Steel pipe nipples are among the simplest yet most essential components in piping systems. A nipple is a short length of pipe, typically threaded on both ends, used to connect fittings or extend pipe runs. Despite their simplicity, nipples come in various types, sizes, materials, and standards.
What Is a Pipe Nipple?
A pipe nipple is a short piece of straight pipe with threads on both ends. Lengths range from 12mm (close nipple) to several meters. Nipples serve as connectors, extensions, or adapters across oil and gas, chemical processing, fire protection, plumbing, and HVAC.
Types of Steel Pipe Nipples
1. Close Nipple
No unthreaded portion between threads. Shortest possible nipple. Used when two fittings must be connected with minimal space. Cannot be gripped with a pipe wrench on the threaded portion.
2. Standard (Regular) Nipple
Plain section between threaded ends. Available 50mm to 300mm+. Most common type for general piping connections, fire sprinkler drops, and instrument connections.
3. Swage Nipple
Connects two pipes of different diameters. Available as concentric (shared centerline) or eccentric (flat side for maintaining elevation). Used for pipe size transitions, pump connections, and tank nozzle connections.
4. Weld Nipple
One or both ends prepared for butt welding. Provides smooth, leak-free connection without threaded leak paths. Used in high-pressure and critical service applications.
5. Hex Nipple
Hexagonal section in the middle for wrench tightening. Can be tightened without access to both ends. Used for valve connections and instrument manifolds.
Thread Standards
NPT (National Pipe Taper): Most common in North America. 60° V-thread, 1 in 16 taper. Requires thread sealant (PTFE tape, pipe dope). Defined by ASME B1.20.1.
BSPT (British Standard Pipe Taper): Common in Europe, Asia, Middle East. 55° Whitworth form, same taper as NPT. NOT interchangeable with NPT. Defined by ISO 7-1.
BSPP (British Standard Pipe Parallel): Non-tapered. Seals using bonded seal washer or O-ring. More reliable sealing than tapered threads. Defined by ISO 228-1.
Materials
| Material | Standard | Applications |
|---|---|---|
| Carbon Steel | ASTM A733, A120 | General service, fire protection, plumbing |
| Stainless Steel 304 | ASTM A312 | Chemical, food processing, marine |
| Stainless Steel 316 | ASTM A312 | Marine, chemical, pharmaceutical |
| Alloy Steel (Cr-Mo) | ASTM A182 | High-temperature, high-pressure (power plants) |
| Brass | ASTM B43 | Plumbing, gas, instrumentation |
Pressure Ratings (Carbon Steel NPT)
| Size (inches) | Max Pressure @ Ambient (PSI) | Max Pressure @ 450°F (PSI) |
|---|---|---|
| 1/8 – 3/4 | 1,000 | 800 |
| 1 – 2 | 800 | 650 |
| 2 1/2 – 4 | 500 | 400 |
| 6 – 8 | 300 | 250 |
Standards and Specifications
- ASME B1.20.1: Pipe threads, general purpose (inch) — NPT standard
- ASME B16.11: Forged fittings, socket-welding and threaded
- ASTM A733: Welded and seamless carbon steel and alloy steel threaded pipe nipples
- MSS SP-95: Swage(d) nipples and bull plugs
Installation Best Practices
- Use appropriate thread sealant for NPT connections
- Apply sealant to male threads only
- Hand-tighten first, then wrench for final make-up (2-3 turns past hand-tight)
- Do not over-tighten
- Never reuse pipe dope from a disassembled connection
Summary
Steel pipe nipples are simple components with critical importance. From close nipples for tight spaces to swage nipples for size transitions, each type serves a specific purpose in piping design and installation.
CoreMetal Steel supplies carbon steel and stainless steel pipe nipples in all standard sizes and configurations, manufactured to ASME and ASTM standards.