At Solitaire Fittings, we manufacture and export ASTM A234 WP91 Alloy Buttweld Fittings made from 9Cr-1Mo-V (Grade 91) chromium-molybdenum steel. These fittings are built for the hottest, highest-pressure lines in modern power and process plants, where ordinary carbon steel or low-chrome alloys such as WP11 and WP22 would lose strength or creep over time.
We supply elbows, tees, reducers, caps and stub ends in seamless and welded construction, manufactured to ASTM A234 and dimensioned to ASME B16.9 and ASME B16.28, with full heat-treatment records and EN 10204 3.1 certificates.
Table of Contents
- ➤ What are ASTM A234 WP91 Alloy Buttweld Fittings?
- ➤ Key Features of WP91 Fittings
- ➤ Types of ASTM A234 WP91 Alloy Buttweld Fittings
- ➤ ASTM A234 WP91 Fittings Specifications
- ➤ ASTM A234 WP91 Chemical Composition
- ➤ ASTM A234 WP91 Mechanical Properties
- ➤ Heat Treatment and Welding of WP91 Fittings
- ➤ Applications of ASTM A234 WP91 Fittings
- ➤ Why Choose Solitaire Fittings for WP91 Fittings?
What are ASTM A234 WP91 Alloy Buttweld Fittings?
ASTM A234 WP91 Alloy Buttweld Fittings are wrought pipe fittings made from modified 9% chromium, 1% molybdenum steel with controlled additions of vanadium, niobium and nitrogen. This "creep-strength-enhanced ferritic" (CSEF) steel keeps far higher strength above 500°C than conventional Cr-Mo grades, which allows thinner walls and lighter piping for the same pressure.
- ASTM A234 – the specification for wrought carbon and alloy steel fittings for moderate and high-temperature service.
- WP91 – the 9Cr-1Mo-V grade. It is the fitting equivalent of ASTM A335 P91 pipe, ASTM A182 F91 forgings and ASTM A387 Grade 91 plate.
- Type 1 and Type 2 – recent editions of ASTM A234 split WP91 into Type 1 (standard chemistry) and Type 2 (tighter limits on residual elements). Tell us which type your specification calls for.
Key Features of WP91 Fittings
- High creep-rupture strength at 550–600°C, so wall thickness can be reduced compared with WP22.
- Good resistance to oxidation and steam-side scaling.
- Low thermal expansion and high thermal conductivity, which reduce thermal fatigue during start-ups and shutdowns.
- Matches the chemistry of P91 pipe, so the whole line can be welded and heat treated as one system.
- Available seamless up to 24" and welded in larger sizes.
Types of ASTM A234 WP91 Alloy Buttweld Fittings
We supply the full range of ASTM A234 WP91 Alloy Buttweld Fittings:
➤ WP91 Long and Short Radius Elbows
45°, 90° and 180° elbows in long radius (1.5D) and short radius (1D) for main steam and hot reheat lines. 3D and 5D bends can be supplied for low-pressure-drop layouts.
➤ WP91 Equal and Reducing Tees
Seamless and welded tees used to branch high-temperature headers and drains.
➤ WP91 Concentric and Eccentric Reducers
Reducers that join pipes of different bore while keeping a smooth flow path, made to the same wall-thickness schedule as the connecting P91 pipe.
➤ WP91 Caps and Stub Ends
Caps to close header ends and test points, and stub ends for lap-joint flange connections.
➤ WP91 Crosses and Special Fittings
Crosses, laterals and fittings made to customer drawings for boiler and HRSG manufacturers.
ASTM A234 WP91 Fittings Specifications
| Parameter | Details |
|---|---|
| Material Grade | ASTM A234 WP91 / ASME SA234 WP91 (Type 1 or Type 2) |
| Equivalent Grades | P91 pipe (A335), F91 forgings (A182), UNS K90901, 1.4903 (X10CrMoVNb9-1) |
| Dimensional Standards | ASME B16.9, ASME B16.28, MSS SP-75 |
| Size Range | 1/2" to 24" seamless; larger sizes welded |
| Wall Thickness | SCH 20 to SCH XXS, or to match pipe wall |
| Construction | Seamless (WP91) and welded (WP91-W) |
| Ends | Bevelled ends to ASME B16.25 |
| Certification | EN 10204 3.1 / 3.2, IBR on request |
ASTM A234 WP91 Chemical Composition
Typical limits for WP91 Type 1 per ASTM A234 (weight %):
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.08 – 0.12 |
| Manganese (Mn) | 0.30 – 0.60 |
| Phosphorus (P) | 0.020 max |
| Sulfur (S) | 0.010 max |
| Silicon (Si) | 0.20 – 0.50 |
| Chromium (Cr) | 8.00 – 9.50 |
| Molybdenum (Mo) | 0.85 – 1.05 |
| Nickel (Ni) | 0.40 max |
| Vanadium (V) | 0.18 – 0.25 |
| Niobium (Nb) | 0.06 – 0.10 |
| Nitrogen (N) | 0.030 – 0.070 |
| Aluminium (Al) | 0.02 max |
ASTM A234 WP91 Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 585 – 760 MPa (85 – 110 ksi) |
| Yield Strength (min) | 415 MPa (60 ksi) |
| Elongation (min) | 20% |
| Hardness (max) | 248 HB |
Heat Treatment and Welding of WP91 Fittings
The strength of ASTM A234 WP91 Alloy Buttweld Fittings depends on a tempered-martensite structure, so heat treatment and welding must be controlled closely:
➤ Normalizing and Tempering
Fittings are normalized at about 1040–1080°C and then tempered at about 730–800°C. Every heat-treatment cycle is recorded on charts that we supply with the test certificates.
➤ Welding and PWHT
Welding needs preheat (typically around 200°C), a matching 9Cr-1Mo-V filler such as ER90S-B9 or E9015-B9, and post-weld heat treatment. Field welds that skip these steps can lose much of the creep strength.
➤ Hardness and PMI Checks
We hardness-test and PMI-check fittings before dispatch to confirm the grade and heat treatment.
Applications of ASTM A234 WP91 Fittings
- Main steam and hot reheat piping in supercritical and ultra-supercritical power plants
- Heat recovery steam generators (HRSG) in combined-cycle plants
- Boiler headers, superheater and reheater links
- High-temperature hydrogen and hydrocracker service in refineries
- Petrochemical furnace outlet and transfer lines
Related Alloy Steel Fittings
- Alloy Steel Buttweld Fittings
- ASTM A234 WP22 Alloy Buttweld Fittings
- ASTM A234 WP11 Alloy Buttweld Fittings
- ASTM A234 WP9 Alloy Buttweld Fittings
- ASTM A234 WP5 Alloy Buttweld Pipe Fittings
- Alloy Steel Forged Fittings
- ASTM A234 WPB Carbon Steel Buttweld Fittings
Why Choose Solitaire Fittings for WP91 Fittings?
- Grade 91 experience: we supply WP91 fittings with full heat-treatment charts, hardness and PMI records.
- Complete range: elbows, tees, reducers, caps and stub ends in seamless and welded construction.
- Inspection ready: third-party inspection, IBR and project-specific testing on request.
- Export support: packing, marking and documentation for shipments worldwide.
If you need ASTM A234 WP91 Alloy Buttweld Fittings for a new plant or a shutdown, send us your size, schedule, quantity and specification. Our team will reply with a detailed quotation for ASTM A234 WP91 Alloy Buttweld Fittings that matches your piping class.
Frequently Asked Questions
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