Stainless Steel Welded Pipes Manufacturer & Supplier | ASTM A312 / A778

Standards: ASTM A312 (welded, annealed) · A778 (welded, unannealed) · Grades: 304/L, 316/L, 321, 310S · Size: ½" to 24" NB

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A good weld is not a compromise; it is a manufacturing route with its own rules, and the rules are strict. Metinox Overseas is a stainless steel welded pipes manufacturer and supplier in Mumbai, covering ASTM A312 welded pipe for pressure duty and A778 for non-pressure work, ½" to 24" NB, shipped to buyers in India, the USA, the Middle East and Africa with 3.1 certification on every heat. For most general service, welded delivers the same grade at a meaningfully better price, which is why most of the stainless pipe in the world is welded. The grade family sits at Stainless Steel Pipes.

Where the route stops: thin-wall high-pressure design sometimes belongs to Stainless Steel Seamless Pipes on joint-efficiency grounds, and bores above 24" belong to Stainless Steel EFW Pipes. Between those edges, this page is where the budget stretches furthest.

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Types of Stainless Steel Welded Pipes

How Welded Stainless Pipe Is Made (No Filler, By Rule)

Stainless strip is roll-formed into a cylinder and the edges are fused longitudinally. Under A312, automatic welding is done without the addition of filler metal, so the seam is parent metal fused to parent metal, not a different chemistry laid into a groove. The pipe is then heat treated, tested and pickled the same as its seamless cousin. That no-filler rule matters: it is why a compliant A312 welded seam shares the corrosion behaviour of the pipe body instead of becoming its weakest line.

A312 Welded vs A778: Two Standards, Two Prices

ASTM A312 (welded)ASTM A778
ConditionSolution annealed after weldingAs-welded, not annealed
ServicePressure and corrosive process dutyNon-pressure: architectural, structural, drainage
TestingHydro or NDE on every pipeLighter regime, per standard
PriceHigher, and worth it under pressureLower, and right for what it is

The expensive mistake runs both directions. A778 in pressure service is an incident report waiting for a date; A312 on a handrail is money burned on an anneal the job never needed. Say the service and the correct standard follows.

How the Weld Is Tested

Each welded length goes through hydrostatic testing or nondestructive examination, exactly like seamless, and the seam rides through the same solution anneal and pickle. Chemistry certifies per heat, mechanicals per lot, and intergranular corrosion testing to ASTM A262 or PMI verification are added on request. The seam is not taken on trust anywhere in the chain, which is precisely why welded pipe can be specified with confidence.

Where Welded Is Exactly Right (and Where It Is Not)

  • Exactly right: utility and general process lines, water and CIP circuits, architectural and structural runs, and any cost-sensitive service inside the pressure envelope of the design.
  • Think twice: thin-wall high-pressure lines where the joint factor bites, severely cyclic duty, and specs that mandate seamless below a size threshold. That work sits with seamless.

The two routes argued out with numbers: seamless vs welded stainless steel pipe.

Welded SS Pipe Applications

  • Water & Wastewater: plant piping and headers, including African municipal utility packages.
  • Food, Dairy & Beverage: process and CIP distribution where welded 304 does the work at the right price.
  • Chemical & General Industry: utility and off-plot lines across Gulf and Indian sites.
  • Architecture & Structural: polished A778 for handrails, facades and interiors.
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SS Welded Pipe Testing, Certification & Export to USA, Middle East & Africa

Every order ships with an EN 10204 3.1 mill test certificate, heat-number traceable, 3.2 via BV, SGS or TUV on request. Metinox Overseas is ISO 9001 and PED certified, approved to SABIC, ADNOC, KNPC, EIL, IOCL and BPCL standards; see Quality Policy. Consolidations run from Mumbai to the USA, the Middle East and Africa, bundled and end-protected per Packing and Dispatch. Ex-stock dispatches in 7 to 14 working days; made-to-order sizes take 4 to 6 weeks.

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Stainless Steel Welded Pipes: Frequently Asked Questions

For most service, yes, and the standard is built to keep it that way: A312 welded pipe is fused without filler metal, annealed after welding, and hydro or NDE tested on every length. The seam becomes a design consideration mainly on thin-wall high-pressure lines, where the joint efficiency factor can favour seamless.

Heat treatment and intent. A312 welded pipe is solution annealed after welding and written for pressure and corrosive service. A778 is left as-welded and written for non-pressure work such as architectural and structural runs. Using A778 in pressure duty is the classic costly confusion, in both directions.

Every A312 welded pipe is hydrostatically tested or nondestructively examined, and the seam passes through the same anneal and pickle as the body. Nothing about the weld is taken on trust; that is what the standard exists to guarantee.

Yes, from Mumbai on regular consolidations with the full 3.1 documentation set. Gulf orders clear on SABIC, ADNOC and KNPC approvals, and African project cargo ships bundled and end-protected for the inland leg.

Yes. A778 pipe is supplied polished from 180 to 320 grit for handrails, facades and interiors, and the seam polishes with the body. For product-contact sanitary duty, tube to ASTM A270 is usually the correct call instead; tell us the job and we will route it.

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