Choosing the wrong material for a chemical-service pump is the most expensive engineering mistake we see in Indian process plants. A pump correctly sized for flow and head but specified in SS316 for a dilute HCl service will pit through within months, leaking acid, contaminating product, and forcing emergency replacement — all because the upfront cost of upgrading to PFA-lined seemed unjustified.
This guide covers the practical Material of Construction (MOC) decisions for the seven most common chemical pump duties in Indian industry, with reference data for the major fluids and a decision tree for when to escalate from SS316 to Alloy 20, Hastelloy, or PFA.
Reading a Chemical Compatibility Chart
Manufacturer compatibility charts use a rating system — "A" (excellent / no attack), "B" (minor effect / acceptable for short-term), "C" (moderate attack / not recommended), "D" (severe / fails). Most engineers know to pick "A" rated materials — but the real skill is reading between ratings.
Three pitfalls:
- Concentration matters as much as identity. Sulfuric acid attacks cast iron at 50% concentration but the same cast iron passivates above 95%. Hydrochloric acid attacks SS316 at any concentration. Always specify both chemical and concentration.
- Temperature can flip a rating. SS316 handles 35% sulfuric acid at room temperature ("B" rating), but at 60 °C the same fluid is "D" — severe pitting. Always specify operating temperature, not just chemical.
- Trace contaminants kill. A "pure HCl" service in a chlor-alkali plant might also contain ferric chloride and dissolved oxygen — these turn HCl from manageable to lethal for most metals. Field corrosion never matches a chemical compatibility chart based on pure reagent.
The Six Material Tiers, Ranked by Cost
Tier 1: Cast Iron / Ductile Iron
Default for clean water, raw sewage, low-pH drainage. Surprisingly, also valid for concentrated sulfuric acid (above 93%) where it forms a protective FeSO4 layer. Cost reference: 1x. Avoid for chlorides, dilute acids, or anything alkaline above pH 11.
Tier 2: SS304 / SS304L
Fine for nitric acid (any concentration), most organic acids, mild alkalis up to pH 12, food-grade water. Fails on chlorides above 200 ppm due to pitting and stress-corrosion cracking. SS304 is rarely the right answer for industrial chemical pumps in India because of widespread chloride contamination. Cost reference: 2x.
Tier 3: SS316 / SS316L (workhorse)
The default for chemical-service centrifugal pumps in chemical, pharma and specialty applications. Molybdenum content (2-3%) gives chloride resistance up to ~1000 ppm at room temperature. Handles most organic acids, dilute mineral acids, alkalis to pH 13, sea water (with caution). Cost reference: 2.5x.
SS316L (low carbon) is preferred for welded and complex castings to prevent sensitization. SS316Ti (titanium-stabilized) is used for high-temperature service above 425 °C.
Tier 4: Duplex Stainless (CD4MCu, 2205, Super Duplex)
~50% Cr, with austenite + ferrite microstructure. Better chloride resistance than SS316, twice the strength. Common in offshore, chlor-alkali brine, and seawater service. Cost reference: 3-4x. Most Indian chemical plants jump from SS316 to Alloy 20 or Hastelloy — duplex is less commonly specified locally.
Tier 5: Alloy 20 (Carpenter 20Cb-3)
Designed specifically for sulfuric acid service in the difficult middle range (20-95% concentration, 30-70 °C). Adds copper to the SS chemistry to passivate against H2SO4. Cost reference: 6x. Use for concentrated phosphoric, sulfuric mid-strength, mixed sulfate processes.
Tier 6: Hastelloy C-276 / C-22
The premium nickel-molybdenum-chromium alloy. Resists all common acids, alkalis, oxidizers and chlorides up to high temperature. The default when SS316 fails and PFA isn't an option (e.g., abrasive slurry, high-velocity service). Cost reference: 12x. Use cautiously — often PFA-lined at 5x is a better answer for the same service.
Tier 7: PFA-Lined / PTFE-Lined
A metallic shell (typically ductile iron or carbon steel) lined internally with 3-5 mm of PFA fluoropolymer. The PFA contacts the fluid — and PFA is essentially inert to all common acids, alkalis, chlorides, and most solvents from -60 to +200 °C. Richter PFA-lined pumps from Target Marketing handle the most aggressive service in Indian chemical industry. Cost reference: 5x. Limits: not for abrasive slurries (lining wear), not above 200 °C, slight permeability to small-molecule gases at high pressure.
Decision Matrix by Common Indian Chemical Service
| Fluid | Concentration | Temp | Recommended MOC | Avoid |
|---|---|---|---|---|
| Hydrochloric acid (HCl) | Any | Any | PFA-lined (Richter) | SS304, SS316, even Hastelloy at high HCl |
| Sulfuric acid (H2SO4) | <5% | <30 °C | SS316L | Cast iron, SS304 |
| Sulfuric acid (H2SO4) | 20-95% | 30-70 °C | Alloy 20 | SS316, cast iron |
| Sulfuric acid (H2SO4) | >95% | <40 °C | Cast iron (paradox — passivates) | SS316, Hastelloy |
| Sulfuric acid (oleum) | 105-110% | Any | Cast iron or Hastelloy C | Most other metals |
| Nitric acid (HNO3) | 0-65% | <60 °C | SS304L or SS316L | Ferrous, copper alloys |
| Phosphoric acid (H3PO4) | <75% | <80 °C | SS316L or Alloy 20 | Cast iron, SS304 |
| Caustic soda (NaOH) | <50% | <90 °C | SS316L or PFA-lined | Aluminum (severe attack) |
| Sodium hypochlorite (NaOCl) | 10-15% | Any | PFA-lined or Hastelloy C | SS316, copper alloys |
| Hydrofluoric acid (HF) | <48% | <30 °C | PFA-lined only | Glass, Hastelloy (yes), most metals |
| Brine / saltwater | 3-25% | <60 °C | SS316L, Duplex 2205 | SS304, cast iron |
| Dye liquor (textile) | Mixed | <90 °C | SS316L or PFA-lined or PP/PVDF | SS304, cast iron |
| Pharmaceutical intermediate | Various solvents | 10-80 °C | SS316L electropolished or PFA-lined | Anything that contaminates |
| Methanol / ethanol / IPA | Any | <65 °C | SS316L (with ATEX motor) | Aluminum, copper |
| Edible vegetable oil + hexane | Mixed | 40-65 °C | SS316L (with explosion-proof drive) | Cast iron (food contamination) |
The Three Modes of Corrosion to Worry About
1. Uniform Corrosion (the easy case)
The whole wetted surface attacks evenly. Predictable, slow, manageable by adding "corrosion allowance" to thickness. Most chemical compatibility charts predict this well.
2. Pitting / Crevice Corrosion (the killer)
Localised attack creates pits or crevices that can perforate a 5 mm casing in weeks. Driven by chlorides, oxidizing conditions, and stagnant zones. The reason SS304 fails on borderline service even when bulk corrosion rate looks acceptable. Pitting is the #1 failure mode in Indian chemical plants.
3. Stress Corrosion Cracking (SCC)
Tensile stress + corrosive environment + susceptible alloy = sudden brittle failure. SS304 and SS316 in chloride service above 60 °C are classic SCC victims. Detection is hard until a casing splits. Switch to duplex, Hastelloy, or non-metallic if SCC is a risk.
The PFA-Lined Trump Card
For most aggressive Indian chemical services — chlor-alkali, specialty acids, mixed waste streams, pharmaceutical intermediates — PFA-lined pumps are the most cost-effective answer. Why?
- Inert to virtually all acids, alkalis, chlorides — one MOC handles the entire process spectrum.
- Mag-drive variants eliminate seal leakage entirely — mandatory for hazardous fluids under emissions regulations.
- 5x SS316 cost — cheaper than Hastelloy (12x) and lasts longer because no localised pitting.
- Same casing can handle process changes (retrofit a PFA pump from HCl to caustic without replacing).
Limitations to know: PFA-lined is not for high-velocity abrasive slurry, not for service above 200 °C, and the price premium is hard to justify for benign water-based service.
How to Specify Materials in a Pump Inquiry
When you submit a pump inquiry to Target Marketing, give your application engineer this minimum information:
- Fluid name and CAS number (if specialty)
- All concentration ranges (operating, startup, cleaning)
- All temperature ranges (operating, washdown, ambient)
- Solids content (concentration, particle size, hardness)
- Any oxidizers, chlorides, or trace contaminants
- Process pH excursions during cleaning / batch changes
- Hazard classification (toxic, flammable, ATEX zone)
With this data, our engineering team produces a material recommendation backed by manufacturer compatibility data, cross-checked with field performance from similar Indian installations.
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Talk to an Engineer WhatsApp UsFrequently Asked Questions
Which pump material is best for hydrochloric acid?
For HCl at any concentration, PFA-lined or PTFE-lined is preferred — Richter mag-drive PFA pumps handle pH 0-14 fluids up to 200°C with zero corrosion. Never use SS316 or SS304 for HCl service.
What is the difference between SS304 and SS316?
SS316 contains 2-3% molybdenum which provides much better chloride pitting resistance than SS304. For any chloride service above 200 ppm, SS316 is the minimum. SS316L is preferred for welded constructions to prevent sensitization.
When should I choose Hastelloy over stainless steel?
Hastelloy C-276 is the go-to alloy when SS316 fails — hot oxidizing acids, mixed acids, hypochlorites, high chlorides. Costs 4-6x more than SS316 but lasts 5-10x longer in aggressive service.
What are the limits of PFA-lined pumps?
PFA-lined pumps handle pH 0-14, all common acids/alkalis, up to 200°C. Limits: permeable to some gases, not abrasion-resistant for slurries, 50-80% premium over metallic. Not for steam-cleaning above 150°C.
What about Alloy 20 — when is it the right choice?
Alloy 20 is specifically formulated for sulfuric acid in the 20-95% range and 30-70°C. For dilute or room-temperature service, SS316L often works. For hot concentrated sulfuric, Alloy 20 is the answer at 2-3x SS316 cost.
