Technical knowledge
904L stainless steel for sulphuric acid piping
Where 904L fits in sulphuric acid service: composition, concentration and temperature limits, comparison with 316L and duplex, and specification notes for flanges and fittings.
Composition and properties
| Item | Value | Significance |
|---|---|---|
| Chromium | 19.0 - 23.0 % | Oxidising acid resistance |
| Nickel | 23.0 - 28.0 % | Acid resistance, stress corrosion resistance |
| Molybdenum | 4.0 - 5.0 % | Pitting and crevice resistance |
| Copper | 1.0 - 2.0 % | Sulphuric acid performance |
| Carbon | 0.02 % maximum | Sensitisation control |
| Typical PREN | About 35 | Comparable with duplex 2205 |
The service window in plain terms
904L performs well in sulphuric acid up to moderate concentration at moderate temperature, and in phosphoric acid where fluoride levels are low. It also handles organic acids and many salt solutions. It is not a substitute for Hastelloy in hot concentrated acid, and it does not resist hydrochloric acid.
How 904L compares with the alternatives
- Against 316L. Much better in acid and better in chloride, but significantly more expensive.
- Against duplex 2205. Similar PREN but lower strength and better toughness; 2205 is usually cheaper and stronger for water service.
- Against Incoloy 825. 825 has the higher nickel content and broader acid range, particularly with chlorides present.
- Against 254SMO. 254SMO offers higher pitting resistance for chloride dominated duty but no copper for reducing acid.
Questions about this topic
Is 904L suitable for seawater?
It resists pitting reasonably well but is not immune to crevice corrosion in warm or stagnant seawater. Duplex 2205, super duplex 2507 or a nickel alloy are better choices for immersed service.
What is the maximum sulphuric acid concentration for 904L?
It depends strongly on temperature and on the presence of oxidising or reducing contaminants. Use isotherm data from the alloy producer for the specific combination rather than a single concentration limit.
Can 904L be welded without filler metal changes?
Use an over alloyed filler such as a high molybdenum nickel base consumable, and control heat input. The weld metal, not the parent metal, is usually the limiting region in acid service.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email demi@nickel-alloy.com or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.