Types of Pipe Fittings Explained: Elbows, Tees, Reducers & More
By Ragnar Metals & Tubes Engineering Team • May 25, 2026 • 8 min read
Pipe fittings are used to change direction, branch, reduce, or terminate a piping run. Selecting the wrong end-type or fitting class can cause leaks, premature failure, or failed inspections. This guide explains every category you will encounter when ordering.
Three End-Connection Types
Before selecting any fitting, you must match the end-connection type to your piping system:
1. Butt-Weld (BW) Fittings — ASME B16.9
The ends of the fitting are welded directly to the pipe using a circumferential weld. This creates the strongest and most leak-proof connection type, suitable for high-pressure and high-temperature service.
- Standard: ASME B16.9 (factory-made wrought BW fittings)
- Wall thickness: Matched to pipe schedule (SCH 10, 20, 40, 80, 160, XXS)
- Size range: ½" to 48" NPS (DN15 to DN1200)
- Use when: Pressure class is 150 lbs or higher; service is critical; permanent installation with full radiographic (RT) or ultrasonic (UT) weld inspection is required.
2. Socket-Weld (SW) Fittings — ASME B16.11
The pipe is inserted into a socket (recess) and a single fillet weld is made around the outside of the socket.
- Standard: ASME B16.11
- Pressure class: Class 3000, 6000, 9000
- Size range: 1/8”" to 4" NPS only
- Use when: Small-bore (≤2") high-pressure instrumentation and utility lines where full-bore butt-weld is impractical. Not for services with severe corrosion (crevice can form inside socket).
3. Threaded (THRD) Fittings — ASME B16.11
NPT (National Pipe Taper) threads on both fitting and pipe mate together. No welding required.
- Standard: ASME B16.11 (NPT per ASME B1.20.1)
- Pressure class: Class 2000, 3000, 6000
- Size range: 1/8”" to 4" NPS
- Use when: Temporary connections; low-pressure utility service; maintenance lines where frequent disassembly is needed. Not for hydrogen or highly toxic services.
Fitting Shapes — What Each Does
| Fitting | Function | Common Angles / Types |
|---|---|---|
| Elbow (LR & SR) | Changes pipe direction | 45°, 90°, 180° (Return); Long Radius (1.5D) or Short Radius (1D) |
| Equal Tee | Splits/joins flow at 90°; all three ends same size | Straight tee |
| Reducing Tee | Branch outlet smaller than run pipe | E.g., 4"×4"×2" |
| Concentric Reducer | Reduces pipe bore — centreline stays aligned | Used in horizontal lines |
| Eccentric Reducer | Reduces pipe bore — one side flat | Used in horizontal pump suction lines to prevent air pockets |
| Cap | Closes the end of a pipe run | Domed end per ASME B16.9 |
| Stub End | Welded to pipe; used with backing flange for lap-joint connections | Type A (long) and Type B (short) per MSS SP-43 |
| Cross | Four-way junction | Equal or reducing |
| Coupling / Half Coupling | Joins two pipes of same bore (SW/THD only) | Full and half |
SS 90° LR Elbow
Nickel Alloy Elbow
Long Radius vs Short Radius Elbows
This is one of the most common specification mistakes:
- Long Radius (LR) elbow — radius of curvature = 1.5 × nominal pipe diameter. Lower pressure drop, lower erosion. Specify LR unless space is constrained.
- Short Radius (SR) elbow — radius = 1.0 × nominal pipe diameter. Higher pressure drop, used only where space is critically limited (equipment skids, ship engine rooms).
Material Standards Quick Reference
| Material | ASTM Standard for BW Fittings |
|---|---|
| Stainless Steel 304/316L | ASTM A403 (WP304/WP316L) |
| Duplex Steel 2205 | ASTM A815 (WP2205) |
| Super Duplex 2507 | ASTM A815 (WP2507) |
| Hastelloy C-276 | ASTM B366 (WPHC276) |
| Inconel 625 | ASTM B366 (WPNCI) |
| Titanium Grade 2 | ASTM B363 (WPT2) |
| Copper | ASTM B75 / B88 |
Need Pipe Fittings for Your Project?
Ragnar Metals & Tubes manufactures and exports butt-weld, socket-weld, and threaded fittings in stainless steel, duplex, super duplex, Hastelloy, Inconel, Monel, Nickel, Titanium, Copper, and Brass. Sizes ½" to 48". MTC 3.1 included.
WhatsApp Send EnquiryRelated pages: SS Fittings • Duplex Fittings • Hastelloy Fittings
