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ASTM A234 WP12 Buttweld Fittings
ASTM A234 WP12 Buttweld Fittings
Why does WP12 exist when WP11 already does? The chemistries almost overlap. Chromium runs 0.80 to 1.25 percent against WP11's 1.00 to 1.50, both grades temper from a 620 degree minimum, and both sit in the same band of moderate elevated temperature service, which makes the distinction genuinely fine. The honest answer is that WP12 is slightly leaner, slightly cheaper, and survives in specifications and plants that standardised on it long ago. It has two classes; WP11 has three. Solitaire Overseas manufactures and exports A234 WP12 buttweld fittings from India in Class 1 and Class 2.
Technical Data
WP12 Compared With WP11
| WP12 | WP11 | |
|---|---|---|
| Chromium | 0.80 - 1.25% | 1.00 - 1.50% |
| Molybdenum | 0.44 - 0.65% | 0.44 - 0.65% |
| Silicon | 0.60% max | 0.50 - 1.00% |
| Classes | Class 1, Class 2 | Class 1, Class 2, Class 3 |
| Min tempering temperature | 620 C | 620 C |
| Service band | Moderate elevated temperature | Moderate elevated temperature, slightly higher margin |
Practical guidance. Where a specification names WP12, supply WP12. Where a project is being specified fresh and either would serve, WP11 is the more widely stocked grade with a third class available if higher strength is needed later. Where an existing plant standardised on WP12 decades ago, continuing with it avoids mixed-grade welds across the site. None of these is a metallurgical argument; the deciding factor is usually the specification and what is already in the ground.
WP12 Chemistry and Classes
| Element | Range |
|---|---|
| Carbon | 0.05 - 0.15% (Cl 1), 0.05 - 0.20% (Cl 2) |
| Manganese | 0.30 - 0.61% |
| Phosphorus | 0.045% max |
| Sulfur | 0.045% max |
| Silicon | 0.60% max |
| Chromium | 0.80 - 1.25% |
| Molybdenum | 0.44 - 0.65% |
WP12 Chemistry and Classes
| Class | Tensile min | Yield min |
|---|---|---|
| Class 1 | 380 MPa (55 ksi) | 220 MPa (32 ksi) |
| Class 2 | 485 MPa (70 ksi) | 275 MPa (40 ksi) |
Where WP12 Is Used
- Moderate elevated temperature steam piping, in plants specified around the grade.
- Petrochemical process lines, at temperatures above carbon steel's range.
- Boiler and heater connecting piping, in the intermediate temperature sections.
- Maintenance and replacement work, on plant originally built to WP12, avoiding a mixed-grade weld.
Supplied as elbows, tees, reducers, caps and pipe bends.
| Item | Detail |
|---|---|
| Standard | ASTM A234 / ASME SA234 WP12 |
| Dimensional | ASME B16.9, ASME B16.28 |
| Classes | Class 1, Class 2 |
| Chromium | 0.80 - 1.25% |
| Size range | NPS 1/2 inch to 48 inch |
| Matching pipe | ASTM A335 P12 |
| Certification | EN 10204 3.1. PMI and NDE on request |
Matching pipe: ASTM A335 P12 pipes. Closest alternative: WP11 fittings.
Heat Treatment
- Minimum tempering temperature 620 C, shared with WP1 and WP11.
- A useful alternative route. Fittings of Grades WP1, WP12 Class 1 or WP12 Class 2, whether hot formed or cold formed, may be given a final heat treatment at 650 C. This option is not available on the higher alloy grades and can simplify manufacture.
- NDE timing is flexible. As with WP11, examination of welds may be performed either before or after forming, unlike WP5, WP9, WP22 and WP91 where it must follow forming.
- PWHT by thickness. Required once wall thickness exceeds the code threshold, rather than mandatory in all cases as on WP22 and WP91.
Frequently Asked Questions
Chromium content and class availability, and both differences are small. WP12 carries 0.80 to 1.25 percent chromium against WP11's 1.00 to 1.50, and WP12 comes in two classes where WP11 has three. Molybdenum and minimum tempering temperature are the same. In practice the deciding factor is usually what the specification names or what the plant was originally built to, rather than a metallurgical distinction. See our WP11 fittingspage.
Yes. ASTM A234 allows fittings of Grades WP1, WP12 Class 1 and WP12 Class 2, whether hot formed or cold formed, to be given a final heat treatment at 650 degrees C. This route is not available on the higher alloy grades and can simplify manufacture on the leaner chrome-moly fittings.
ASTM A335 P12. Matching the fitting grade to the pipe grade keeps chemistry consistent through the welded joint and avoids creating a dissimilar-metal weld that would need a separately qualified procedure.
Request a Quote
Send your fitting type, size, schedule and class, and we will confirm availability, certification and lead time. If your specification allows either WP11 or WP12, tell us and we will advise on availability.