Stainless Steel Pipe

Stainless steel pipe is bought for what it resists rather than for the pressure it carries. The range runs from 304 through 316L, 321, 347 and 310S to the duplex grades, supplied seamless or welded, and the decision that fixes an order is which standard and which grade the service calls for. This page sets out what we supply, how the specification is fixed, and where the detail on each grade sits.

What we supply

Stainless pipe is supplied seamless or welded, in the austenitic grades and in duplex where the project permits it. The table gives the dimensions the grade pages already quote, so the enquiry can be checked against them before it is priced.

Lengths are supplied SRL 5.8 m, DRL 11.8 m or a fixed length. Ends are plain, beveled or threaded. Surface condition is pickled, annealed and pickled, bright annealed, polished or shot blasted, and it is a separate line on the order rather than an assumption.

Which standard the enquiry belongs to

The standard decides the test regime, so it is worth fixing before the grade. The two that are most often confused are ASTM A312 and ASTM A269: A312 is pressure pipe, with a hydrostatic and eddy current regime behind it; A269 is general service tube, and it is quoted to the standard the project names.

Where the project names a standard, that standard governs. We do not substitute a standard we hold stock against for one the project asked for, and the certificate follows the standard on the order.

How the specification is fixed

The decisions come in a particular order, and taking them the other way round is what produces a second quotation.

1. The service condition – the fluid, the chloride content, the operating temperature, and whether H2S or CO2 is present. This is what rules grades in or out before strength is considered.
2. The grade family – 304 or 304L for benign chemical and general industrial duty; 316 or 316L where chlorides are present, including seawater, brine and coastal atmospheres; 321 or 347 where the service is in the sensitising range; 310S for high temperature oxidation; duplex where the austenitic grades do not hold.
3. The form – seamless or welded, after checking whether the project restricts welded pipe for that service.
4. The size – outside diameter together with the schedule or the wall thickness. Stainless schedules follow ASME B36.19M, whose S schedules are thinner than the matching ASME B36.10M carbon steel schedules.
5. The finish and the tolerance – pickled, annealed and pickled, bright annealed, polished to a stated roughness, or shot blasted.
6. The test route and the documents – what is tested, and which certificate type the project accepts.

What to state on the enquiry: the standard and grade, the manufacturing route, the outside diameter and wall or schedule, the length and end finish, the surface condition, the test route, the quantity and the destination port. With those fields the order can be priced without another round of questions.

The finish and the test route are separate decisions

Finish decides how the surface behaves in service, not only how the pipe looks. A pickled or annealed-and-pickled surface removes the heat tint and the depleted layer left by welding; a bright annealed surface is specified where cleanliness or a low roughness matters; a polished surface is specified against a stated roughness rather than as “smooth”.

The test route is the second separate decision. Hydrostatic testing and eddy current examination are the routine routes on A312 pipe. Where the service is in the sensitising range, intergranular corrosion testing to ASTM A262 is specified alongside the grade. Positive material identification verifies the actual heat against the grade on the certificate, and it is a different check from a mill test certificate. The certificate itself is to EN 10204 3.1, or 3.2 where an inspector independent of the mill has to issue it – see mill test certificate for what each type has to show.

One boundary is worth stating plainly: the certificate is issued against the heat the pipe came from, so a test added after the heat is rolled becomes a re-test or a new heat, not a line on the same certificate.

Where stainless is the wrong answer

Stainless is not automatically the better pipe, and four of the cases where it is the wrong answer come up often.

Nickel is the main cost driver across the grades, and the grade and the form are the two decisions that move it most. Pricing follows the specification that comes out of the assessment above.

Frequently asked questions

Is stainless pipe ordered the same way as carbon steel pipe?

By outside diameter and wall, yes, but the schedule system differs. Stainless steel schedules are defined in ASME B36.19M, and the S suffix marks them: SCH 10S is thinner than SCH 10, and SCH 40S is thinner than SCH 40. Not every schedule has an S equivalent – SCH 5S, 10S, 40S and 80S are defined. The pipe schedule chart lists the wall for each size and schedule.

Can welded stainless pipe replace seamless?

ASTM A312 permits both, and welded pipe is supplied as-welded or cold worked to meet the same mechanical requirements, so for most corrosive service a properly made and solution annealed weld performs equivalently to seamless. Welded pipe is the economical choice in larger sizes and thinner walls. Some end users and specifications still restrict stainless pipe in critical service to seamless, and where that restriction exists it is stated on the enquiry rather than assumed by the mill.

What is the difference between A312 and A269?

A312 covers austenitic stainless pipe for pressure and corrosive service, with the hydrostatic and eddy current testing that goes with it. A269 covers general service tube, where the requirement is dimension and surface rather than a pressure regime. If the project names one of them, that one applies; ordering A269 because it is available when the project asked for A312 is a substitution, not a saving.

Do you supply duplex stainless pipe?

Yes – duplex and super duplex, the 2205 and 2507 grades, where the project permits them. Whether they are permitted is a corrosion assessment rather than a preference, and it turns on the H2S partial pressure, temperature, pH and chloride content together. The assessment inputs are set out on the sour service page.

Do you supply 904L stainless pipe?

Yes, where the corrosion assessment calls for it. 904L pipe (UNS N08904) sits between 316L and the 6% molybdenum grades: it is specified for sulphuric and phosphoric acid service and for chloride service at moderate temperature. One point is worth settling early, because it decides the certificate rather than the pipe: the grade is classified as a stainless steel rather than a nickel alloy, so the nickel alloy specifications no longer list it.

Download Stainless Steel Pipe data sheet (PDF) One page: supply range, grades and key sizes, what to state on the enquiry, and the inspection documents that come with the order. The standard is the governing document.

Where to go next

• ASTM A312 stainless steel pipe – the specification, and how to choose between 304 and 316
• ASTM A312 TP304 / TP316 / TP316L – chemistry, mechanical properties and inspection for each grade
• Boiler and heat exchanger tube – the A213 tube range
• Stainless steel butt weld fittings – fittings matched to the pipe grade
• Pipe schedule chart – wall thickness for every size and schedule
• Sour service – where duplex and the higher alloys are required
• Steel pipe – the carbon, alloy and coated pipe lines