904L is the stainless that took the copper trick from the nickel alloys, and it uses it to handle sulphuric acid. Metinox Overseas supplies SS 904L pipe to ASTM B677 and A312, UNS N08904, seamless and welded, with 3.1 certification and export lanes to the USA, the Middle East and Africa. It is a high-alloy super-austenitic stainless with deliberate copper, high nickel and molybdenum and very low carbon, built for dilute sulphuric and phosphoric acid and chloride-bearing process streams that pit ordinary 316. It sits at the top of the austenitic stainless ladder, one step before the grade turns into a nickel alloy. The stainless family sits at Stainless Steel Pipes.
The one comparison every 904L buyer runs is against 254 SMO, and the answer turns on acid versus chloride. For that decision see our 254 SMO Pipe page, cross-referenced below. And where the duty needs more nickel than a stainless can carry, the step up is Incoloy 825 Pipes & Tubes.
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Table of content
- What 904L Is: The Copper-Bearing Acid Stainless
- 904L vs 254 SMO: Acid or Chloride?
- SS 904L Chemistry & Mechanical Properties
- 904L Pipe Standards, Sizes & Forms
- SS 904L Pipe Applications & Export to USA, Middle East & Africa
- Stainless Steel 904L Pipes Related Types
- Explore Related Ranges
- SS 904L Pipe: Frequently Asked Questions
What 904L Is: The Copper-Bearing Acid Stainless
The copper is the defining element. Between 1 and 2 percent copper gives 904L its specific resistance to sulphuric and phosphoric acid, the same reason Incoloy 825 carries copper, and it is what separates 904L from the 6-molybdenum grades that are built for chloride instead. Around 25 percent nickel confers strong resistance to chloride stress corrosion cracking that 316 lacks, roughly 4 to 5 percent molybdenum adds pitting resistance for a PREN in the mid-30s, and the very low carbon keeps the grade resistant to sensitization when welded. It is a genuinely acid-first stainless, which is a rarer thing than it sounds. The grade below is SS 316/316L Pipe.
904L vs 254 SMO: Acid or Chloride?
This is the fold that resolves most 904L enquiries, and the two grades are genuinely different tools despite looking similar on a datasheet.
| 904L (N08904) | 254 SMO (S31254) | |
|---|---|---|
| Molybdenum | About 4 to 5% | About 6 to 6.5% |
| Copper | 1 to 2% (deliberate) | 0.5 to 1% |
| Nitrogen | Low | 0.18 to 0.22% (adds strength and PREN) |
| PREN | About 34 to 36 | About 43 |
| Best at | Dilute sulphuric and phosphoric acid | High chloride, seawater, pitting resistance |
| Strength | Standard austenitic level | About twice 300-series yield |
The rule: if the main threat is reducing acid, especially sulphuric, 904L's copper gives it the edge. If the main threat is chloride pitting, especially in seawater or brine, 254 SMO with its higher molybdenum, nitrogen and PREN is the safer choice. Both are super-austenitic; they simply optimize for opposite enemies.
SS 904L Pipe Applications & Export to USA, Middle East & Africa
- Sulphuric & Phosphoric Acid Plant: acid piping, coolers and storage, an Indian and African fertilizer lane.
- Flue Gas Desulphurisation: scrubber circuits handling acid chlorides, USA and India.
- Chemical & Pharmaceutical: acidic process streams that overwhelm 316.
- Pulp & Paper: bleaching and acid recovery.
- Oil & Gas: selected chloride and acid service.
Every order ships with an EN 10204 3.1 certificate; see Quality Policy. Consolidations run from Mumbai to the USA, the Middle East and Africa per Packing and Dispatch. Made to order, typical delivery 4 to 8 weeks.
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SS 904L Pipe: Frequently Asked Questions
Dilute sulphuric and phosphoric acid and chloride-bearing process streams that pit ordinary 316. Its deliberate copper gives specific sulphuric acid resistance, its high nickel confers chloride stress corrosion cracking immunity, and its low carbon keeps it weldable. It is common in acid plant, FGD scrubbers, pulp and paper and pharmaceutical process lines.
What they optimize for. 904L carries deliberate copper for sulphuric and phosphoric acid resistance, with a PREN around 34 to 36. 254 SMO carries more molybdenum and nitrogen for chloride pitting resistance, with a PREN around 43. If the threat is reducing acid, choose 904L; if it is chloride pitting or seawater, choose 254 SMO. Both are super-austenitic stainless steels.
A super-austenitic stainless steel, though with around 25 percent nickel it sits near the boundary. It is specified and priced as a high-alloy stainless, one step below nickel alloys like Incoloy 825, which take over where more nickel is needed.
For sulphuric and phosphoric acid resistance specifically. Copper improves performance in reducing acids, which is why both 904L and the nickel alloy Incoloy 825 carry it deliberately. It is the element that makes 904L an acid-first grade rather than a chloride-first one.
Yes, made to order with 3.1 documentation, PMI on request. Fertilizer and acid plant in India and Africa, and FGD and chemical work in the USA and the Gulf, are the regular lanes, shipped from Mumbai.
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