Heat transfer fluid (thermal oil, hot oil) systems circulate high-temperature fluid for process heating in chemical, food, textile, and asphalt industries. Pumps handle hot oil (200–400°C), high vapor pressure, and thermal expansion. This guide covers pump selection for thermal oil and heat transfer fluid systems.
Thermal Oil Pump Services
| Service | Fluid | Temp | Key Characteristic | Pump Type |
|---|---|---|---|---|
| Thermal oil circulation (main loop) | Mineral oil or synthetic HTF | 200–350°C (mineral), 300–400°C (synthetic) | Very hot, high vapor pressure (synthetic), large flow, continuous, critical (process heating), low-NPSH | API 610 OH2 (centerline mounting, high-temp seal, alloy/carbon steel, low-NPSH) — standard for HTF |
| Boiler/heater feed | Cold return thermal oil (to heater) | 100–200°C (return) | Hot, large flow, continuous, critical, moderate head | API 610 OH2 or BB2 (carbon steel/alloy, high temp, large flow) |
| High-temperature synthetic (＞350°C) | Synthetic HTF (diphenyl/diphenyl oxide, e.g., Dowtherm A) | 350–400°C | Extremely hot, very high vapor pressure (~10 bar at 380°C), toxic (some synthetics), critical, low-NPSH, alloy | API 610 OH2 (Cr-Mo alloy, centerline, high-temp seal, double mechanical seal, low-NPSH) — special HTF pump |
| Thermal oil storage transfer | Cold/warm thermal oil | Ambient–100°C | Viscous (cold oil ~100 cP), large flow, intermittent, self-priming | Internal gear pump or screw pump (viscous, self-priming, positive displacement) or centrifugal (warm oil) |
| Thermal oil filtration | Thermal oil (with coke/carbon fines) | 150–250°C | Hot, abrasive (coke fines from oil degradation), moderate flow, continuous, bypass loop | API 610 OH2 (hardened seal faces, large passage, high temp) or gear pump (positive displacement) |
| Expansion tank circulation | Thermal oil (expansion tank) | 50–150°C | Warm, small flow, continuous, degassing, low-NPSH | Gear pump or small OH2 (warm oil, small flow) |
| Asphalt/bitumen heating (thermal oil jacket) | Thermal oil (to asphalt tank jackets) | 200–300°C | Hot, large flow, continuous, critical (asphalt must stay molten) | API 610 OH2 (carbon steel, high temp, large flow, centerline) |
| Reactor jacket heating | Thermal oil (to reactor jackets) | 200–350°C | Hot, precise (temp control), large flow, continuous, critical (reaction temp) | API 610 OH2 (high temp, precise flow with VFD, centerline) |
| Hot oil to heat exchanger | Thermal oil (to process exchangers) | 200–350°C | Hot, large flow, continuous, multiple users, critical | API 610 OH2 or BB2 (high temp, large flow, high efficiency) |
| Cooling (return line) | Cooled thermal oil (return to heater) | 100–200°C | Warm/hot, large flow, continuous, lower vapor pressure | API 610 OH2 (carbon steel, warm/hot, large flow) |
| Emergency/standby pump | Thermal oil (redundant) | 200–350°C | Hot, critical (no heat = process shutdown), auto-start, same as main | Same as main pump (100% standby, auto-start on pressure drop) |
| Thermal oil filling/draining | Cold thermal oil | Ambient–60°C | Viscous (cold), intermittent, small/moderate flow, self-priming | Gear pump or screw pump (viscous, self-priming, positive displacement) |
| Waste oil (degraded thermal oil) | Used thermal oil (with coke, degradation products) | Ambient–100°C | Abrasive (coke), viscous, corrosive (some), small flow, environmental | Gear pump or 316SS centrifugal (abrasion-resistant, corrosion) |
Critical: High Temperature (200–400°C) + Centerline Mounting
Thermal oil systems operate at extreme temperatures — thermal management is critical:
- Centerline mounting: At ＞200°C, pump casing expands significantly — centerline-mounted pump (API 610 OH2 centerline design) maintains shaft alignment as casing expands vertically. Foot-mounted pumps = misalignment at high temp = seal/bearing failure. API 610 OH2 centerline is standard for ＞200°C. Our centerline API 610 range handles thermal oil.
- High-temp mechanical seal: Standard seals fail at ＞200°C. Use high-temp mechanical seal with: plan 32 flush (cool, clean thermal oil injected into seal chamber — lowers seal temp), plan 53B barrier fluid (pressurized barrier), plan 62 quench (steam or air quench outside seal). Jacketed seal chamber (cooling water or cool oil). PTFE/FFKM or graphite seal faces (NOT FKM above 200°C). Silicon carbide vs silicon carbide or tungsten carbide faces. API 682 seal. Our high-temp seal arrangement handles thermal oil.
- Thermal expansion: Thermal oil expands ~10% from ambient to 300°C. Expansion tank (required). Piping expansion loops/bellows. Pump centerline mounting. Drain (hot oil expands — trapped = overpressure). Pressure relief. Our systems include thermal expansion compensation.
Critical: High Vapor Pressure (Synthetic HTF) + NPSH
- Synthetic HTF vapor pressure: Synthetic fluids (diphenyl/diphenyl oxide, e.g., Dowtherm A, Therminol VP-1) have very high vapor pressure: ~1 bar at 250°C, ~5 bar at 350°C, ~10 bar at 380°C. Mineral oil has lower vapor pressure (＜1 bar at 300°C). High VP = NPSH critical. Use low-NPSH impeller (large eye, inducer). Flooded suction (mount pump below expansion tank/heater). NPSH margin ＞3m (synthetic) or ＞1.5m (mineral). Pressurized expansion tank (increases NPSHa). Avoid suction throttling. Our low-NPSH API 610 range handles synthetic HTF.
- Cavitation damage: Hot oil cavitation = rapid seal/impeller damage (hot oil + vapor bubbles = erosion). NPSH margin critical. Suction piping large (minimize losses). Strainer with low pressure drop. Monitor suction pressure. Our low-NPSH design prevents cavitation.
Critical: Thermal Oil Degradation + Coke Formation
- Oil degradation: Thermal oil degrades at high temp (especially ＞max rated temp) and with oxygen (oxidation). Degradation produces: coke/carbon fines (abrasive), lighter fractions (high vapor pressure), acidic products (corrosion). Use oil rated for system temp (don't exceed max film temp — 20–30°C above bulk temp at heater wall). Inert gas blanket (nitrogen) in expansion tank (prevent oxidation). Filtration (remove coke fines). Oil analysis (periodic — viscosity, flash point, TAN, insolubles). Our filtration-ready pumps handle degraded oil.
- Coke fines abrasion: Coke from degraded oil is abrasive. Use tungsten carbide or silicon carbide seal faces. Hardened shaft/sleeve. Large passage. Bypass filtration (10–50 micron). Monitor oil condition. Our abrasive-resistant range handles coke fines.
Critical: Safety (Fire + Toxic + Burn Hazard)
- Fire hazard: Thermal oil at 300°C is above flash point of many mineral oils (autoignition ~350–400°C). Leak = fire. Zero leakage (double mechanical seal or magnetic drive). Fire detection. Emergency shutdown (ESD). Secondary containment. Cool-to-touch piping insulation. Fire extinguishers (Class B). Our zero-leakage range reduces fire risk.
- Toxic (synthetic): Some synthetic HTFs (diphenyl) are toxic — avoid skin contact, inhalation. PPE (gloves, respirator if mist). Secondary containment. Spill kit. Material safety data. Our sealed systems prevent exposure.
- Burn hazard: 300°C oil = severe burns. Insulation (personnel protection). Hot surface labels. Lockout/tagout (cool before maintenance). Drain/cool pump before service. Safety first.
Critical: Standby / Redundancy (Critical Service)
- 100% standby: Thermal oil pump failure = process shutdown (loss of heat = production loss, possible product damage). Use 100% standby pump (auto-start on pressure drop or main pump failure). Both pumps piped in parallel. Warm standby (standby pump kept warm with bypass flow — prevents thermal shock on startup). Regular exercise (run standby weekly). Our redundant systems ensure continuous heating.
Material Compatibility
| Material | Mineral oil (300°C, non-corrosive) | Synthetic (380°C, high VP, toxic) | Degraded oil (250°C, coke + acid) | Cold oil (ambient, viscous) |
|---|---|---|---|---|
| Carbon steel (WCB) | Excellent (standard, up to 400°C) | Good (up to 425°C) | Fair (acidic degradation products) | Good |
| 1.25Cr-0.5Mo | Good (high temp, overkill) | Excellent (＞400°C) | Good | Good |
| 316SS | Good (overkill for non-corrosive) | Good | Good (acid/corrosion) | Good |
| Duplex SS | Good | Good | Excellent (corrosion + abrasion) | Good |
| Cast iron | Fair (low temp only, ＜200°C) | NOT (high temp — brittle) | NOT | Good (cold oil) |
| Silicon carbide (seal) | Excellent (high temp + corrosion) | Excellent | Good (abrasion, brittle) | Good |
| Tungsten carbide (seal) | Good | Good | Excellent (coke abrasion) | Good |
| Carbon graphite (seal) | Good (up to 200°C) | NOT (＞250°C — oxidation) | NOT | Good |
| FFKM (Kalrez) seals | Excellent (up to 320°C) | Excellent (up to 320°C) | Excellent | Good |
| FKM (Viton) seals | Fair (up to 200°C) | NOT (＞200°C) | Fair | Good |
| PTFE seals | Good (up to 260°C) | Fair (＞260°C cold flow) | Good | Good |
| Graphite packing | Good (high temp, but leakage) | Good | Good | Good |
Critical: Mineral oil (＜350°C) = carbon steel WCB + FFKM/graphite + centerline OH2. Synthetic (350–400°C) = carbon steel/Cr-Mo + FFKM + centerline + high-temp seal (plan 32+53B) + low-NPSH (high VP). Degraded oil = 316SS/duplex + tungsten carbide + filtration. Cold oil = gear/screw (viscous, self-priming). All = centerline mounting (＞200°C) + high-temp seal + expansion tank + 100% standby + zero leakage + safety (fire/burn/toxic).
Common Problems and Solutions
Problem 1: Seal fails at 300°C. Standard FKM seal degrades. Solution: use high-temp seal (FFKM or graphite) with plan 32 flush (cool oil) + plan 53B barrier + jacketed seal chamber. API 610 OH2 centerline. Our high-temp seal arrangement handles 350°C+.
Problem 2: Synthetic oil pump cavitates (high VP). Dowtherm at 380°C = 10 bar VP — NPSH too low. Solution: low-NPSH API 610 OH2 (large eye, inducer). Flooded suction. Pressurized expansion tank. NPSH margin ＞3m. Our low-NPSH range prevents cavitation.
Problem 3: Pump misalignment (thermal expansion). Foot-mounted pump at 300°C — casing expands — misalignment — seal/bearing failure. Solution: use centerline-mounted API 610 OH2. Expansion joints in piping. Our centerline design maintains alignment.
Problem 4: Oil degrades (coke formation). Overheating + oxygen = oil degradation = coke fines = pump wear. Solution: don't exceed max film temp. Nitrogen blanket (expansion tank). Filtration (bypass). Oil analysis. Our filtration-ready pumps handle degraded oil.
Problem 5: Pump failure = process shutdown. Single pump fails — no heat — production loss. Solution: 100% standby API 610 OH2 (auto-start). Warm standby (bypass flow). Weekly exercise. Our redundant systems ensure continuous heating.
Selection Summary
- Main circulation (mineral ＜350°C): API 610 OH2 (carbon steel WCB, centerline, high-temp seal plan 32+53B, FFKM, low-NPSH, 100% standby)
- Main circulation (synthetic 350–400°C): API 610 OH2 (carbon steel/Cr-Mo, centerline, high-temp seal, low-NPSH for high VP, double seal, critical)
- Boiler/heater feed: OH2 or BB2 (carbon steel, 100–200°C return, large flow)
- Storage/filling (cold oil): Internal gear pump or screw pump (viscous cold oil, self-priming, positive displacement)
- Filtration loop: API 610 OH2 (hardened seal faces, 150–250°C, coke fines) or gear pump
- Asphalt/reactor/exchanger heating: API 610 OH2 (carbon steel, 200–350°C, large flow, centerline, VFD for temp control)
- Emergency/standby: Same as main (100% redundant, auto-start, warm standby)
- Critical: thermal oil = centerline mounting (＞200°C) + high-temp seal (plan 32 flush + 53B barrier + FFKM/graphite, NOT FKM ＞200°C) + low-NPSH (synthetic high VP) + expansion tank + oil degradation control (max temp, N2 blanket, filtration) + 100% standby (critical heating) + zero leakage + safety (fire/burn/toxic), mineral = carbon steel, synthetic = Cr-Mo + low-NPSH, cold = gear/screw
- Our API 610 OH2 and BB2 cover thermal oil circulation; gear and screw cover cold oil transfer. For thermal oil pump selection, talk to our engineers with your fluid type (mineral/synthetic), max temperature, flow, and system layout.