ASTM A358

USED FOR:

Electric-fusion-welded austenitic stainless steel pipe intended for corrosive or high-temperature service where welded stainless steel construction is required.

A358 governs electric-fusion-welded austenitic stainless steel pipe. It is commonly used for large-diameter applications where welded construction is preferred. The specification defines weld examination requirements through different classes, which may be considered in conjunction with the applicable design code requirements for pressure design.

RELATED STANDARDS:

• Sibling specs: ASTM A312 covers both seamless and welded austenitic stainless pipe together under one specification but without A358’s formalized joint-class/examination-linked efficiency system, making A312 the more common choice for small-to-mid diameter pipe where seamless is available. ASTM A409 covers welded large-diameter stainless pipe for low-to-moderate pressure and general corrosion-resistant service, generally used where pressure requirements are lower than what A358 is intended to qualify for. ASTM A790 covers welded and seamless duplex/super-duplex stainless pipe, used instead of A358 once the material family shifts from austenitic to duplex for chloride stress corrosion cracking resistance.
• Design code that invokes it: ASME B31.3 may reference ASTM A358 as an acceptable material specification for stainless steel process piping. Application in pressure vessels shall be verified against the applicable ASME BPVC requirements and material acceptance criteria.
• Dimensional standard that pairs with it: ASME B36.19M (stainless steel pipe) defines OD and wall thickness/schedule data for A358 pipe, consistent with other stainless pipe products; larger, non-standard diameters common to A358 applications are sometimes governed by project-specific or fabricator-specific dimensional data rather than a strict B36.19M schedule.

GRADE / TYPE RANGE:
A358 covers austenitic stainless steel grades including TP304/304L, TP316/316L, TP321, TP347 and other grades listed in the applicable ASTM A358 edition,  since the distinguishing feature of A358 is the welded manufacturing/examination system rather than a unique set of grades.

The “L” grades again trade a modest reduction in elevated-temperature strength for lower carbon content and reduced sensitization risk during welding and post-weld service, which matters more in A358 than in many other stainless specs given the inherently welded nature of the product.

Stabilized grades (321, 347) are commonly selected for the higher end of A358’s temperature range where long-term carbide precipitation is a concern. The real “grade-like” variable in A358, though, is the Class designation (Class 1 through Class 5 in various editions), which reflects the extent of radiographic examination performed on the weld seam. The A358 class designation defines the extent of weld examination and acceptance requirements. The applicable design code shall be used to determine the weld joint efficiency for pressure design calculations.

This is arguably a more consequential selection than the base metallurgical grade for A358 specifically.

DESCRIPTION:
A358 covers pipe manufactured by welding formed plate into pipe using an electric-fusion-welding process, generally without filler metal for thinner sections and with filler metal for heavier wall sections, the required heat treatment condition shall be in accordance with ASTM A358 requirements for the applicable grade, manufacturing route, and product condition.

The standard’s core structure revolves around defining Classes 1 through 5, each tied to a specific extent of radiographic (or in some classes, no) examination of the longitudinal weld seam, with the corresponding joint efficiency factor to be applied in the purchaser’s pressure design calculation, this RT-to-joint-efficiency linkage is the defining engineering feature of the standard.

Testing requirements include tensile testing and weld examination requirements specified by ASTM A358. Additional tests, including intergranular corrosion testing, may be required when specified by the purchaser. Marking requirements identify manufacturer, grade, heat number, class, and the NDE extent performed, since the class designation itself carries direct engineering consequence and must be traceable on the pipe.

TYPICAL INDUSTRY USE:
Common in large-diameter stainless steel piping in petrochemical and chemical process plants, power generation (particularly large stainless steam or process lines), and any application requiring big-bore corrosion-resistant pipe where seamless production isn’t practical or economical.

IMPORTANT NOTES:

• We frequently see A358 confused with A312 on large-diameter welded stainless pipe requisitions. When a project specification requires a defined weld examination class or specific weld acceptance requirements for welded stainless steel pipe, ASTM A358 is often selected. ASTM A312 does not use the same class designation system.

• Additionally requirements under A358 typically involve upgrading the RT class (e.g., requiring full RT, Class 1,  instead of a lower class default) to achieve joint efficiency of 1.0, which directly reduces required wall thickness, we always double-check with the piping design/stress engineer which class the wall thickness calculation assumed before accepting mill certs, since receiving pipe with a lower class than assumed in design is a real (and expensive) risk.

• IGC (intergranular corrosion) testing is available as a supplement similar to A312, and we recommend confirming this explicitly is required on the PO for services where sensitization from the welding process itself is a concern, since the base standard doesn’t universally mandate it across all grades.

• NACE MR0175/ISO 15156 qualification follows the same logic as A312, not inherent to the base standard, and in cold-worked or high-hardness conditions (less common for A358 given its typically larger, thinner-wall, non-cold-worked product form) hardness limits should still be checked for sour, chloride-bearing service.

• A358 material often has longer delivery times and fewer qualified suppliers than A312 given the more specialized large-diameter EFW process and mandatory post-weld solution annealing of big-bore sections, we recommend mentioning this early on projects with large stainless process piping, since procurement timelines are frequently underestimated relative to smaller-bore seamless alternatives.