High-alloy austenitic stainless pipe, UNS N08904, for sulphuric and phosphoric acid service and moderate chloride service, with the specification question settled before the order.
- Standard: ASTM B673, ASTM B625, ASTM B677, ASME B36.19
- Grades: 904L (UNS N08904)
- Certificate: EN 10204 3.1 with every order, 3.2 on request
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Specifications
| Outer diameter | 1/8–24 in (10.3–610 mm) |
|---|---|
| Wall thickness | SCH 5S–SCH 80S, or by wall thickness |
| Schedule | 5S / 10S / 40S / 80S to ASME B36.19 |
| Size range | 1/8–24 in |
| Length | Quoted on the enquiry |
| Ends | Plain or beveled ends |
| Surface treatment | Pickled and passivated, or as specified |
| Manufacturing process | Seamless or welded (ERW / EFW) |
| Grade | 904L |
904L is a high-alloy austenitic stainless steel, UNS N08904, with molybdenum and copper in the composition. It is chosen where sulphuric and phosphoric acid service, or chloride service at moderate temperature, puts 316L outside its range, and where the project does not need a nickel alloy. One thing about it is worth settling before the pipe is ordered: which specification it now belongs to.
Where 904L earns its cost, and where it does not
904L is a corrosion grade, not a strength grade. The table below is the decision, service by service.
| Service | Why 316L is not enough | Where 904L stands | When the project goes further |
|---|---|---|---|
| Sulphuric acid | 316L corrodes across the concentration and temperature range where 904L is normally specified | The standard choice at moderate concentration and temperature | Above the range 904L holds, the project moves to a nickel alloy |
| Phosphoric acid and mixed acid service | 316L corrodes | Commonly specified | Where fluorides or chlorides are also present, the corrosion study decides |
| Chloride service, seawater and brine | 316L pits and suffers crevice attack | Suits chloride service at moderate temperature | Higher temperature or higher chloride moves the project to duplex 2205 or 2507, or to a 6% molybdenum grade |
| The CRA layer of a clad or lined line pipe | — | One of the corrosion resistant alloy grades used as the layer | The layer grade is set by the corrosion study, not by the backing steel |
| High strength requirement | — | Not the answer: 904L is austenitic and is not a high strength grade | Duplex, or a precipitation hardening grade |
Composition and mechanical limits are set by the governing specification, and the mill certificate is issued against it.
The specification question: ASTM moved 904L out of the nickel alloy standards
UNS N08904 is classified as a stainless steel rather than a nickel alloy, because iron is the largest element by mass in its composition. ASTM has applied that definition, and the nickel alloy specifications that once listed 904L no longer do: the current scope of the nickel alloy plate, sheet and strip specification (ASTM B625) and of the nickel alloy seamless pipe and tube specification (ASTM B677) both record that UNS N08904, previously in those specifications, was recognised instead as a stainless steel.
In practice this means a purchase specification that still writes “904L to B677” or “904L to B625” is quoting a scope the grade has left. It is worth settling with the project before the order, because it decides which specification the mill certificate is issued against, and a certificate to the wrong document is a documentation problem on delivery even when the pipe itself is sound.
What we do: the order is made and certified to the specification named on the enquiry. If an enquiry names B677 or B625 for a 904L line, we raise it before pricing rather than ship a certificate that does not match.
What we supply
904L is supplied in the same range as the rest of the stainless line, seamless or welded as the project permits.
| Form | Outside diameter | Wall | Where it is specified |
|---|---|---|---|
| Seamless 904L pipe | 1/8–24 in (10.3–610 mm) | SCH 5S–SCH 80S, or by wall thickness | Process service, and wherever the project restricts welded pipe |
| Welded 904L pipe (ERW or EFW) | 1/8–24 in (10.3–610 mm) | SCH 5S–SCH 80S, or by wall thickness | Larger sizes in thinner walls, where the project permits welded pipe |
| 904L fittings and flanges | Quoted to the size on the enquiry | Matched to the pipe | Where the line is specified in 904L throughout |
Sizes outside the table are quoted on the enquiry. Stainless schedules follow ASME B36.19 where the project uses the S series: SCH 5S, 10S, 40S and 80S are defined, and there is no SCH 20S or 60S.
What to state on the enquiry
Five things decide whether a 904L enquiry can be priced without a question back.
- Form and size: seamless or welded, outside diameter and wall, or the schedule
- Quantity, and the length or length range
- The specification the certificate is to be issued against, and whether the project has named a nickel alloy document for the grade
- Surface and finish: pickled and passivated, or as specified
- Inspection and documents: the certificate type, and whether third party inspection is required before shipment
Frequently asked questions
Is 904L a stainless steel or a nickel alloy?
By the ASTM definition it is a stainless steel: iron is the largest element by mass in the composition, and grades of that kind were recognised as stainless steels rather than nickel alloys. That is why the current scope of the nickel alloy pipe and tube specification no longer lists UNS N08904.
Is 904L the same as 316L with more molybdenum?
No. 904L is a higher alloy austenitic grade with molybdenum and copper additions, and it is specified for acid and chloride service where 316L is outside its range. The two are not interchangeable at the same size and wall: the grade is part of the specification, and the pipe and the fittings on the same line have to match.
Can 904L be welded?
Yes. It is welded with matching consumables and a controlled heat input, as with the other austenitic grades. Where the pipe will be welded, say so on the enquiry so the consumables and any post weld treatment are quoted together with the pipe.
When should the project use duplex instead of 904L?
Duplex 2205 or 2507 is normally the choice where higher strength, or resistance to chloride stress corrosion cracking, is the driver. 904L is a corrosion grade for acid service and moderate chloride service. The corrosion study decides, and it is better settled before the order than at the mill.
Where to go next
904L is one grade in the stainless line: the range, the forms and how a stainless order is fixed are on Stainless Steel Pipe. The grade most often specified below it is ASTM A312 TP316L pipe. Where 904L is used as a corrosion resistant layer rather than as solid pipe, the construction is covered on CRA clad and lined pipe. Where the line calls for higher strength instead of higher alloy, the alternative is ASTM A790 duplex pipe.
Materials
- High-alloy austenitic stainless steel with molybdenum and copper
Typical applications
- Sulphuric acid service
- Phosphoric acid and mixed acid service
- Chloride and seawater service at moderate temperature
- CRA layer on clad and lined line pipe
- Chemical process piping
Inspection & testing
- Dimensional and hydrostatic test
- Pickling and passivation
- PMI on request
- MTC to EN 10204 3.1, 3.2 on request
| Packaging | Sea-worthy export packing. |
|---|---|
| MOQ | On request |
| Lead time | Made to order; confirmed on quotation |
Payment: T/T 30% deposit with the balance before shipment; L/C at sight also accepted. Final terms are confirmed on the quotation.
How we supply: sourced through partner mills; the producing mill is named on the quotation. How we supply sets out who is accountable for the order.
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