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 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. Documentation deliverables 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.
Frequently asked.
Is API 682 mandatory if I specify API 610?
API 610 12th edition references API 682 4th edition for the seal arrangement, so a pump specified to API 610 carries the API 682 seal-plan numbering by default. Projects that depart from API 682 must explicitly state the deviation in the project specification.
What is the difference between Plan 52 and Plan 53?
Plan 52 supplies an unpressurized buffer fluid to a dual seal where the buffer pressure is below the process pressure. Plan 53A/B/C pressurizes the barrier fluid above the process pressure, so any leakage flows outward (barrier into process) rather than inward (process into atmosphere). Plan 53 variants differ in how the barrier reservoir is pressurized (A: nitrogen blanket, B: bladder accumulator, C: piston pressurization).
Can a non-API pump use API 682 seal plans?
Yes. The seal-plan numbering convention is used universally on pumps bid to commercial standards (ANSI B73.1, ISO 5199) and on legacy pumps being retrofitted with new seals. Specifying a plan number gives the seal vendor and the pump shop a common reference; the API 682 documentation requirements may or may not apply.
What seal materials does API 682 mandate?
API 682 does not mandate specific materials but specifies that materials must be compatible with the process fluid, the temperature range, and the seal-flush arrangement. The standard requires a seal qualification test that demonstrates acceptable performance with the proposed materials and the proposed Plan. Vendors typically catalog face materials (silicon carbide vs. silicon carbide, carbon vs. silicon carbide, tungsten carbide combinations) and elastomer grades (FKM, FFKM, perfluoroelastomer) by service category.