Corrosion-Resistant Pipes for Chemical and Petrochemical Plants
Recommended Pipe & Tube Materials
Chemical plants handle sulfuric, hydrochloric, phosphoric and nitric acids, caustics, chlorides and organic solvents, often at high temperature and pressure. A pipe that performs well in one medium can fail quickly in another, so selection has to be based on the actual process conditions. This guide summarizes how stainless steel, duplex and nickel alloy pipes are matched to common chemical services.
Key Requirements
- Resistance to uniform, pitting, crevice and intergranular corrosion
- Resistance to stress corrosion cracking (SCC) from chlorides and caustics
- Stability at process temperature and under thermal cycling
- Weldability and availability of fittings and flanges in the same alloy
- Compliance with pressure codes such as ASME B31.3
Material Guide by Medium
| Medium | Commonly used pipe materials | Notes |
|---|---|---|
| Nitric acid | 304L, 316L, high-Si stainless | Oxidizing acid; chromium content is key |
| Sulfuric acid (dilute to moderate) | 904L, Alloy 20 (N08020), Alloy 825 | Concentration and temperature are critical |
| Phosphoric acid | 316L, 904L, Alloy 825 | Impurities (chlorides, fluorides) increase attack |
| Hydrochloric acid | Alloy C276, Alloy B-3, Alloy 59 | Very few materials tolerate HCl; stainless steel is generally unsuitable |
| Hydrofluoric acid | Alloy 400 (Monel) | Classic material for HF service |
| Caustic soda (NaOH) | Nickel 200/201, Alloy 600, 316L (low temp) | Nickel and nickel alloys handle hot caustic |
| Chloride-bearing process streams | Duplex 2205, 2507, 6Mo, Alloy 625 | Avoid 304/316 at elevated temperature (SCC risk) |
| Mixed, oxidizing and reducing acids | Alloy C276, Alloy C22 | Versatile choice for upset conditions |
This table is a general starting point. Always verify against iso-corrosion data and your process conditions.
Where Each Material Fits
316L / 317L: general process lines, utilities, and moderately corrosive services. 317L adds molybdenum for better pitting resistance.
904L and Alloy 20: sulfuric acid service, plus phosphoric acid and organic acid production. Alloy 20 was developed specifically for sulfuric acid applications.
Duplex 2205 / 2507: chloride-containing streams, cooling water, and where high strength allows thinner, lighter pipe.
Nickel alloys (C276, C22, 625, 825, 400): the answer where stainless steel and duplex reach their limits: strong acid mixtures, wet chlorine, hot chlorides, and reducing acids.
Standards Commonly Specified
- ASTM A312 (austenitic stainless pipe), ASTM A790 (duplex pipe)
- ASTM B677 (904L), ASTM B729 (Alloy 20), ASTM B423 (Alloy 825)
- ASTM B622 / B619 (C276, C22), ASTM B165 (Alloy 400), ASTM B444 (Alloy 625)
- ASME B36.19 / B36.10 for dimensions, ASME B31.3 for process piping design
Practical Selection Tips
- Get accurate process data: concentration, temperature, impurities, flow velocity and whether conditions are continuous or intermittent
- Consider upset conditions such as acid carry-over, cleaning cycles and shutdown condensation
- Choose low-carbon (L) or stabilized grades for welded systems to avoid sensitization
- Use matching filler metals and solution-anneal or pickle after fabrication where required
- Email: info@duplex-stainless-steel.com
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Frequently Asked Questions
Q1: What is the best pipe material for sulfuric acid?
It depends on concentration and temperature. Alloy 20 and 904L are common for moderate concentrations; nickel-molybdenum alloys and special materials are used for hotter or more demanding conditions.
Q2: Why is Hastelloy C276 pipe so widely used in chemical plants?
C276 resists a wide range of oxidizing and reducing chemicals, including wet chlorine, hypochlorite and mixed acids, and is highly resistant to pitting and SCC. It is a common choice when process conditions are variable or severe.
Q3: Can duplex stainless steel replace 316L in chemical plants?
In many chloride-containing services, yes: duplex offers higher strength and better resistance to chloride SCC. However, it is not a universal replacement, particularly for some acids and temperatures above roughly 300 °C.
Q4: Can you supply pipes with fittings and flanges in the same alloy?
Yes, we can supply matching pipes, fittings and flanges. Please include your full bill of materials in the inquiry.
Request a Quote for Chemical Process Pipes
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