Metallurgical pump material selection play a critical role in Abrasive and Corrosive Service, delivering reliable fluid transfer and processing performance under demanding operating conditions. This article covers technical specifications including flow rate, head, pressure, materials, and seal options, key selection factors such as fluid properties and system layout, real-world engineering applications, frequently asked questions, and procurement recommendations to guide engineers and buyers.
Material selection is one of the most critical decisions in metallurgical pump specification. Pumps handle corrosive acids, caustic solutions, abrasive slurries, high-temperature fluids, and toxic chemicals. Wrong material selection leads to premature failure, safety hazards, and costly downtime. This guide covers material selection principles and recommendations for metallurgical pump applications.
Material Selection Factors
- Corrosion resistance: Fluid type, concentration, temperature, pH, chlorides, oxygen content
- Abrasion resistance: Solid particle size, shape, concentration, hardness, velocity
- Temperature: Operating temperature, thermal cycling, high-temp strength
- Pressure: Operating pressure, pressure rating, mechanical strength
- Fluid compatibility: Chemical reaction, stress corrosion cracking, hydrogen embrittlement
- Cost: Material cost, fabrication cost, maintenance cost, total cost of ownership
- Availability: Standard sizes, lead time, supplier capability
- Regulatory: FDA, 3A, ASME, API, NACE requirements
Common Pump Materials
Cast Irons
| Material | ASTM | Best For | Limitations |
|---|
| Gray cast iron | A48 Class 30 | Water, oil, concentrated acid (>90%) | Not for dilute acid, alkali, tensile strength low |
| Ductile iron | A536 65-45-12 | High-pressure, water, slurry housings | Limited corrosion resistance |
| Ni-Resist (austenitic CI) | A436 Type 2 | Caustic, mild acid, seawater | Not for strong acid, high temp |
| High-silicon iron | A518 Type 1 | Concentrated sulfuric acid, all temps | Brittle, not for impact, hard to machine |
Stainless Steels
| Material | UNS | Best For | Limitations |
|---|
| 304SS | S30400 | Water, mild acid, food, general | Not for chlorides > 500 ppm, strong acid |
| 316SS | S31600 | Moderate chloride, mild acid, caustic | Not for > 2000 ppm chloride, hot acid |
| 316L | S31603 | Welded components, low carbon | Same as 316, lower strength |
| Duplex 2205 | S31803/S32205 | High chloride, caustic, oil/gas | Not for > 250°C, strong reducing acid |
| Super duplex 2507 | S32750 | Very high chloride, seawater, FGD | Expensive, not for > 250°C |
| Alloy 20 (20Cb-3) | N08020 | Sulfuric acid, chemical processing | Not for halides, high cost |
| 254 SMO | S31254 | Very high chloride, seawater, bleaching | Expensive, not for strong reducing acid |
Nickel Alloys
| Material | UNS | Best For | Limitations |
|---|
| Hastelloy C-276 | N10276 | Strong acid, chloride, HF, oxidizing | Very expensive, not for > 1000°C |
| Hastelloy C-22 | N06022 | Welded, strong acid, chloride | Very expensive |
| Monel 400 | N04400 | HF, seawater, caustic, reducing acid | Not for oxidizing acid, ammonia |
| Inconel 625 | N06625 | High temp, acid, seawater | Expensive |
| Nickel 200 | N02200 | Hot caustic (NaOH), food | Not for acid, expensive |
Non-Metallic Materials
| Material | Best For | Temp Limit | Limitations |
|---|
| PTFE (Teflon) | Almost all chemicals, acid, caustic | 260°C | Cold flow, poor thermal conductivity |
| PFA | Similar to PTFE, better melt process | 260°C | Expensive |
| PVDF (Kynar) | Acid, halogens, solvents | 150°C | Not for strong caustic, ketones |
| PP (polypropylene) | Mild acid, caustic, water | 100°C | Not for solvents, low strength |
| PVC | Mild acid, caustic, water | 60°C | Low temp, low strength |
| Natural rubber | Slurry abrasion, water, mild acid | 80°C | Not for oil, solvent, ozone |
| Neoprene | Slurry, moderate chemical | 90°C | Not for strong acid, oil |
| Butyl rubber | Caustic, acid, phosphate | 120°C | Not for oil, solvent |
| Polyurethane | Slurry abrasion, fine particles | 70°C | Not for acid, high temp |
| Ceramic (Al₂O₃, SiC) | Very high abrasion, corrosion | 1000°C+ | Brittle, expensive, hard to repair |
Wear-Resistant Materials
| Material | Hardness | Best For | Limitations |
|---|
| 27% Cr white iron | 55-65 HRC | Slurry, coarse particles | Brittle, not for impact |
| High-chrome iron (15-28%) | 50-60 HRC | General slurry | Moderate toughness |
| Ni-Hard (Ni-Cr white iron) | 55-62 HRC | Slurry, moderate impact | Limited corrosion |
| Tungsten carbide | 88-92 HRA | Very high abrasion, nozzles | Very expensive, brittle |
| Ceramic (SiC, Al₂O₃) | 90+ HRA | Fine particle abrasion, corrosion | Brittle, impact sensitive |
| Rubber lining | — | Fine particle slurry (< 100 μm) | Temp < 80°C, not for oil |
Material Selection by Fluid
Sulfuric Acid (H₂SO₄)
| Concentration | Temp | Recommended | Avoid |
|---|
| < 10% | < 40°C | 316SS, PVDF | Cast iron, 304SS |
| 10-50% | 40-80°C | PVDF, PTFE, Hastelloy C | 316SS, cast iron |
| 50-90% | < 40°C | Cast iron, 316SS | — |
| 90-98% | < 40°C | Cast iron, carbon steel | 304SS (passivation issues) |
| 90-98% | 40-120°C | High-silicon iron, Alloy 20 | Cast iron (corrosion increases) |
Note: The 40-80% concentration range at elevated temperature is the most corrosive. Electrowinning electrolyte (15-20% at 50-65°C) falls in this range and requires PVDF, PTFE, or Hastelloy C.
Hydrochloric Acid (HCl)
- All concentrations and temperatures: PVDF, PTFE, Hastelloy C-276, or Monel (for reducing conditions)
- Never use 304SS or 316SS — rapid pitting and crevice corrosion
- For hot concentrated HCl: use PTFE lined or Hastelloy C
- Elastomers: PTFE, Kalrez (not EPDM or Buna-N)
Hydrofluoric Acid (HF)
- All concentrations: Monel 400, PTFE, or Hastelloy C
- Never use glass, silica, or ceramics — HF etches SiO₂
- Monel is preferred for anhydrous HF and aqueous HF
- Elastomers: PTFE or Kalrez (EPDM may work for dilute, cold)
- Magnetic drive pumps recommended — zero leakage
Sodium Hydroxide (NaOH / Caustic)
| Concentration | Temp | Recommended | Avoid |
|---|
| < 20% | < 80°C | 316SS, cast iron | Aluminum, zinc, brass |
| 20-50% | < 80°C | 316SS, Ni-Resist | Cast iron (stress cracking) |
| Any | 80-150°C | 316SS, Nickel 200, duplex | Carbon steel (caustic embrittlement) |
| Any | > 150°C | Nickel 200, Inconel 600 | 316SS (stress cracking) |
Note: Caustic embrittlement (stress corrosion cracking) occurs in carbon steel at high temperature + stress. Use stress-relieved carbon steel or stainless steel for hot caustic.
Slurry (Abrasive)
- Fine particles (< 100 μm): rubber-lined casing (natural rubber), 27% Cr impeller
- Coarse particles (> 100 μm): 27% Cr iron casing and impeller
- High velocity: ceramic or tungsten carbide wear parts
- Acidic slurry: 27% Cr (corrosion + abrasion) or rubber-lined with duplex shaft
- Large particles: open impeller, large passages
- Shaft: duplex 2205 (corrosion + strength)
Seawater / High Chloride
- Chlorides < 2000 ppm: 316SS
- Chlorides 2000-10000 ppm: duplex 2205
- Chlorides > 10000 ppm / seawater: super duplex 2507 or 254 SMO
- FGD water (10000-50000 ppm): super duplex 2507
- Elastomers: EPDM or PTFE (not Buna-N)
- Mechanical seal springs: Hastelloy C (316SS springs pit in high chloride)
High-Temperature (> 150°C)
- 150-250°C: 316SS, duplex, Alloy 20
- 250-400°C: Inconel 625, Hastelloy C, high-chrome steel
- > 400°C: Inconel, Hastelloy X, refractory alloys
- Elastomers: PTFE or Kalrez (EPDM limited to 150°C, Viton to 200°C)
- Mechanical seal: metal bellows, Plan 23 cooling
- Consider jacketing for heat tracing
Material Selection by Metallurgical Process
| Process | Fluid | Casing | Impeller | Shaft | Seal |
|---|
| Copper electrowinning | H₂SO₄ 15-20%, 50-65°C | PVDF/PTFE | PVDF/PTFE | 316SS | Magnetic drive |
| Copper SX organic | Kerosene + extractant | 316SS/CI | 316SS/bronze | 316SS | Mechanical (explosion-proof) |
| Alumina Bayer | NaOH 15%, 100°C | 316SS | 316SS | 316SS | Plan 23 |
| Red mud | Fe₂O₃ slurry, caustic | Rubber-lined | 27% Cr | Duplex 2205 | Expeller |
| Gold CIL | Ore slurry + cyanide | Rubber-lined | 27% Cr | Duplex 2205 | Expeller/double |
| Gold eluate | NaOH + cyanide, 100°C | Duplex/254 SMO | Duplex | Duplex | Double (Plan 53B) |
| Steel pickling | HCl/H₂SO₄, 50-80°C | PVDF/PTFE | PVDF/PTFE | 316SS | Magnetic drive |
| Steel descaling | Water, 150-250 bar | Cast steel/duplex | Stainless/duplex | Alloy steel | Mechanical (high pressure) |
| FGD slurry | Limestone/gypsum, pH 5 | Rubber-lined | 27% Cr | Duplex 2205 | Expeller/Plan 32 |
| FGD process water | High chloride, acidic | Super duplex 2507 | Super duplex | Super duplex | SiC/SiC, Hastelloy springs |
| Zinc plating | Acid/alkaline, 30-60°C | PVDF/316SS | PVDF/316SS | 316SS | Magnetic drive |
| Smelter acid plant | H₂SO₄ 93-98%, 80°C | High-silicon iron | High-silicon iron | Alloy 20 | Special acid seal |
Common Material Selection Mistakes
- Using 316SS for hot dilute sulfuric acid: Rapid corrosion. Use PVDF/PTFE/Hastelloy.
- Using 316SS for high chloride (FGD, seawater): Pitting and crevice corrosion. Use duplex/super duplex.
- Using cast iron for dilute acid: Rapid corrosion. Cast iron only for concentrated acid (>90%).
- Using EPDM for oil/petroleum: Swells and fails. Use Viton or Buna-N.
- Using Buna-N for hot caustic: Attacked. Use EPDM or PTFE.
- Using glass/ceramic for HF: HF etches SiO₂. Use Monel or PTFE.
- Using carbon steel for hot caustic: Caustic embrittlement. Use stress-relieved or stainless.
- Using rubber lining for coarse slurry: Tears. Use 27% Cr iron for coarse particles.
- Using 316SS springs in high chloride seals: Pitting. Use Hastelloy C springs.
- Ignoring velocity effects: Erosion-corrosion increases with velocity. Derate materials at high velocity.
Procurement Recommendations
- Provide complete fluid analysis: composition, concentration, temperature, pressure, pH, chlorides, solids, SG
- Require material test reports (MTR) for all wetted components
- Specify materials by ASTM/UNS designation, not generic names
- For critical service: require positive material identification (PMI) testing
- Specify elastomers per chemical compatibility — don't accept "standard"
- For slurry: specify lining material and thickness, impeller material grade. For example, a horizontal slurry pump with rubber-lined casing and 27% Cr impeller is standard for abrasive slurry service.
- For acid: specify concentration and temperature at pump location (not just tank). For hot dilute sulfuric acid, a high-temperature sulfuric acid pump with high-silicon iron construction may be specified.
- Include corrosion allowance (typically 3 mm for castings, 1.5 mm for stainless)
- For high chloride: specify PREN (pitting resistance equivalent number) minimum
- Require NACE MR0175 compliance if sour service (H₂S)
- For welded components: specify low-carbon grade (L) to prevent intergranular corrosion
- Verify supplier has material expertise and references for your application
- Consider total cost of ownership — cheaper material may fail faster
Related Industries
Material selection principles apply to all process industries: oil and gas (sour service, high temp), chemical manufacturing (acid, caustic, solvents), pharmaceutical (sanitary, CIP chemicals), food and beverage (cleaning chemicals), and power generation (FGD, high temp). The core principle — match material to fluid properties, temperature, pressure, and abrasion — is consistent across industries.