Cryogenic chemical pumps handle liquefied gases (ethylene, propylene, LNG, nitrogen, oxygen) at temperatures as low as -196°C. Material selection, NPSH, and sealing are critical. This guide covers pump selection for cryogenic ethylene, industrial gas, and LNG service.
Cryogenic Pump Services
| Service | Fluid | Temp | Key Characteristic | Pump Type |
|---|---|---|---|---|
| Ethylene transfer | Liquid ethylene (C2H4) | -104°C (bp) | Cryogenic, volatile (vapor pressure ~40 bar), flammable, precise, moderate flow | API 610 OH2 (316SS/LN2 steel, cryogenic, double seal, low-NPSH) or vertical cryogenic pump |
| Propylene transfer | Liquid propylene (C3H6) | -48°C (bp) | Cryogenic/cold, volatile, flammable, precise, moderate flow | API 610 OH2 (316SS, low-temp, double seal, low-NPSH) |
| LNG (liquefied natural gas) | LNG (methane + ethane) | -162°C | Very cryogenic, volatile, flammable, large flow, continuous, critical | Vertical cryogenic pump (submerged, 9% Ni/316SS, large flow) or API 610 OH2 (smaller flow) |
| LIN (liquid nitrogen) | LN2 (N2) | -196°C (bp) | Very cryogenic, inert, large flow, continuous, low cost | Vertical cryogenic pump (submerged, 316SS/9% Ni) or OH2 (smaller) |
| LOX (liquid oxygen) | LOX (O2) | -183°C (bp) | Very cryogenic, strong oxidizer (fire hazard), clean (no oil), precise, safety-critical | Vertical cryogenic pump (LOX-clean, 316SS, no lubrication contamination) or OH2 (LOX-clean) |
| LAr (liquid argon) | LAr (Ar) | -186°C (bp) | Very cryogenic, inert, large flow, continuous | Vertical cryogenic pump or OH2 |
| CO2 (liquid carbon dioxide) | LCO2 (CO2) | -20 to -50°C (pressurized) | Cold, high vapor pressure (~20 bar), inert, precise, moderate flow | API 610 OH2 (316SS, low-temp, double seal, high vapor pressure) |
| Ethylene fractionation reflux | Liquid ethylene (column reflux) | -100°C | Cryogenic, precise (reflux ratio), volatile, continuous, critical | API 610 OH2 (316SS, cryogenic, precise, double seal) |
| Cryogenic storage transfer | Various cryogens (from storage tank) | -100 to -196°C | Very cryogenic, intermittent, large flow, self-priming, low-NPSH | Vertical submerged cryogenic pump (no shaft seal, no leakage) or screw pump (smaller, self-priming) |
| Truck loading (cryogen) | LIN/LOX/LAr/ethylene (to tanker) | -100 to -196°C | Very cryogenic, intermittent, precise (metering), large flow, safety | Vertical cryogenic pump or OH2 (with flow meter) |
| Vaporizer feed | Cryogen (to ambient vaporizer) | -100 to -196°C | Very cryogenic, continuous, moderate pressure, precise | API 610 OH2 or vertical cryogenic pump |
| Seal gas / barrier fluid | Warm gas or clean fluid (for seal) | Ambient | Clean, precise, small flow, critical (seal protection) | Diaphragm metering (precise, clean) or small centrifugal |
Critical: Cryogenic Materials (-100 to -196°C) + Brittle Fracture
- Low-temp materials: Carbon steel = NOT below -29°C (brittle fracture). Use 316SS (austenitic, down to -196°C, standard for cryogens), 3.5% Ni steel (down to -100°C), 9% Ni steel (down to -196°C, LNG storage), aluminum alloy (down to -196°C, light duty). 316SS is most common for cryogenic pumps. Charpy V-notch impact testing required at service temp. Our low-temp API 610 range uses 316SS for cryogenic service.
- Thermal contraction: Pump shrinks at cryogenic temp — must account for thermal contraction. Centerline mounting. Flexible piping (expansion joints, cold box). Pre-cool pump slowly (avoid thermal shock). Warm-up before maintenance. Drain completely (liquid cryogen expands 600–800× when vaporizing — trapped liquid = overpressure/pressure rupture). Our cryogenic design includes thermal contraction compensation.
- Insulation: Cryogenic pumps must be insulated (cold box, vacuum jacket, perlite). Prevent frost/ice formation (moisture freezing). Vent gas (boil-off) safely. LOX = special (oxidizer, no combustible insulation). Our cryogenic systems include proper insulation.
Critical: NPSH + High Vapor Pressure
- Very low NPSH: Cryogens have high vapor pressure (ethylene ~40 bar at -100°C, LNG ~1 bar at -162°C, CO2 ~20 bar) — NPSH critical. Use low-NPSH impeller (large eye, inducer). Flooded suction (mount pump below tank — vertical submerged pump is ideal, no NPSH issue). NPSH margin ＞3m. Large suction piping (minimize losses). Avoid suction throttling. Vertical submerged pump = no shaft seal, no leakage, no NPSH problem (pump impeller submerged in liquid). Our vertical cryogenic pumps eliminate NPSH issues.
- Boil-off gas: Cryogens boil off — gas can enter pump (gas locking). Use vertical submerged (gas rises away from impeller). Low-NPSH design. Gas separation upstream. Pressure control. Our cryogenic design handles boil-off.
Critical: Sealing + Zero Leakage
- Sealing: Cryogenic fluids are volatile, flammable (ethylene, LNG, propylene), or oxidizing (LOX) — zero leakage required. Options: (1) Vertical submerged pump = no shaft seal (best for cryogens, no leakage). (2) Double mechanical seal with warm barrier fluid (plan 53B) — barrier fluid keeps seal warm (prevents ice formation, prevents brittle seal). (3) Magnetic drive pump (zero leakage, but check low-temp rating). Single seal = NOT acceptable for cryogens (leakage + ice formation). API 682 seal. Our zero-leakage cryogenic range prevents hazardous leaks.
- LOX special: Liquid oxygen is a strong oxidizer — any oil/grease = fire/explosion. Pump must be LOX-clean (degreased, no organic materials). Use compatible lubricants (dry film, no oil). No combustible materials near LOX pump. Grounded (static). Our LOX-clean pumps meet industrial gas standards.
Critical: Vertical Submerged vs Horizontal API 610
- Vertical submerged cryogenic pump: Impeller submerged in cryogen (in tank or sump). No shaft seal (zero leakage). No NPSH problem. Ideal for large flow, storage transfer, loading. Used for LNG, LIN, LOX, LAr. Longer shaft (critical speed, bearing design). Cold motor (submerged) or warm motor (long shaft). Our vertical cryogenic range is standard for industrial gas and LNG.
- Horizontal API 610 OH2: For smaller flow, process duty (reflux, vaporizer feed). Double mechanical seal with warm barrier. Low-NPSH impeller. 316SS. Easier maintenance (no tank entry). Our API 610 OH2 range handles smaller cryogenic process duties.
Material Compatibility
| Material | Ethylene (-104°C, flammable) | LNG (-162°C, flammable) | LOX (-183°C, oxidizer) | LIN (-196°C, inert) | CO2 (-40°C, high VP) |
|---|---|---|---|---|---|
| Carbon steel | NOT (＜-29°C brittle) | NOT | NOT | NOT | Fair (＞-29°C) |
| 3.5% Ni steel | Good (down to -100°C) | NOT (＜-100°C) | NOT | NOT | Excellent |
| 316SS | Excellent (down to -196°C) | Excellent | Excellent (LOX-clean) | Excellent | Excellent |
| 9% Ni steel | Good | Excellent (LNG standard) | Good | Good | Good |
| Aluminum alloy | Good (light duty) | Good | Good (LOX-clean) | Good | Good |
| PTFE/FFKM seals | Excellent (low temp) | Excellent | Excellent (LOX-compatible) | Excellent | Excellent |
| FKM (Viton) | Fair (low temp) | NOT (＜-20°C brittle) | NOT | NOT | Good |
| EPDM seals | NOT (hydrocarbon) | NOT | NOT (LOX) | Good | Good |
| Silicone | NOT (low temp + hydrocarbon) | NOT | NOT | NOT | NOT |
Critical: All cryogens = 316SS (or 9% Ni for LNG) + PTFE/FFKM seals + NO carbon steel below -29°C + NO FKM below -20°C. Ethylene/LNG/propylene = flammable + double seal/submerged + explosion-proof. LOX = LOX-clean + no oil + no combustibles. All = low-NPSH (flooded suction/vertical submerged) + insulation + thermal contraction + drain (prevent trapped liquid overpressure).
Common Problems and Solutions
Problem 1: Cryogenic pump cavitates (NPSH). High vapor pressure cryogen vaporizes. Solution: use vertical submerged pump (no NPSH issue) or low-NPSH API 610 OH2 (large eye, inducer). Flooded suction. NPSH margin ＞3m. Our vertical cryogenic range eliminates cavitation.
Problem 2: Pump shaft seal leaks (ice formation). Single seal leaks cryogen — ice forms — seal fails. Solution: use vertical submerged pump (no seal) or double mechanical seal with warm barrier fluid (plan 53B). Magnetic drive (zero leakage). Our zero-leakage range prevents cryogen leakage.
Problem 3: Brittle fracture (carbon steel). Carbon steel pump at -100°C — brittle fracture. Solution: use 316SS or 9% Ni API 610 OH2. Charpy impact test. Pre-cool slowly. Our low-temp range prevents brittle fracture.
Problem 4: LOX pump fire (oil contamination). Oil/grease in LOX pump — fire/explosion. Solution: use LOX-clean API 610 OH2 (degreased, no organic materials). No oil lubrication. Grounded. Our LOX-clean range meets safety standards.
Problem 5: Trapped liquid overpressure (maintenance). Cryogen trapped in pump — vaporizes (600–800× expansion) — pressure rupture. Solution: drain pump completely before maintenance. Vent valve. Pressure relief. Slow warm-up. Our cryogenic design includes drain/vent.
Selection Summary
- Ethylene: API 610 OH2 (316SS, -104°C, double seal, low-NPSH, flammable) or vertical submerged
- Propylene: API 610 OH2 (316SS, -48°C, double seal, low-NPSH)
- LNG: Vertical cryogenic pump (9% Ni/316SS, -162°C, submerged, large flow, flammable) or OH2 (smaller)
- LIN/LOX/LAr: Vertical cryogenic pump (316SS, -183 to -196°C, submerged, LOX-clean for O2) or OH2
- CO2: API 610 OH2 (316SS, -40°C, double seal, high vapor pressure ~20 bar)
- Reflux: API 610 OH2 (316SS, cryogenic, precise, double seal)
- Storage/loading: Vertical submerged cryogenic pump (no seal, no NPSH, large flow, intermittent) or screw pump (small, self-priming)
- Vaporizer feed: API 610 OH2 or vertical cryogenic (continuous, moderate pressure)
- Seal gas/barrier: Diaphragm metering (precise, clean, small flow)
- Critical: cryogenic = 316SS/9% Ni (NO carbon steel ＜-29°C) + PTFE/FFKM (NO FKM ＜-20°C) + vertical submerged (no seal + no NPSH) or double seal with warm barrier + low-NPSH + insulation + thermal contraction + drain (trapped liquid = rupture), LOX = LOX-clean + no oil + no combustibles, flammable = explosion-proof + zero leakage, all = API 610 for process + Charpy impact test + pre-cool
- Our API 610 OH2 covers horizontal cryogenic process; magnetic drive covers zero-leakage; metering covers seal gas. For cryogenic pump selection, talk to our chemical engineers with your cryogen, temperature, flow, and application.