The wetted parts of an API 610 OH2 pump — casing, impeller, shaft, wear rings, seal components — are the only parts that contact the process fluid. Material selection for these parts determines pump life, reliability, and safety. For hydrocarbon service, the main concern is temperature and pressure. For acidic service, the main concern is corrosion. For mixed service (hydrocarbon with acid contaminants), both matter.
This guide covers wetted part material compatibility for API 610 OH2 pumps in hydrocarbon and acidic service.
Wetted Parts: What Needs Material Selection
Each wetted part may use a different material. The casing holds pressure. The impeller generates head. The shaft transmits torque. The wear rings control internal recirculation. The seal contains the fluid.
| Part | Function | Material Criteria |
|---|---|---|
| Casing | Pressure containment | Corrosion resistance, pressure rating, weldability |
| Impeller | Hydraulic performance | Corrosion resistance, erosion resistance, castability |
| Shaft | Torque transmission | Strength, corrosion resistance, fatigue resistance |
| Wear rings | Internal clearance control | Wear resistance, galling resistance |
| Shaft sleeve | Shaft protection | Corrosion resistance, wear resistance |
| Mechanical seal | Shaft sealing | Face material compatibility, elastomer compatibility |
Hydrocarbon Service: Material Selection
Hydrocarbons (crude oil, gasoline, diesel, naphtha, LPG) are generally non-corrosive. The main material concerns are temperature, pressure, and sulfur content.
Low-Temperature Hydrocarbon (below 200°C)
Casing: Carbon steel (ASTM A216 WCB). Standard for hydrocarbon service up to 400°C. Cheap, weldable, good mechanical properties.
Impeller: Carbon steel or 12% chrome steel (CA15). 12% chrome provides better erosion resistance for fluids with solids (crude oil with sand).
Shaft: 4140 or 4340 alloy steel. High strength, good fatigue resistance.
Wear rings: 12% chrome steel (impeller ring) + cast iron (casing ring). Different hardness prevents galling.
Seal: Single mechanical seal, SiC/SiC faces, FKM (Viton) elastomer. FKM resists hydrocarbons well.
High-Temperature Hydrocarbon (200–400°C)
Casing: Carbon steel (WCB) up to 400°C. Above 400°C, use alloy steel (WC6, WC9) with chromium-molybdenum content for high-temperature strength.
Impeller: 12% chrome steel (CA15) or alloy steel. At high temperature, impeller material must retain strength.
Shaft: 4140 or 4340 alloy steel. At high temperature, check creep strength.
Seal: Single mechanical seal with Plan 23 (recirculation cooler). High-temperature fluid must be cooled before reaching the seal faces. Elastomer: FKM (up to 200°C) or FFKM (Kalrez, up to 300°C).
High-Sulfur Hydrocarbon (sour service)
Crude oil with high sulfur content (H₂S) causes sulfide stress cracking (SSC) in carbon steel. Material must be NACE MR0175 compliant.
Casing: Carbon steel with NACE MR0175 certification (controlled hardness, low sulfur content).
Shaft: 410 stainless or Inconel 625 (resists SSC). Standard 4140 is not suitable for sour service.
Seal: Special consideration — H₂S penetrates standard elastomers. Use FFKM (Kalrez) or PTFE encapsulated O-rings.
Acidic Service: Material Selection
Acidic fluids (sulfuric acid, hydrochloric acid, acidic process water) are corrosive. Material selection is based on acid type, concentration, and temperature.
Sulfuric Acid
Concentrated (93–98%): Carbon steel works — forms a protective iron sulfate film. But velocity must be below 1 m/s (higher velocity removes the film). Cast iron is also used.
Dilute (10–60%): Carbon steel does not work — the protective film does not form. Use 316L stainless (for low temperature) or PTFE-lined cast iron (for all temperatures). For high temperature, use Hastelloy C-276.
Impeller: Same material as casing for dilute acid. For concentrated acid, cast iron impeller is standard.
Seal: For concentrated acid, single mechanical seal with FKM elastomer. For dilute acid, double mechanical seal or magnetic drive (zero leakage). Our fluoroplastic magnetic drive pump is ideal for dilute acid service.
Hydrochloric Acid
HCl is one of the most corrosive acids. Carbon steel and 316L stainless are rapidly attacked.
Casing: PTFE-lined cast iron or PVDF plastic. No metal works for HCl at most concentrations.
Impeller: PTFE or PFA. Carbon-filled PTFE for mechanical strength.
Shaft: 316L stainless with PTFE sleeve (the sleeve contacts the acid, not the shaft).
Seal: Magnetic drive (sealless) is strongly recommended. HCl fumes are toxic and corrosive — zero leakage is essential.
Acidic Process Water (pH 2–6)
Mildly acidic water with low chloride content.
Casing: 316L stainless. Resists mild acid at room temperature.
Impeller: 316L stainless or duplex stainless (for higher chloride content).
Shaft: 316L stainless or 2205 duplex.
Seal: Single mechanical seal with SiC/SiC faces, EPDM elastomer (EPDM resists acids better than FKM).
Mixed Service: Hydrocarbon with Acid Contaminants
Some process fluids contain both hydrocarbon and acid (e.g., alkylation unit effluent, acid-containing crude). This is the most difficult material selection scenario.
Key principle: The material must resist both the hydrocarbon (temperature, sulfur) and the acid (corrosion). Often, no single material is ideal — a compromise is needed.
Casing: 316L stainless or duplex stainless. 316L resists mild acid and hydrocarbon. Duplex resists higher acid and chloride content.
Impeller: Duplex stainless (2205 or 2507). Higher strength and corrosion resistance than 316L.
Shaft: 2205 duplex or Alloy 20. Resists both acid and hydrocarbon.
Seal: Double mechanical seal with Plan 53B (barrier fluid). The barrier fluid protects the seal from both the hydrocarbon and the acid.
Material Compatibility Quick Guide
| Fluid | Casing | Impeller | Shaft | Seal |
|---|---|---|---|---|
| Crude oil (low sulfur, <200°C) | Carbon steel (WCB) | Carbon steel | 4140 alloy | Single, SiC, FKM |
| Crude oil (high sulfur, sour) | Carbon steel (NACE) | 12% chrome | 410 SS / Inconel | Single, SiC, FFKM |
| High-temp hydrocarbon (300°C) | Alloy steel (WC6) | 12% chrome | 4140 alloy | Single + Plan 23, FFKM |
| Conc. sulfuric acid (98%) | Cast iron / carbon steel | Cast iron | 316L sleeve | Single, SiC, FKM |
| Dilute sulfuric acid (10%) | PTFE-lined / 316L | PTFE / 316L | 316L sleeve | Double or magnetic drive |
| Hydrochloric acid | PTFE-lined / PVDF | PTFE / PFA | 316L + PTFE sleeve | Magnetic drive |
| Acidic water (pH 4) | 316L stainless | 316L stainless | 316L stainless | Single, SiC, EPDM |
| Hydrocarbon + acid (mixed) | Duplex 2205 | Duplex 2205 | Duplex 2205 | Double + Plan 53B |
Common Material Selection Mistakes
Mistake 1: Carbon steel for dilute sulfuric acid. The protective film does not form in dilute acid. The casing corrodes through in months. Right answer: 316L or PTFE-lined.
Mistake 2: 316L for hydrochloric acid. 316L dissolves in HCl within weeks. Right answer: PTFE-lined or PVDF.
Mistake 3: FKM elastomer for acidic service. FKM (Viton) is for oils and hydrocarbons. It swells and fails in acids. Right answer: EPDM for acids, FFKM for mixed service.
Mistake 4: Standard shaft for sour service. 4140 alloy steel suffers sulfide stress cracking in H₂S service. Right answer: 410 stainless or Inconel 625.
Mistake 5: Ignoring velocity effects. Concentrated sulfuric acid is fine in carbon steel at low velocity. At high velocity (>1 m/s), the protective film is removed and corrosion starts. Always check velocity when selecting material for concentrated acid.
For API 610 OH2 pump material selection and compatibility assessment, our API 610 OH2 pump range offers carbon steel, stainless, duplex, and alloy configurations. For material recommendation for your specific fluid, submit your fluid data — composition, concentration, temperature, and pressure.