Cross-system equivalents
Cross-system grades are nearest counterparts, not drop-in substitutes. Chemistry and mechanical envelopes overlap but are not identical — where a design code names a grade, order that grade. Final selection should be confirmed by your project engineer against the governing code.
| Standard system | Grade designation |
|---|---|
| ASME / ASTM | A234 WP11 / WP22 / WP91 |
| EN / DIN | 13CrMo4-5 · 10CrMo9-10 · X10CrMoVNb9-1 |
| JIS | STPA23 / STPA24 |
| GOST | 15ХМ / 12Х1МФ |
| GB | 15CrMo / 12Cr1MoV |
Where this grade belongs
- Boiler, superheater and main steam piping in thermal power plant
- Heat recovery steam generators (HRSG)
- Refinery hydroprocessing and catalytic reforming units
- Any line where sustained metal temperature exceeds the carbon steel creep limit
Where it does not
The failures we see most often are not bad material — they are the right material in the wrong service.
- Skipping post-weld heat treatment — Cr-Mo grades harden in the heat-affected zone. PWHT is not optional, and hardness survey results are normally a hold point.
- Mixing grades in one line — WP11, WP22 and WP91 have different filler metal and PWHT requirements. Positive material identification on every piece is standard practice for a reason.
- Ambient-temperature service — There is no benefit and considerable cost. Carbon steel is the correct choice below the creep range.
What we supply in ASTM A234 WP11 / WP22 / WP91
Forms: Butt-weld elbows, tees, reducers and caps; forged flanges in the matching A182 F11 / F22 / F91 grades
Size range: DN15 – DN900 typical, larger to enquiry
Documentation available
- EN 10204 3.1 material test certificate traceable to the heat number
- PMI (positive material identification) on every piece as standard practice
- Heat treatment charts and hardness survey results supplied with the lot
- PED 2014/68/EU with 4.3 material appraisal
- Third-party witness of heat treatment by SGS, BV or TÜV
Frequently asked
What is the difference between WP11, WP22 and WP91?
Chromium and molybdenum content, and therefore allowable stress at temperature. WP11 is 1.25Cr-0.5Mo, WP22 is 2.25Cr-1Mo, WP91 is 9Cr-1Mo-V. WP91 is the grade used in supercritical and ultra-supercritical steam service.
Do chrome-moly fittings need post-weld heat treatment?
Yes. The heat-affected zone hardens during welding, and PWHT is required to restore toughness and relieve residual stress. Hardness survey after PWHT is normally a project hold point.
Why is PMI required on Cr-Mo fittings?
Because a WP11 and a WP22 fitting are visually identical, and installing the wrong one in a high-temperature line is a safety issue rather than a paperwork issue. Positive material identification confirms each piece by composition.
Related grades
- ASTM A234 WPB — Carbon steel butt-weld fittings
- ASTM A403 WP321 / WP347 — Stabilised austenitic stainless steel
- ASTM A105 — Carbon steel forgings — flanges and forged fittings
Full cross-reference across all families: Technical Guide § 2 — Material Grade Equivalents. Pressure class and schedule conversion: § 3 — Pressure Ratings & Pipe Schedules.