ASTM A358 vs A312 vs EN 10217-7: Which Standard Fits Your Large Diameter Stainless Welded Pipe?

Three Standards, Three Different Jobs

ASTM A312, ASTM A358 and EN 10217-7 all end up as stainless steel pipe on a project, but they were written for different products. ASTM A312 covers seamless, welded and heavily cold worked austenitic stainless pipe for high temperature and general corrosive service. ASTM A358 covers electric fusion welded (EFW) austenitic stainless pipe, which is the normal route for large diameter and heavy wall sizes. EN 10217-7 is the European pressure purpose standard for welded stainless steel tubes and works in metric outside diameters.

Scope and Size Range

ASTM A312 runs from NPS 1/8 to NPS 48, but the welded part of that range is concentrated in the smaller sizes; above roughly NPS 16 it is rarely the economical answer. ASTM A358 starts at NPS 6 and goes to NPS 48 with wall thickness ordered by schedule or weight class, which is why large diameter stainless steel welded pipe is almost always specified to A358. EN 10217-7 is ordered by outside diameter in millimetres following the EN ISO 1127 series, so a European specification will state 610 mm or 1,016 mm rather than 24 inch or 40 inch.

Welding and Heat Treatment

A358 is built around a longitudinal or helical seam welded from plate or coil, with filler metal permitted, and the finished pipe is either solution annealed or supplied in the as welded condition depending on the class ordered. A312 welded pipe is normally cold worked after welding, which is practical only at small diameters. EN 10217-7 leaves heat treatment to the grade and the delivery condition agreed in the order, and expects the manufacturer to hold qualified welding procedures to EN ISO 15614-1 or equivalent.

The Part Buyers Usually Miss: Classes and Test Categories

A358 is split into classes 1, 2, 3, 4 and 5, and the difference is heat treatment plus the proportion of weld length that is radiographed or ultrasonically tested. Class 1 is the strict end of the range with all welds examined and heat treatment applied; lower classes reduce or drop that examination. EN 10217-7 uses test categories and inspection options, so the same tube can be supplied with nothing beyond the routine pressure test or with full non destructive testing of the longitudinal weld. Writing A358 or EN 10217-7 without the class or test category is the single most common gap we see in incoming purchase orders.

Which Standard to Put on the PO

For a European refinery or water project following EN codes, specify EN 10217-7 with the grade, outside diameter, wall thickness, test category and inspection option. For a US coded project, or a project where the EPC works in inches, specify ASTM A358 with the class, and add ASTM A240 for the plate chemistry and ASTM A262 practice for intergranular corrosion testing if the service is aggressive. Specify ASTM A312 only where the size and wall fall inside its practical welded range and the end user accepts cold worked welded pipe.

Mistakes That Cost Real Money

Three show up again and again. Ordering A312 at 1,200 mm OD and then discovering no qualified mill will cold work it. Ordering A358 Class 3 for a wet chloride service and finding the weld examination is not what the inspector expected. Ordering EN 10217-7 without stating the test category, then arguing about who pays for the additional radiography. All three are settled at the quotation stage if the specification is written properly.

How SHIWANG PIPE Quotes These Orders

Our works in Qingzhou and Yangzhou form large diameter stainless welded pipe on 8,000 tonne, 15 metre presses with an annual capacity of 200,000 tonnes, and we produce to ASTM, ASME, EN, DIN and GB specifications. Duplex, super duplex, 904L, 321, 347H and 310S are all available with third party inspection and a stamped EN 10204 3.1 certificate. Send the standard, class or test category, size, grade, quantity and inspection requirement and the quotation comes back complete.

Related reading on this site: large diameter thick wall stainless steel welded pipe, extra large diameter stainless steel welded pipe, and stainless steel welded pipe for oil and gas.