Article
Seamless pipe is often seen as the premium product, but welded stainless pipe is used in huge quantities and is the only practical choice for large diameters. Understanding the main welded routes helps buyers specify the right product at the right price.
How welded pipe is made
- Strip-formed pipe – stainless strip is roll-formed into a tube and welded longitudinally, usually by TIG, plasma or laser, often without filler metal. This is typical for ASTM A312 welded pipe in small and medium sizes.
- Plate-formed pipe (EFW) – plate is pressed or rolled into a cylinder and joined by electric fusion welding, usually with filler metal. This is the ASTM A358 route for larger sizes and heavier walls.
ASTM A312 welded vs ASTM A358 EFW
| Point | A312 welded | A358 EFW |
|---|---|---|
| Starting material | Strip or coil | Plate |
| Filler metal | Usually none | Usually used |
| Typical sizes | Small to medium | Medium to very large, heavy walls |
| Weld examination | Hydro or electric test | Depends on class (radiography options) |
ASTM A358 classes
| Class | Welding | Radiography |
|---|---|---|
| 1 | Double welded with filler | 100% |
| 2 | Double welded with filler | None |
| 3 | Single welded with filler | 100% |
| 4 | Single welded, filler in root pass on outside | 100% |
| 5 | Double welded with filler | Spot radiography |
Class 1 is the most commonly specified for critical service.
When welded pipe is the right choice
- Large diameters where seamless is unavailable or very costly
- Thin-wall SCH 5S and 10S lines in water, food and chemical plants
- Low and moderate pressure process lines
- When uniform wall thickness and good concentricity are important
Ordering
Pipe 18" SCH 10S, ASTM A358 TP316L Class 1, EFW, bevelled ends, EN 10204 3.1
Frequently asked questions
What does EFW mean?
Electric fusion welded – pipe made from plate and welded with an electric fusion process, usually with filler metal.
Which A358 class is most common?
Class 1: double welded with filler metal and 100% radiography.
Is welded stainless pipe acceptable for process plants?
Yes, when it meets the specification and class required by the piping design.
Key takeaways
- A312 welded pipe is strip-formed; A358 is plate-formed EFW.
- A358 Class 1 = double welded, 100% RT.
- Welded pipe is the practical choice for large, thin-wall lines.
Need these products?
Sawariya Metal Industries supplies stainless steel pipes, flanges and buttweld pipe fittings from Mumbai to buyers in India and overseas. Send your size, grade, standard and quantity through our enquiry form and we will reply with a clear quotation and the test documents you need. You can also browse our stainless steel pipes, flanges and buttweld fittings.