid above process pressure for a dual pressurized seal. Higher-numbered plans, 66, 72-76 address specific containment, drain, and gas-buffer arrangements for hazardous services.
What does API 682 require beyond the seal plan.
API 682 specifies the seal arrangement, single seal, dual unpressurized, dual pressurized, gas-lubricated dry-running, the seal type, rotating flexible vs. Stationary flexible, balanced vs. Unbalanced, the face materials, silicon carbide, carbon, tungsten carbide, and the secondary-element material, PTFE, FKM, FFKM, perfluoroelastomer. Categorize-by-service is encoded as Category 1, 2, or 3, each tied to acceptance testing and design conservatism. The standard mandates the pressure rating of the seal-chamber housing, the gland-plate construction, the bolting torque, and the orientation of the seal-flush ports. Required documents include the seal cross-section drawing, the bill of materials, and the qualification test record.
What changed in the 4th edition.
The 4th edition, 2014 expanded the seal-plan menu to cover gas-buffered seals more comprehensively, added Plan 76, containment seal vent to disposal, and tightened the acceptance leakage criteria to align with newer regulatory expectations on volatile organic compound emissions. The qualification test sequence became more prescriptive. Hydrostatic test, static leakage test, dynamic test at rated and over-pressure conditions, cyclic test, and disassembly inspection. The categorization rules became more explicit about which services map to which category.
Common questions
Is API 682 mandatory if I specify API 610.
What is the difference between Plan 52 and Plan 53.
Can a non-API pump use API 682 seal plans.
What seal materials does API 682 mandate.
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