Threaded fittings, also called screwed fittings, join small-bore pipe without welding: the pipe end is threaded and screwed into a female-threaded forged fitting. Made to ASME B16.11 in Class 2000, 3000 and 6000 with NPT threads to ASME B1.20.1, or BSPT / BSPP threads to BS 21 / ISO 7-1, they are used where hot work is restricted, on galvanised and utility piping, on instrument and gauge connections, and wherever joints must be taken apart for maintenance.
Raaj Fittings forges and machines threaded elbows, street elbows, tees, crosses, couplings, caps, plugs, bushings and nipples in-house at our two plants in India, from ⅛" to 4", in carbon, alloy and stainless steel, duplex and nickel alloys, for stockists, OEMs and contractors in the Middle East, Europe and the Americas.
| Thread | Standard | Form | Typical market |
|---|---|---|---|
| NPT | ASME B1.20.1 | Taper 1 in 16, 60° thread angle | Americas, Middle East, most oil and gas |
| BSPT (R / Rc) | BS 21 / ISO 7-1 | Taper 1 in 16, 55° thread angle | UK, Europe, Asia, Australia |
| BSPP (G) | ISO 228-1 / BS 21 | Parallel, 55°; seals on a washer or O-ring | Hydraulic and instrument equipment |
| Class | Matching pipe | Typical use |
|---|---|---|
| 2000 | SCH 80 / XS | Utility, water and air lines |
| 3000 | SCH 160 | General process, instrument and drain connections |
| 6000 | XXS | High-pressure hydraulic, injection and steam service |
Threading removes part of the pipe wall, so threaded pipe is normally at least SCH 80 and the fitting class is chosen one step lower than the equivalent socket weld class for the same pipe.
Threads are checked with gauges against ASME B1.20.1 or BS 21 / ISO 7-1, and fittings are inspected dimensionally against ASME B16.11. Each fitting is marked with the manufacturer's mark, material, class and size, plus the heat number, and supplied with EN 10204 3.1 certificates; EN 10204 3.2 certification and third-party inspection by the buyer's nominated agency are available on request.
NPT (ASME B1.20.1) has a 60° thread angle and is used mainly in the Americas and oil and gas. BSP (BS 21 / ISO 7-1) has a 55° angle and different pitches in most sizes. They are not interchangeable, so order the thread your equipment uses.
Class 3000 threaded fittings match SCH 160 pipe. Class 2000 matches SCH 80 and Class 6000 matches XXS.
Taper threads seal by wedging, but a sealant or PTFE tape is used to fill the small spiral leak path. If the joint is to be seal welded, no sealant should be used on the threads.
Usually with limits. Codes such as ASME B31.3 restrict threaded joints in severe cyclic, toxic or flammable service and above certain sizes. Check your piping specification; socket weld fittings are the usual alternative.
From ⅛" to 4" NPS to ASME B16.11, in Class 2000, 3000 and 6000, with NPT, BSPT or BSPP threads.