Reference profile
- Designation
- API 682
- Title
- Pumps — Shaft Sealing Systems for Centrifugal and Rotary Pumps
- Issuing body
- American Petroleum Institute (API)
- Current edition
- 4th Edition (ISO 21049 Equivalent)
- Status
- Active; global benchmark standard for mechanical seals and piping support systems in process industries.
- Category
- Mechanical Seal & Piping System Standard
Overview
API Standard 682 (ISO 21049) specifies requirements and gives recommendations for sealing systems for centrifugal and rotary pumps used in the petroleum, natural gas, and chemical process industries.
It aims to ensure zero hazardous emissions and guarantees a minimum continuous operational life of 25,000 hours (approx. 3 years uninterrupted service) without seal replacement.
Scope & Applicability
Covers
- Seal Categories: Category 1 (Non-API 610 pumps, -40°C to 260°C, < 22 bar); Category 2 (API 610 pumps, -40°C to 400°C, < 42 bar); Category 3 (Rigorous & critical services, -40°C to 400°C, < 42 bar with mandatory FMEA documentation).
- Seal Types: Type A (O-ring pusher seal); Type B (Non-pusher elastomer metal bellows seal); Type C (Non-pusher high-temperature metal bellows seal with flexible graphite).
- Seal Arrangements: Arrangement 1 (Single seal); Arrangement 2 (Unpressurized dual seal / Tandem with buffer fluid); Arrangement 3 (Pressurized dual seal / Double with barrier fluid).
- Standardized Piping Flush Plans: Plans 01, 11, 12, 13, 14, 21, 23, 31, 32, 52, 53A, 53B, 53C, 54, 62, 65A/B, 72, 74, 75, 76.
- Mandatory Cartridge Construction: Pre-assembled cartridge design with centering clips for mistake-proof installation on pump shafts.
Does NOT cover (exclusions)
- Soft gland packing seals or sealless magnetic drive pumps.
- Pump mechanical casing and hydraulic impeller design—refer to API 610.
- In-service seal refurbishment and lapping procedures—refer to seal vendor guidelines.
Key Requirements
Seal Type Selection (Types A, B, C)
- Type A (Pusher Seal): Uses dynamic elastomeric O-rings for secondary sealing. Standard choice for moderate temperatures (< 177°C / 350°F) and clean hydrocarbon fluids.
- Type B (Elastomer Metal Bellows): Uses a metal bellows assembly with O-ring secondary seals. Eliminates dynamic O-ring hang-up; ideal for viscous or fouling fluids.
- Type C (High-Temp Metal Bellows): Features Inconel/AM350 metal bellows and flexible graphite secondary seals. Designed for high temperatures (177°C to 400°C / 350°F to 750°F) such as hot oil and vacuum column bottoms.
Seal Arrangement Selection (Arrangements 1, 2, 3)
- Arrangement 1 (Single Seal): One seal face pair per cartridge. Used for non-hazardous, non-flammable fluids where minor leakage to atmosphere is acceptable.
- Arrangement 2 (Dual Unpressurized / Tandem): Two seal face pairs with unpressurized buffer fluid between seals (buffer pressure < process pressure). Outer seal acts as safety backup and routes leaks to flare/drain.
- Arrangement 3 (Dual Pressurized / Double): Two seal face pairs with pressurized barrier fluid between seals (barrier pressure > process pressure by at least 1.4 bar / 20 psi). Guarantees zero process fluid leakage to atmosphere.
Piping Flush Plan Selection
- Plan 11: Discharge recirculation through an orifice to the seal faces. Most common flush plan for clean fluids.
- Plan 23: Recirculation from seal chamber through a pumping ring and external seal cooler back to seal chamber. Essential for high-temperature water (boiler feed water) to prevent flashing.
- Plan 53A / 53B / 53C: Pressurized barrier fluid circulation systems for Arrangement 3. Plan 53A uses a nitrogen-pressurized reservoir; Plan 53B uses a bladder accumulator; Plan 53C uses a differential pressure piston accumulator.
Cartridge Construction & Qualification Testing
- Cartridge Design: All API 682 seals must be pre-assembled cartridge units with stainless steel gland plates, heavy studs, and centering clips.
- Qualification Test: Every API 682 seal model must undergo a rigorous 100-hour factory qualification test on standardized test rigs simulating hydrocarbon fluids.
Technical Details
Barrier Fluid Pressure Differential: In Arrangement 3, barrier fluid pressure must be maintained at least 1.4 bar (20 psi) above maximum seal chamber pressure under all dynamic conditions.
Seal Face Materials Standard Combination: Reaction-bonded or Sintered Silicon Carbide (SiC) vs Premium Carbon Graphite is the standard recommendation for low friction and wear resistance.
Design Life Benchmark: Engineered to achieve a minimum 25,000 hours (3 years) continuous operation without leakage exceeding local environmental emission standards.
Engineering Notes
- Always specify Arrangement 3 (Pressurized Dual Seal) with Plan 53B or 54 for lethal, carcinogenic, or highly toxic fluids (e.g. H2S rich amines, benzene, hydrofluoric acid) to ensure zero emission to atmosphere.
- Plan 53B (Bladder Accumulator) is preferred over Plan 53A in offshore platforms and high-pressure duties to prevent nitrogen gas absorption into the barrier fluid at elevated pressures.
- Verify seal flush fluid thermal capacity and cooler sizing to maintain seal chamber temperatures below 80°C (176°F) for elastomer O-ring longevity.
Related Standards
- API 610
Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries (Defines seal chamber envelope).
- ISO 21049
Pumps—Shaft sealing systems for centrifugal and rotary pumps (International equivalent to API 682).
- API 614
Companion or referenced standard; verify its exact relationship in the adopted edition.
Source, Edition & Status
- Publisher
- API
- Edition Year
- 2014
- Industries
- Petrochemical, Refinery, Chemical, Oil & Gas
- Content Status
- published
- Last Reviewed
- 2026-07-01
- Last Updated
- 2026-07-01
- Verified By
- Engineering Reviewer
- Official Link
- www.api.org
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