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ASTM A234 WP9 Buttweld Pipe Fittings
ASTM A234 WP9 Buttweld Pipe Fittings
If five percent chromium resists sulfidation, nine percent resists it better. That is the whole argument for WP9 over WP5, and on a refinery unit running high sulphur crude it is argument enough. Everything else about the two grades runs close together: the same role for molybdenum, the same 675 degree minimum tempering temperature, the same 217 HBW hardness ceiling, and the same position outside the power plant creep ladder that WP11 and WP22 occupy. Chromium is the variable. Solitaire Overseas manufactures and exports A234 WP9 buttweld fittings from India in Class 1 and Class 3. Below: how WP9 differs from WP5 and where it is specified.
Technical Data
Choosing Between WP5 and WP9
| WP5 | WP9 | |
|---|---|---|
| Chromium | 4.0 - 6.0% | 8.0 - 10.0% |
| Molybdenum | 0.44 - 0.65% | 0.90 - 1.10% |
| Sulfidation resistance | Good | Better, resistance rises with chromium |
| Max hardness | 217 HBW | 217 HBW |
| Min tempering temperature | 675 C | 675 C |
| Cost | Lower | Higher |
| Specify it when | Moderate sulphur environment | High sulphur crude, or where WP5 service life has proved inadequate |
Note that WP9 also carries roughly double the molybdenum of WP5. So the step from WP5 to WP9 is not purely a chromium increase, it raises high temperature strength as well. Where a unit is being upgraded because fittings are thinning faster than the design allowed, WP9 addresses both the corrosion rate and the mechanical margin.
WP9 Chemistry and Mechanical Classes
| Element | Range |
|---|---|
| Carbon | 0.15% max |
| Manganese | 0.30 - 0.60% |
| Phosphorus | 0.030% max |
| Sulfur | 0.030% max |
| Silicon | 1.00% max |
| Chromium | 8.0 - 10.0% |
| Molybdenum | 0.90 - 1.10% |
| Class | Tensile min | Yield min |
|---|---|---|
| Class 1 | 415 MPa (60 ksi) | 205 MPa (30 ksi) |
| Class 3 | 520 MPa (75 ksi) | 310 MPa (45 ksi) |
Where WP9 Is Used
- High sulphur crude processing, where WP5 corrodes faster than the design life allows.
- Hydroprocessing and hydrotreating, elevated temperature units handling sulphur-bearing feed.
- Catalytic reforming and cracking, high temperature process piping.
- Furnace and heater transfer lines, in aggressive refinery service.
- Upgrades and replacements, where existing WP5 components have shown unacceptable wall loss.
Supplied as elbows, tees, reducers, caps and pipe bends.
| Item | Detail |
|---|---|
| Standard | ASTM A234 / ASME SA234 WP9 |
| Dimensional | ASME B16.9, ASME B16.28 |
| Classes | Class 1, Class 3 |
| Chromium | 8.0 - 10.0% |
| Max hardness | 217 HBW |
| Size range | NPS 1/2 inch to 48 inch |
| Matching pipe | ASTM A335 P9 |
| Certification | EN 10204 3.1. PMI, hardness and NDE on request |
Matching pipe: ASTM A335 P9 pipes. Lower chromium alternative: WP5 fittings.
What the Standard Requires
- Maximum hardness 217 HBW. Shared with WP5 and WPR. A cap rather than a floor, guarding against environmental cracking in refinery service.
- Minimum tempering temperature 675 C. Shared with WP5 and WP22, above WP11 and WP12 at 620 C.
- NDE after forming. Welds must be examined after forming, since forming can open defects that were acceptable beforehand.
- Supply condition. Full-annealed, isothermal-annealed, or normalized and tempered.
- Hardness testing. Minimum two pieces per batch or continuous run.
Frequently Asked Questions
Where the sulphur environment is aggressive enough that WP5 would not achieve the design life. Sulfidation resistance rises with chromium, and WP9 carries 8.0 to 10.0 percent against WP5's 4.0 to 6.0. WP9 also carries roughly double the molybdenum, so it gains high temperature strength as well as corrosion resistance. See our WP5 fittings page for the comparison.
No, and the similar names cause real confusion. WP9 is 9Cr-1Mo used mainly for sulfidation resistance in refining. WP91 is modified 9Cr-1Mo with vanadium, niobium and nitrogen additions, engineered for creep strength in supercritical power plant. They share a chromium level but not a purpose, a microstructure or a set of fabrication requirements.
ASTM A234 caps hardness at 217 HBW for WP9, WP5 and WPR. Harder material is more susceptible to environmental cracking in refinery service where sulphide or hydrogen is present, so the cap is a service safeguard. Heat treatment therefore has to meet the mechanical minima while staying below the hardness ceiling.
Request a Quote
Send your fitting type, size, schedule and class, plus the sulphur content and operating temperature, and we will confirm grade suitability, certification and lead time.