Stainless Steel, Duplex & Nickel Alloy Pipe Fittings
Buttweld fittings match the pipe schedule; forged socket-weld and threaded fittings are rated by class. Choose the family and grade, then the fitting type, radius and schedule or class. We supply ASME B16.9, B16.11 and MSS SP-43 fittings with EN 10204 3.1 certificates.
- ASME B16.9
- ASME B16.11
- MSS SP-43
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What are pipe fittings?
Pipe fittings change the direction, size or branching of a pipe run. Buttweld fittings (elbows, tees, reducers, caps, stub ends) are made to ASME B16.9 dimensions with material to ASTM A403 (stainless), A815 (duplex), B366 (nickel alloys) or A234 (carbon and Cr-Mo). Small-bore forged socket-weld and threaded fittings follow ASME B16.11 with material usually to ASTM A182.
How to order pipe fittings: checklist
- Fitting type and angle — e.g. 90° LR elbow, equal tee, concentric reducer
- Size and schedule (buttweld) or class (forged)
- Material grade with class — e.g. ASTM A403 WP316L-S
- Seamless or welded construction
- Dimensional standard — ASME B16.9, B16.11 or MSS SP-43
- Certificate — EN 10204 3.1 or 3.2
Fittings by Material Family and Grade
Every fitting page sits under its grade. Open it for the material standard, classes and the fitting types made in that grade.
Types of Pipe Fittings
Buttweld vs Socket Weld vs Threaded
The joint type is decided by line size, pressure and whether the line must be radiographed or dismantled.
| Buttweld | Socket weld | Threaded | |
|---|---|---|---|
| Standard | ASME B16.9 · MSS SP-43 | ASME B16.11 | ASME B16.11 · B1.20.1 (NPT) |
| Sizes | ½" – 48" | ⅛" – 4" (usually ≤ 2") | ⅛" – 4" |
| Rating | Matches pipe schedule | Class 3000 / 6000 / 9000 | Class 2000 / 3000 / 6000 |
| Joint | Full-penetration weld, can be radiographed | Fillet weld, 1.5 mm gap | No welding |
| Use | Process lines, high integrity | Small-bore, high pressure | Instrument, utility, where welding is not allowed |
Elbow Radius and Fitting Class
| Choice | Rule of thumb |
|---|---|
| LR elbow (1.5D) | Default for process piping |
| SR elbow (1.0D, ASME B16.9; formerly B16.28) | Only where space is tight; higher pressure drop |
| 3D / 5D bends | Pigging and slurry lines |
| Class 3000 socket weld | Pairs with Sch 80 pipe |
| Class 6000 socket weld | Pairs with Sch 160 pipe |
| A403 / A815 class S · W · WX · WU | Seamless · maker's welds RT · all welds RT · all welds UT |
How Fitting Standards Fit Together
Pipe Fittings Grades & Material Standards
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 | ASTM B366 WPNICMC · ASTM B564 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L | ASTM A403 WP904L · ASTM A182 F904L | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 | ASTM A403 WP304 · ASTM A182 F304 | General corrosion resistance, food, water and architectural work |
| SS 304L | ASTM A403 WP304L · ASTM A182 F304L | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S | ASTM A403 WP310S · ASTM A182 F310 | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L | ASTM A403 WP316L · ASTM A182 F316L | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 | ASTM A403 WP321 · ASTM A182 F321 | High-temperature service between 425 and 815 °C |
| SS 347 | ASTM A403 WP347 · ASTM A182 F347 | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 | ASTM A815 WPS31803 / WPS32205 · ASTM A182 F51 / F60 | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 | ASTM A815 WPS32750 · ASTM A182 F53 | Seawater and high-chloride service where strength also matters |
| Inconel 600 | ASTM B366 WPNCI · ASTM B564 | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 | ASTM B366 WPNCMC · ASTM B564 | Seawater, high strength and high temperature in one alloy |
| Inconel 718 | a specification not yet established · a specification not yet established | Very high strength at temperatures up to about 650 °C |
| Incoloy 800 / 800H / 800HT | ASTM B366 WPNIC · ASTM B564 | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 | ASTM B366 WPHC276 · ASTM B462 / B564 | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 | ASTM B366 WPHC22 · ASTM B462 / B564 | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 | ASTM B366 WPNC · ASTM B564 | Seawater, hydrofluoric acid and marine service |
| Super Duplex S32760 | ASTM A815 WPS32760 · ASTM A182 F55 | Seawater firewater, injection and offshore piping |
| ASTM A106 Gr B | ASTM A234 WPB · ASTM A105 | High-temperature process and steam piping in refineries and power plants |
| ASTM A333 Gr 6 | ASTM A420 WPL6 · ASTM A350 LF2 | Cold-climate and refrigerated piping down to −45 °C |
| ASTM A335 P11 | ASTM A234 WP11 · ASTM A182 F11 | Steam and hot-oil piping up to about 550 °C |
| ASTM A335 P22 | ASTM A234 WP22 · ASTM A182 F22 | High-pressure steam and hydrogen service up to about 580 °C |
Guides, tools & standards for pipe fittings
Pipe Fittings for export
FOB / CIF · Nhava Sheva (JNPT), MumbaiPipe Fittings — questions buyers ask
What is the difference between LR and SR elbows?
A long-radius elbow has a centreline radius of 1.5 × NPS; a short-radius elbow is 1.0 × NPS (now in ASME B16.9, formerly B16.28) and is used only where space is tight.
Which socket-weld class goes with Sch 80 pipe?
Class 3000. Class 6000 goes with Sch 160, and Class 9000 with XXS.
What do WP-S, WP-W, WX and WU mean?
They are classes in ASTM A403 and A815: S seamless; W welded with the maker's welds radiographed; WX all welds radiographed; WU all welds ultrasonically tested.
Why leave a gap in a socket weld?
A gap of about 1.5 mm (1/16") between pipe end and socket bottom stops the weld cracking as the joint expands and contracts.