Stainless Steel BSP Pipe Fittings

Which stainless steel BSP fitting?

Threaded stainless steel BSP fittings: female parts tapped Rp, male parts threaded R, from 1/4" to 4" unless stated.

• Change direction: stainless steel 90° female/female BSP elbow, stainless steel 45° BSP elbow (up to 2"), stainless steel 90° male/female BSP elbow.
• Branch off: stainless steel equal tee, stainless steel cross (up to 3").
• Extend: stainless steel female/female coupling (BSP socket), cast (up to 2") or machined; stainless steel half socket, shorter; stainless steel male/male nipple.
• Reduce (1/8" to 3"): stainless steel reducing coupling (reducing socket), female/female; stainless steel reducing nipple, male/male; stainless steel male/female reducing bush (male on the larger size).
• Close off: stainless steel female end cap or stainless steel male blanking plug.
• Flexible hose: stainless steel hose tail, male (up to 2"). The pressure rating of the assembly also depends on the hose and the hose clip.
• Lock: stainless steel BSP lock nut (backnut), to lock an assembly or a fitting passing through a wall or panel. It does not seal on its own.

Unions (three-piece fittings), pipe nipples and weld-end pipe nipples: see below.

What are stainless steel BSP fittings used for?

Plumbing, pipework and pressure systems with BSP threads: water and all fluids compatible with 316 stainless steel, with compatibility to be checked case by case. Drinking water: compliant with the 4MS requirements and with the French order of 25 June 2020, according to the technical data sheet for the series.

316 stainless steel: pressure and temperature

The PN rating applies from −20 to 40 °C; above that, the permissible pressure falls (values marked ≈ are read from the curve in the technical data sheet). PN 20 = 20 bar from −20 to 40 °C, about 16.5 bar at 100 °C.

• PN 20: investment cast (lost wax) fittings in CF8M (AISI 316) to ISO 4144, plus the machined coupling and the half socket in AISI 316.
• PN 50: pipe series in AISI 316 (ANSI B36.19 SCH 40).
• PN 40: machined unions, with no high-temperature values in the technical data sheet. For hot applications, contact us.

BSP threads (ISO 7-1) and sizes

ISO 7-1 pairs a parallel female Rp thread with a taper male R thread (BSPT): the joint seals on the threads. This BSP thread is compatible neither with NPT (a different thread form) nor with the parallel G thread of ISO 228-1, which seals with a flat gasket. The size in inches is a designation, not a measurable diameter. See our guide to plumbing threads.

Stainless steel unions: PN 20 or PN 40?

A union has three pieces (two ends and a nut). It can be taken apart; the seal is metal to metal, at the cone seat.

• PN 20 (cast CF8M union, 1/4" to 4", high-temperature values published): stainless steel female/female union PN 20, stainless steel male/female union PN 20.
• PN 40 (machined union, 316L ends and CF8M nut, 1/2" to 2", no high-temperature values): stainless steel female/female union PN 40, stainless steel male/female union PN 40, stainless steel male/male union PN 40.

Choose according to the pressure at the working temperature: a PN 20 union does not replace a PN 40.

Weld-end unions and pipe nipples

Plain butt weld (BW) end; Ø is the outside diameter of the weld end.

• One threaded end: stainless steel female/butt weld union PN 20 (1/4" to 2"), stainless steel female/butt weld union PN 40 (1/2" to 2"), stainless steel male/butt weld union PN 20 (3/8" to 2"), stainless steel male/butt weld union PN 40 (1/2" to 2").
• Weld ends on both sides, no thread: stainless steel butt weld union PN 20, stainless steel butt weld union PN 40.
• Pipe series in AISI 316, ANSI B36.19 SCH 40, PN 50: stainless steel male/butt weld adaptor (1/4" to 2"); stainless steel male/butt weld pipe nipple (1/4" to 1") and stainless steel male/male pipe nipple (1/4" to 4"), both in 100 or 150 mm lengths.

Welding by a qualified welder, with the process and filler metal chosen for the installation; take the union apart before welding to protect the seat. The range has no weld-end elbows, tees or reducers.

Threaded, press-fit or welded?

The range covers BSP threaded fittings in inch sizes and the weld-end fittings above: a threaded joint can be taken apart; a weld is permanent, but a weld-end union still lets you dismantle the assembly. The range does not include press-fit fittings, which need tube and tools specific to their system, compression fittings (olive, cutting ring), plain tube in mm sizes or hygienic fittings (clamp, DIN, SMS).

Stainless steel, brass or malleable iron?

The same functions are available as brass fittings and black malleable iron fittings: brass nipples and sockets, black malleable iron nipples and sockets, black malleable iron unions. All materials: elbows, tees, caps and plugs.

The mating part must have the complementary R or Rp thread to ISO 7-1. Note that, with few exceptions, our flat-seal and conical-seat brass fittings are threaded to ISO 228-1 (BSPP, parallel), not R male: check the product page. On a water system, stainless steel forms a galvanic couple with galvanized steel or cast iron: allow for this.

Frequently asked questions

What is the pressure rating at 100 °C?

≈ 16.5 bar for PN 20, ≈ 40 bar for PN 50; PN 40 unions: no published value, please consult us.

BSP or NPT thread?

BSP to ISO 7-1 (Rp parallel, R taper), not compatible with NPT.

316 or 304 stainless steel?

The whole range is 316: CF8M for the cast parts, 316L (low carbon) for the ends of the PN 40 unions. Unlike 304, 316 contains molybdenum and has better resistance to chlorides.

Are they suitable for drinking water?

Yes: compliant with the 4MS requirements and with the French order of 25 June 2020, according to the technical data sheet for the series.

How do I seal a stainless steel thread without galling?

On the threads, with PTFE or jointing compound suited to the fluid and the temperature. With stainless steel on stainless steel, the thread can gall: screw in gradually, without forcing, using an open-ended or adjustable spanner on the flats, or a strap wrench on a part without flats; never use pipe grips or pliers, which mark stainless steel. Method: how to screw fittings and pipes together.