Both are Low Temperature Carbon Steel — but they serve very different temperature ranges. Specifying WPL6 when WPL3 is needed is a serious safety risk. Here is the complete guide.
ASTM A420 WPL6 and WPL3 are both Low Temperature Carbon Steel (LTCS) grades — but they have fundamentally different minimum service temperatures. Using WPL6 in a WPL3 application is a code violation that can lead to brittle fracture in service. The cost difference between the grades is small; the consequence of getting it wrong is not.
| Parameter | WPL6 | WPL3 |
|---|---|---|
| ASTM Standard | A420 WPL6 | A420 WPL3 |
| Minimum Design Temperature | -46°C (-50°F) | -73°C (-100°F) |
| Charpy Impact Test Temperature | -46°C | -73°C |
| Nickel Content | No requirement | 1.60–2.24% (mandatory) |
| Carbon Content (max) | 0.30% | 0.20% |
| Min Tensile Strength | 415 MPa | 415 MPa |
| Typical Application | Offshore, LPG, gas processing | LNG, liquid N₂, deep cryogenic |
| Cost vs WPB | ~15–25% premium | ~30–45% premium |
Most offshore design codes specify -46°C as the minimum design temperature for topside piping. WPL6 is the standard LTCS grade for offshore platforms in the North Sea, Middle East, and Southeast Asia.
LPG (propane/butane) is stored at temperatures down to -42°C. WPL6 is adequate for LPG service — the -46°C rating provides a safety margin over the minimum LPG storage temperature.
Arctic and sub-arctic gas processing plants specify WPL6 for outdoor piping exposed to ambient temperatures down to -46°C. Standard WPB (-29°C minimum) is inadequate for cold climate service.
LNG is stored and transported at -162°C (methane boiling point). LNG piping must be rated well below this — WPL3 at -73°C is the minimum for the warm end of LNG systems. The cold end requires 9% nickel steel or austenitic stainless.
Liquid nitrogen is at -196°C. WPL3 can be used for warm-end utility piping associated with nitrogen systems, but not for direct cryogenic liquid service.
Ethylene production involves temperatures down to -104°C in cryogenic separation. WPL3 is the minimum LTCS grade for the warmest sections of these systems.
⚠ Important: Always verify by impact test certificate
The only way to verify that a fitting is genuinely WPL6 or WPL3 is the impact test certificate showing test temperature and absorbed energy values. Request EN 10204 3.1 MTC with impact test results at the specified minimum temperature. PMI cannot distinguish WPL6 from WPB — only the impact test proves the LTCS properties.
We stock both with full Charpy impact test certificates. Tell us your minimum design temperature and we'll confirm the correct grade.