Mechanical Seal Selection for API 610 Pumps: API 682 Guide

API 682 mechanical seals are the standard for API 610 pumps in refinery and chemical service, providing reliable sealing of hazardous and high-pressure fluids. This guide covers API 682 seal types, selection, flush plans, and maintenance.

API 682 Seal Fundamentals

API 682 Standard

• API 682: standard for shaft sealing systems for centrifugal pumps
• Categories: 1 (general), 2 (standard refinery), 3 (critical/severe)
• Types: A (single), B (double), C (dual tandem)
• Arrangements: 1 (single), 2 (double pressurized), 3 (dual unpressurized)
• Materials: seal faces, elastomers, metal parts per fluid

Seal Components

API 682 Seal Types

Arrangement 1 (single seal)

• Single set of seal faces (one rotating, one stationary)
• Arrangement 1: single, unpressurized
• Advantages: simple, low cost, easy maintenance
• Limitations: some leakage (controlled), not for hazardous
• Use: non-hazardous, water, light hydrocarbon, general service

Type B (Double Seal - Pressurized)

• Two sets of faces, barrier fluid between (pressurized)
• Arrangement 2: double, pressurized barrier fluid
• Advantages: zero process leakage, containment, failure warning
• Limitations: complex, expensive, barrier fluid system
• Use: hazardous, toxic, flammable, expensive fluid

Type C (Dual Tandem - Unpressurized)

• Two sets of faces, buffer fluid between (unpressurized)
• Arrangement 3: dual, unpressurized buffer fluid
• Advantages: containment if inner fails, lower pressure system
• Limitations: some leakage possible (to buffer), not zero
• Use: hazardous where full pressurized double not required

Cartridge Seal

• Pre-assembled seal (faces, spring, sleeve, gland) as unit
• Advantages: easy installation, correct setting, quick replacement
• Limitations: slightly more expensive than component seal
• Use: API 610 standard (cartridge required for most)
• Maintenance: replace complete cartridge (no field assembly)

Seal Face Materials

Silicon Carbide (SiC)

• Hard, chemical resistant, good thermal conductivity
• Advantages: excellent wear, chemical, thermal shock
• Limitations: brittle, expensive
• Use: chemical, abrasive, high temp (most common)
• Pair: SiC vs carbon (most common), SiC vs SiC (abrasive)

Carbon Graphite

• Self-lubricating, soft, good for dry running
• Advantages: self-lubricating, forgiving, low cost
• Limitations: wears faster, limited temp/chemical
• Use: general hydrocarbon, water, non-abrasive
• Pair: carbon vs SiC or tungsten (most common)

Tungsten Carbide

• Very hard, wear resistant, good for abrasive
• Advantages: excellent wear, impact resistance
• Limitations: heavy, limited chemical resistance, lower thermal shock
• Use: abrasive, slurry, catalyst, high pressure
• Pair: tungsten vs carbon or SiC

Elastomer Selection

EPDM

• Water, steam, ketones, alcohols, brake fluid
• Temp: -40 to +150°C
• Limitations: not for oil, hydrocarbon, fuel
• Use: water treatment, steam, chemical (non-oil)
• Cost: low

Viton (FKM)

• Hydrocarbon, oil, fuel, grease, mild acid
• Temp: -20 to +200°C
• Limitations: not for ketones, amines, hot water/steam
• Use: refinery, oil & gas, general hydrocarbon
• Cost: moderate

Kalrez (FFKM)

• Broad chemical resistance (near PTFE), high temp
• Temp: -20 to +300°C
• Advantages: excellent chemical, high temp
• Limitations: very expensive
• Use: severe chemical, mixed acid, high temp

PTFE / Spring-Energized

• Almost universal chemical resistance
• Temp: -200 to +250°C
• Advantages: excellent chemical, wide temp
• Limitations: creep, cold flow, requires spring energizing
• Use: severe chemical, pharmaceutical, high purity

API 682 Flush Plans

Plan 11 (Internal Recirculation)

• Fluid from discharge recirculates to seal chamber
• Components: orifice, internal passage
• Use: clean fluid, moderate temp (<80°C)
• Advantages: simple, no external supply
• Limitations: limited cooling, only clean fluid

Plan 23 (Recirculation with Cooler)

• Closed loop: seal chamber fluid circulated through cooler
• Components: pumping ring, cooler, orifice
• Use: hot hydrocarbon (>80°C), hazardous, valuable
• Advantages: efficient cooling, isolates process
• Limitations: more complex, pumping ring required

Plan 32 (External Flush)

• Clean external fluid injected into seal chamber
• Components: external supply, regulator, filter, orifice
• Use: dirty/abrasive, slurry, polymerization
• Advantages: clean flush, cools, keeps solids away
• Limitations: external supply, flush enters process

Plan 53B (Pressurized Barrier - Accumulator)

• For double seals: pressurized barrier fluid with accumulator
• Components: accumulator, reservoir, cooler
• Use: hazardous, toxic, flammable, expensive
• Advantages: zero leakage, pressure maintained, failure warning
• Limitations: complex, expensive

API 610-Specific Applications

Refinery Hydrocarbon

• Clean, cold: Type A single, Plan 11
• Clean, hot: Type A single, Plan 23 (cooler)
• Hazardous/flammable: Type B double, Plan 53B
• Faces: SiC vs carbon (standard), SiC vs SiC (abrasive)
• Elastomer: Viton (hydrocarbon), Kalrez (severe)

Chemical Processing

• Corrosive: Type A or B, faces SiC/SiC, elastomer per fluid
• Abrasive: Plan 32 (external flush), SiC/SiC or tungsten faces
• Hazardous/toxic: Type B double, Plan 53B
• Elastomer: EPDM (water/acid), Viton (solvent), Kalrez (severe)
• Consider: magnetic drive (no seal) for extreme hazard

High Temperature

• Plan 23: closed loop cooling (essential)
• Faces: SiC/SiC (thermal shock resistance)
• Elastomer: Kalrez, PTFE (high temp rated)
• Metal: 316SS, Hastelloy, Inconel (high temp strength)
• Consider: thermal expansion, metal bellows (no elastomer)

Abrasive/Slurry

• Plan 32: clean external flush (keep solids away)
• Faces: SiC/SiC or tungsten/tungsten (wear resistant)
• Sleeve: ceramic or Stellite (protect shaft from erosion)
• Gland: flushed, large ports (prevent clogging)
• Consider: dynamic seal or magnetic drive (extreme abrasive)

Seal Maintenance

Installation Best Practices

• Clean: seal faces, shaft, gland (no dirt, scratches)
• Lubricate: faces with clean process fluid or barrier fluid
• Set: cartridge seal correctly (follow manufacturer)
• Flush: verify Plan 11/23/32/53 connected, flow
• Start: prime pump, verify flush before startup

Monitoring

• Leakage: none (single), barrier fluid level (double)
• Temperature: seal gland temp (RTD or IR)
• Vibration: at seal area (early failure detection)
• Flush flow: sight glass or flow switch
• Barrier fluid (Plan 53): level, pressure (alarm on drop)

Common Failure Causes

• Dry running: #1 cause (no flush, no fluid)
• Wrong faces: incompatible with fluid (chemical attack)
• Flush failure: no flow, clogged orifice, cooler failure
• Misalignment: excessive face load, wear
• Contamination: solids in flush, abrasive wear

Procurement Recommendations

1. Specify API 682 seal per fluid conditions (Category 2/3 for API 610)
2. For hazardous: specify Type B double seal with Plan 53B
3. For hot fluid: specify Plan 23 with cooler, SiC/SiC faces
4. For abrasive: specify Plan 32 external flush, SiC/SiC or tungsten faces
5. Specify seal face materials per fluid (SiC, carbon, tungsten)
6. Specify elastomer per fluid (EPDM, Viton, Kalrez, PTFE)
7. Require seal flush plan drawing and P&ID
8. For critical pumps: specify seal leakage monitoring (barrier fluid level)
9. Include spare seal (cartridge) as critical spare
10. Require seal installation and maintenance manual
11. Verify supplier has API 682 seal application experience for API 610 pumps

Related Industries

API 682 mechanical seals apply to oil & gas (refinery, pipeline, upstream), petrochemical (ethylene, ammonia), chemical processing (acid/caustic/solvent), power generation (boiler feed, refinery), mining (slurry, abrasive), and pharmaceutical (high purity). The core principle — proper API 682 seal type, face material, elastomer, and flush plan selection based on fluid properties for reliable API 610 pump operation — is consistent across all critical pump applications.