IBR Approved · Stainless Steel
ASTM A403 WP321 Buttweld Pipe Fittings
Titanium-stabilised 321 (18Cr-10Ni-Ti) austenitic stainless steel — for high-temperature service to 815°C without sensitization. Exhaust systems, expansion joints and heat-exchanger headers. Elbows, tees, reducers and caps to ASME B16.9 / B16.28, IBR approved with Form IV (Part D) (formerly Form III-C), EN 10204 3.1 / 3.2 traceable.
Where WP321 Is Used
- ✓ High-temperature exhaust, ducting and expansion lines
- ✓ Refinery lines exposed to polythionic acid during shutdowns
- ✓ Process piping held at temperatures where unstabilised grades sensitise
WP321 Compared With Related Grades
| Grade | Chemistry | Key difference |
|---|---|---|
| A403 WP304L | Low carbon | Relies on low carbon, not stabilisation |
| A403 WP321 | 18Cr-10Ni-Ti | Titanium-stabilised for sustained high-temperature service |
| A403 WP347 | 18Cr-10Ni-Nb | Niobium-stabilised alternative |
| A403 WP316L | +Mo | Better chloride resistance at lower temperatures |
How to Specify WP321 Fittings on a Purchase Order
A complete order line avoids clarification rounds. Example:
Elbow 90° LR, 6" SCH 10S, ASTM A403 WP321-S, ASME B16.9, EN 10204 3.1
- ✓ State the class: WP-S, WP-W or WP-WX
- ✓ Add an intergranular corrosion test (ASTM A262) if required
- ✓ State the service temperature so the stabilised grade can be confirmed
Grade Overview
ASTM / ASME A403 WP321 is a titanium-stabilised austenitic stainless steel. Titanium is added at a minimum of five times the carbon content to tie up carbon as stable titanium carbides, preventing chromium-carbide precipitation (sensitization) during prolonged exposure in the 425–815°C range. This makes 321 the standard choice for high-temperature components that cannot be solution annealed after welding.
321 fittings are supplied IBR approved with Form IV (Part D) for boiler and steam service. The EN counterpart is 1.4541 (X6CrNiTi18-10).
✓ No PWHT — welded with ER347 filler
As an austenitic stainless steel, 321 does not require post-weld heat treatment. It is welded with ER347 (niobium-stabilised) filler, not ER321, because titanium is lost across the welding arc — the niobium-stabilised filler provides equivalent weld-metal stabilisation. ASME P-No. 8, Group 1.
Chemical Composition — WP321 / 1.4541
| Standard | C | Cr | Ni | Ti | Mn | Si |
|---|---|---|---|---|---|---|
| ASTM A403 WP321 | ≤0.08 | 17.0–19.0 | 9.0–12.0 | 5×C – 0.70 | ≤2.0 | ≤1.0 |
| EN 1.4541 | ≤0.08 | 17.0–19.0 | 9.0–12.0 | 5×C – 0.70 | ≤2.0 | ≤1.0 |
Mechanical Properties — WP321
| Property | Requirement |
|---|---|
| Tensile Strength (min) | 515 MPa (75 ksi) |
| Yield Strength (min) | 205 MPa (30 ksi) |
| Elongation (min) | ≥ 35% |
| Heat Treatment | Solution annealed |
Equivalent Grades
| Product Form | Specification |
|---|---|
| Buttweld fittings | ASTM / ASME A403 WP321 · EN 1.4541 · UNS S32100 |
| Seamless pipe | ASTM A312 TP321 |
| Forgings / flanges | ASTM A182 F321 |
| Plate | ASTM A240 321 |
EN 10253 equivalent: see 321 pipe fittings on arshyapipefittings.com, and the European grade EN 1.4541 (X6CrNiTi18-10).
Fitting Types Available in 321
- Elbows — 45° / 90° / 180°, LR & SR
- Tees — equal & reducing
- Reducers — concentric & eccentric
- Caps & Stub Ends — closures & lap joints
Related grades: 304L · 316L · Stub ends · IBR Form IV (Part D) guide · IBR grades list
Testing & Inspection — 321
- Chemical analysis of each heat, confirming titanium at the stabilising level ASTM A403 requires relative to carbon and nitrogen.
- Tensile test to ASTM A403 (515 MPa min. tensile, 205 MPa min. yield) after solution annealing.
- Intergranular corrosion test (ASTM A262) available on request.
- Positive material identification (PMI), and pickling & passivation.
- Dimensional and visual inspection to ASME B16.9; weld RT/UT for welded classes.
Dimensions & Size Range — ASME B16.9
321 fittings are made to ASME B16.9 (long-radius) and ASME B16.28 (short-radius elbows) dimensions, from 1/2" to 48" NB and above. Wall thickness matches the connecting pipe schedule. Centre-to-end dimensions for the most-ordered sizes:
| NPS | Outside diameter (mm) | 90° LR elbow “A” (mm) | 45° LR elbow “B” (mm) | Equal tee “C” (mm) |
|---|---|---|---|---|
| 1/2" | 21.3 | 38 | 16 | 25 |
| 1" | 33.4 | 38 | 22 | 38 |
| 2" | 60.3 | 76 | 35 | 64 |
| 3" | 88.9 | 114 | 51 | 86 |
| 4" | 114.3 | 152 | 64 | 105 |
| 6" | 168.3 | 229 | 95 | 143 |
| 8" | 219.1 | 305 | 127 | 178 |
| 10" | 273.1 | 381 | 159 | 216 |
| 12" | 323.9 | 457 | 190 | 254 |
| 16" | 406.4 | 610 | 254 | 305 |
| 20" | 508.0 | 762 | 318 | 381 |
| 24" | 610.0 | 914 | 381 | 432 |
Long-radius elbows have a centre-line radius of 1.5 × NPS; short-radius (ASME B16.28) 1.0 × NPS. Full tables to NPS 48, reducing tees, reducers and caps are available with every quotation. For EN 10253 dimensions see arshyapipefittings.com.
Export Documentation & Packing
We ship 321 fittings to projects outside India with the documents EPC contractors and inspection agencies expect:
- Mill test certificate — EN 10204 3.1 as standard; 3.2 with third-party witness
- Third-party inspection — Bureau Veritas, TÜV, Lloyd’s Register, SGS, DNV or the client’s own inspector
- IBR Form IV (Part D) — for boiler piping on Indian Boiler Regulations projects
- Traceability — every fitting marked with grade, size, schedule and heat number, matching the certificate
- Packing — seaworthy wooden cases or pallets, bevel ends protected with end caps
- Shipping documents — commercial invoice, packing list and certificate of origin; FOB, CFR or CIF terms
Send your BOQ through the RFQ form (Excel or PDF attachments accepted) or on WhatsApp — quotations are usually issued within 24 hours.
321 Fittings — Frequently Asked Questions
What is the difference between 321 and 347?
Both are stabilised grades that resist sensitisation at elevated temperature: 321 with titanium, 347 with niobium. Titanium does not transfer well across the welding arc, which is why 321 is normally welded with ER347 (niobium-stabilised) filler.
Should I specify 321 or 321H?
321H has a controlled higher carbon content for better creep strength at high temperature; 321 is the usual choice for general elevated-temperature and corrosive service. State which one your design code calls for.
Why is 321 used in refinery units?
Because stabilised grades resist polythionic acid stress-corrosion cracking during shutdowns, which attacks sensitised unstabilised stainless. See polythionic acid SCC explained.