What Is ASTM A358?
ASTM A358 is the standard specification for electric fusion welded (EFW) austenitic chromium-nickel stainless steel pipe for high-temperature service and general corrosive applications. It covers large-diameter stainless steel pipe manufactured from plate or sheet, welded with filler metal using SAW, GTAW, GMAW, or PAW processes.
Where ASTM A312 covers seamless and straight-seam welded stainless pipe up to moderate diameters, ASTM A358 extends stainless steel pipe availability to NPS 60+ by using EFW manufacturing from plate.
| Property | ASTM A358 |
|---|---|
| Pipe type | EFW (longitudinal seam) |
| Material | Austenitic stainless steel |
| Welding process | SAW, GTAW, GMAW, PAW (with filler) |
| Common grades | TP304, TP304L, TP316, TP316L, TP321, TP347 |
| Size range | NPS 8 to NPS 60+ |
| Wall thickness | Per ASME B36.19 (5S to 80S) or custom |
| Classes | 1, 2, 3, 4, 5 |
| Temperature | Cryogenic to 816°C (per grade) |
| Design code | ASME B31.3, B31.1 |
Grades and Mechanical Properties
| Grade | UNS | Cr (%) | Ni (%) | Yield min (MPa) | Tensile min (MPa) |
|---|---|---|---|---|---|
| TP304 | S30400 | 18-20 | 8-11 | 205 | 515 |
| TP304L | S30403 | 18-20 | 8-12 | 170 | 485 |
| TP316 | S31600 | 16-18 | 10-14 | 205 | 515 |
| TP316L | S31603 | 16-18 | 10-14 | 170 | 485 |
| TP321 | S32100 | 17-19 | 9-12 | 205 | 515 |
| TP347 | S34700 | 17-19 | 9-13 | 205 | 515 |
Class System
ASTM A358 uses a five-class system that is different from the ASTM A671/A672/A691 system.
| Class | Weld Type | Radiography | Key Requirement |
|---|---|---|---|
| 1 | Double-welded (ID + OD) | 100% RT | Full penetration from both sides |
| 2 | Single-welded with backing | 100% RT | Full penetration, backing ring or strip |
| 3 | Single-welded (no backing) | 100% RT | Full penetration, root pass quality critical |
| 4 | Single-welded or double-welded | Spot RT | Reduced examination |
| 5 | Single-welded or double-welded | None | No radiographic examination |
Class 1 (double-welded with 100% RT) is the standard requirement for critical process piping in refineries and chemical plants. The double-welded construction, where the root pass is welded from the pipe ID and the fill/cap passes from the OD, produces the highest quality weld seam.
ASTM A358 vs ASTM A312
| Feature | ASTM A358 | ASTM A312 |
|---|---|---|
| Manufacturing | EFW from plate | Seamless or welded (ERW/laser) |
| Size range | NPS 8 to NPS 60+ | NPS 1/8 to NPS 30 (typical) |
| Wall thickness | Heavier walls available | Standard schedules |
| Weld joint | Longitudinal, with filler | Autogenous or filler |
| Class system | 5 classes (weld quality) | None (single quality level) |
| Cost | Higher (for equivalent sizes) | Lower for standard sizes |
Applications
- Large-diameter stainless piping in chemical plants and petrochemical facilities
- Cryogenic piping in LNG plants (TP304L, TP316L)
- Flue gas desulfurization systems
- Urea and fertilizer plant piping (TP316L mod)
- Offshore platform topsides where corrosion resistance is required in large bore sizes
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