Raw Materials · Stainless Steel Products
Seamless pipe is formed from a pierced billet and drawn or rolled to size, so the wall runs unbroken from end to end. There is no weld to radiograph, no bead to clean out of a hygienic line, and no strip of heat-affected metal behaving differently from the rest of the tube — which is why pressure, fatigue and product-contact duty so often specify it.
Four families cover the range we quote most often. The grade is chosen for the environment rather than the price list, because the difference between them only shows up once the pipe is in service.
The general-purpose austenitic grade: strong enough for structural and pressure work, easy to cut, bend and weld, and the cheapest seamless option where chlorides are not in the picture.
Structural and mechanical pipe, water and process lines, general fabrication
Two to three percent molybdenum raises pitting and crevice resistance, which is why 316 is the grade specified wherever the media carries chlorides. The L grade keeps carbon low so welds and their heat-affected zone do not sensitise.
Food and pharmaceutical lines, chemical process, marine and sanitary service
A mixed austenitic-ferritic structure with roughly twice the yield strength of 304 and resistance to chloride stress corrosion cracking. 2507 pushes pitting resistance further for severe seawater duty.
Offshore and seawater systems, brine and chloride process lines, high-pressure service
Seamless hollow section with continuous walls around the corners, used where a flat face has to carry a bracket and the section is part of the structure rather than just a conduit.
Machine frames, handrails and balustrades, structural and architectural workNeed a grade not shown here? The A312 and A269 families also include TP310S, TP317L, TP321/321H, TP347/347H and TP316Ti, and the duplex family runs to S32750. Send the standard and the grade designation — including the L or H suffix — and we will confirm what the mills can supply with the certificate you need.
Seamless is bought against a standard, so the table starts there: each row is a different test regime and tolerance set, not just a different label. Anything outside the window is still worth asking about.
Typical manufacturing window; the grade, wall and test regime on your order are confirmed before anything is cut.
Swipe the table sideways to see the size window and grades →
| Application | Standard | Size window | Grades |
|---|---|---|---|
| Austenitic pipe, general service | ASTM A312 / ASME SA312 | OD 6.0 – 914.0 mm, WT 0.5 – 88 mm | TP304, TP304L, TP304H, TP310S, TP316, TP316L, TP316Ti, TP317L, TP321, TP321H, TP347, TP347H |
| Austenitic tube, general service | ASTM A269 | OD 6.0 – 50.8 mm, WT 0.8 – 10.0 mm | TP304, TP304L, TP304H, TP310S, TP316, TP316L, TP316Ti, TP317L, TP321, TP321H, TP347, TP347H |
| Boiler, superheater and heat-exchanger tube | ASTM A213 / ASME SA213 | OD 6.0 – 50.8 mm, WT 0.8 – 10.0 mm | TP304, TP304L, TP304H, TP310S, TP316, TP316L, TP316Ti, TP317L, TP321, TP321H, TP347, TP347H |
| Duplex tube, general service | ASTM A789 / A789M | OD 19.0 – 60.5 mm, WT 1.2 – 5.0 mm | S31803, S32205, S32750 |
| Duplex pipe | ASTM A790 / A790M | OD 3/4" – 10", WT SCH5S – SCH80S | S31803, S32205, S32750 |
| Mechanical tubing | ASTM A511 | OD 6.0 – 50.8 mm, WT 1.8 – 10.0 mm | MT304, MT304L, MT304H, MT316, MT316L, MT317L, MT321, MT321H, MT347 |
| Pressure purposes, European designation | EN 10216, DIN 17456 / 17458 | OD 6.0 – 914.0 mm, WT 0.5 – 88 mm | 1.4301, 1.4307, 1.4401, 1.4404, 1.4541, 1.4571, 1.4432, 1.4462 |
Seamless is not automatically the better tube. These four points are what you are paying for — and the last one is where the argument usually ends.
Without a longitudinal weld there is no seam to radiograph, no weld bead to clean out of a hygienic line, and no difference in corrosion behaviour between one side of the circumference and the other.
A homogeneous wall handles cyclic pressure and mechanical loading more predictably than a welded tube of the same dimensions, which is why pressure and dynamic duty tends to specify seamless.
Seamless covers heavy wall and small bore in one route. Where a welded tube stops at the thickness its strip can be formed from, seamless keeps going.
Seamless costs more per metre and moves slower than welded. On thin walls, large diameters and architectural work, welded is usually the better answer, and we will say so.
Most material disputes start with a standard or a suffix that was never written down. We settle those four questions before a price is quoted.
A312, A269, A213 and A511 are not interchangeable: they differ in test regime and tolerance. The standard goes on the quote, because it decides the mill route.
TP316L is not TP316, and 321H is not 321. Low-carbon and high-carbon variants behave differently after welding, so the suffix is part of the requirement.
Outside diameter and wall have to exist as a combination, not as two separate numbers. We check the pair before quoting rather than after.
Hydrostatic or non-destructive testing to the standard, mill certificate with the heat number, then saw cutting to the length on the drawing.
Seamless pipe turns up wherever a seam would be the weakest point — in pressure, in a cleaning regime, or in a fatigue cycle that a welded tube would eventually notice.
Process and utility lines where the media, the pressure or the consequence of a leak puts a welded seam out of consideration.
Product-contact lines that are cleaned in place: a continuous bore with no weld bead is easier to clean and easier to prove clean.
Tube bundles, superheaters and economisers, specified to A213 where temperature and pressure cycling decide the tube's life.
Small-bore and heavy-wall tube for sensing lines, manifolds and hydraulic circuits, where a consistent bore matters more than the cost per metre.
Need a seamless grade, wall or standard that is not listed? Send the specification, quantity and any certification requirement and we will come back with what we can supply.
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