API 610 BB2 and BB5 are between-bearing pump configurations for high-pressure refinery and chemical service. This guide compares BB2 (radial split, single/double stage) and BB5 (radial split, multistage) to help engineers select the right configuration.
API 610 BB Configuration Overview
Between-Bearing Design
- Shaft supported by bearings at both ends (overhung impeller eliminated)
- Advantages: handles high power, long shaft, stable, low deflection
- Use: high flow, high pressure, critical refinery/chemical service
- Types: BB1 (axially split), BB2 (radially split, single stage), BB3 (axially split, multistage), BB5 (radially split, multistage)
- Consider: pressure rating, temperature, maintenance access
API 610 BB Types
| Type | Split | Stages | Pressure | Use |
|---|---|---|---|---|
| BB1 | Axial | Single/double | Medium | General refinery |
| BB2 | Radial | Single/double | High | High pressure, high temp |
| BB3 | Axial | Multi | Medium-high | Boiler feed, water |
| BB5 | Radial | Multi | Very high | High pressure, severe |
BB2 (Radially Split, Single/Double Stage)
Design Features
- Radial split: casing halves joined perpendicular to shaft (bolt circle)
- Single or double suction impeller (double for high flow)
- Pressure rating: up to 4500 psi (310 bar) or higher
- Temperature: up to 800°F (425°C) or higher
- Advantages: high pressure capability, robust, good for severe service
BB2 Applications
- Refinery: charge pumps, reflux pumps, high-pressure hydrocarbon
- Chemical: high-pressure reactors, high-temp circulation
- Power: boiler feed (single stage, high pressure)
- Gas processing: amine, glycol, high-pressure injection
- Typical: flow 100-2000 m³/h, head 100-500m (single stage)
BB2 Advantages
- High pressure: radial split handles high pressure better than axial
- High temperature: radial split gasket better at high temp
- Robust: between-bearing, heavy casing
- Single stage: simpler than multistage, fewer parts
- Maintenance: casing removal (radial split, heavier than axial)
BB2 Limitations
- Single stage: limited head (need high speed or large impeller)
- Heavy casing: radial split is heavy, harder to maintain
- Cost: more expensive than OH2 for moderate conditions
- Footprint: larger than overhung pumps
- Consider: if head >500m, need BB5 (multistage)
BB5 (Radially Split, Multistage)
Design Features
- Radial split: multiple stages in series (segmental or barrel design)
- Stages: 2-12+ (each adds head)
- Pressure rating: up to 10,000 psi (690 bar) or higher
- Temperature: up to 800°F (425°C) or higher
- Advantages: very high pressure, multistage, robust, severe service
BB5 Applications
- Refinery: hydrocracker feed, high-pressure injection (100+ bar)
- Chemical: high-pressure reactors, urea, methanol synthesis
- Power: boiler feed (high pressure, >100 bar)
- Gas processing: high-pressure injection, CO2 sequestration
- Typical: flow 50-500 m³/h, head 500-3000m (multistage)
BB5 Advantages
- Very high pressure: multistage, radial split (barrel design)
- High temperature: radial split gasket, robust casing
- Efficiency: multiple small stages (each near BEP)
- Thrust balancing: balance drum or disc (multistage)
- Severe service: designed for extreme conditions
BB5 Limitations
- Complex: multiple stages, more parts, higher cost
- Maintenance: more complex (rotor removal, stage assembly)
- Cost: significantly more expensive than BB2
- Footprint: longer (multiple stages)
- Consider: if single stage sufficient, BB2 is simpler/cheaper
BB2 vs BB5 Comparison
| Parameter | BB2 | BB5 |
|---|---|---|
| Stages | 1-2 | 2-12+ |
| Max pressure | ~4500 psi | ~10,000+ psi |
| Max head | ~500m | ~3000m+ |
| Flow range | 100-2000 m³/h | 50-500 m³/h |
| Complexity | Moderate | High |
| Cost | Moderate | High |
| Maintenance | Moderate | Complex |
| Typical use | High pressure single stage | Very high pressure multistage |
Selection Guide
When to Choose BB2
- Head requirement: ≤500m (single stage sufficient)
- Pressure: ≤4500 psi (310 bar)
- Flow: high (100-2000 m³/h)
- Temperature: high (up to 425°C)
- Preference: simpler, lower cost, easier maintenance
When to Choose BB5
- Head requirement: >500m (need multistage)
- Pressure: >4500 psi (310 bar)
- Flow: moderate (50-500 m³/h)
- Temperature: high (up to 425°C)
- Severe service: hydrocracker, high-pressure injection, boiler feed
Consider BB3 (Alternative)
- Axially split multistage: easier maintenance than BB5
- Pressure: medium-high (≤200 bar typically)
- Temperature: moderate (≤300°C, axial split gasket limit)
- Use: boiler feed, water, moderate pressure hydrocarbon
- Consider: if pressure/temp moderate, BB3 easier to maintain
API 610-Specific Considerations
Hydrocracker Service
- Very high pressure: 100-200 bar (BB5 required)
- High temperature: 300-400°C
- Material: duplex, Hastelloy, Inconel (H2S, H2 environment)
- Seal: API 682 double seal, Plan 53B (barrier fluid)
- Consider: hydrogen embrittlement, high pressure sealing
Boiler Feed Service
- High pressure: 50-200 bar (BB3 or BB5)
- High temperature: 100-200°C (feedwater)
- Material: 12% Cr, duplex (high energy, cavitation resistance)
- NPSH: critical (hot water, high vapor pressure)
- Consider: first stage low-NPSH impeller, booster pump
High-Temp Circulation
- Moderate pressure, high temperature: BB2 (single stage)
- Temperature: 300-425°C (thermal oil, hot hydrocarbon)
- Material: 12% Cr, alloy steel (high temp strength)
- Thermal growth: centerline mounted, piping expansion
- Consider: thermal expansion, lubrication, seal flush cooling
Maintenance Comparison
BB2 Maintenance
- Casing removal: radial split (remove top half, heavy)
- Rotor: removable (between bearings, need coupling removal)
- Seal: accessible (cartridge seal, spacer coupling)
- Time: moderate (4-8 hours for overhaul)
- Consider: lifting equipment (heavy casing)
BB5 Maintenance
- Rotor removal: pull from end (segmental design) or remove barrel cover
- Stages: multiple impellers, diffusers, stage assemblies
- Balance: thrust balancing device (drum/disc) inspection
- Time: complex (8-24 hours for overhaul)
- Consider: specialized tools, trained technicians, spare rotor
Common Issues
- Wrong selection: BB2 for too high head (inefficient, unstable). Use BB5 for >500m.
- BB5 overkill: High cost, complexity for moderate conditions. Use BB2 if single stage sufficient.
- Thermal growth ignored: Nozzle loads, misalignment. Centerline mount, expansion loops, cold alignment offset.
- High pressure sealing: Seal failure, leakage. API 682 double seal, Plan 53B, proper flush.
- NPSH insufficient: Cavitation, damage. Low-NPSH first stage, booster, improve suction.
- Balance device wear: Thrust bearing failure. Inspect balance drum/disc, monitor thrust bearing temp.
- No spare rotor: Long downtime. Keep spare rotor (especially BB5).
- Improper alignment: Bearing/seal failure. Laser align, correct for thermal growth.
Procurement Recommendations
- Determine required head: ≤500m → BB2, >500m → BB5
- Consider BB3 (API 610 BB3) for moderate pressure, easy maintenance
- Specify material per fluid (12% Cr, duplex, Hastelloy, Inconel)
- For hydrocracker: specify BB5, duplex/Hastelloy, API 682 double seal
- For boiler feed: specify multistage, low-NPSH first stage, 12% Cr
- Require API 610 compliance (L10 bearing life, vibration, testing)
- Specify centerline mounting for high temp (thermal growth)
- Include spare rotor (especially for BB5, critical service)
- Require performance test, NPSH test, mechanical run test
- Verify supplier has BB2/BB5 design and application experience
Related Industries
API 610 BB2 vs BB5 selection applies to oil & gas (refinery hydrocracker, pipeline, upstream), petrochemical (ethylene, ammonia, methanol), chemical processing (high-pressure reactors), power generation (boiler feedwater), and gas processing (high-pressure injection). The core principle — selecting between single-stage BB2 and multistage BB5 based on head, pressure, and severity requirements — is consistent across all high-pressure critical pump applications.