Stainless steel union, male/butt weld 316, PN 20, BSP threaded
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Stainless steel union, male/butt weld 316, PN 20, BSP threaded
Stainless steel union, male/butt weld 316, PN 20: one end is BSP threaded (R taper to ISO 7-1) and screws into an Rp tapped thread; the other, plain, is welded (BW) to the pipe, from 3/8" to 2" (DN10 to DN50). The nut opens the joint without unscrewing the component or cutting the pipe. Drinking water compliant, it is rated PN 20 up to 40 °C for any fluid compatible with stainless steel.
Description of the stainless steel union, male/butt weld 316 PN 20
This stainless steel union has 3 pieces: a male end with flats, a plain weld end and a nut. The seal is metal to metal, at the conical seat between the ends. To open it, undo the nut: the welded pipe and the screwed component stay in place.
It is investment cast (lost wax) in CF8M (AISI 316) stainless steel, and designed, manufactured and inspected to ISO 4144. On the BW side, for butt welding, dimension Ø ranges from 17.2 to 60.3 mm.
Need more than PN 20 at your temperature? The stainless steel union, male/butt weld 316L PN 40 covers 1/2" to 2", with no high-temperature figures: for hot applications, contact us. If the joint does not need to open, see the stainless steel male/butt weld adaptor 316, which has no nut.
Stainless steel male/butt weld union: technical specifications
| Material | CF8M (AISI 316) stainless steel |
| Manufacture | Investment casting (lost wax) |
| Standard | Designed, manufactured and inspected to ISO 4144 |
| Type | Conical (taper) seat union, 3-piece: a male end, a weld end and a nut |
| Seal at the seat | Metal to metal |
| Shape | Male end with flats, plain weld end, nut with flats |
| Thread | R taper to ISO 7-1 (BSP, R series). Mates with an Rp female thread (parallel). Not compatible with NPT |
| Weld end | Plain BW end, for butt welding, Ø 17.2 to 60.3 mm |
| Connection | Male/butt weld |
| Nominal pressure | PN 20: 20 bar from −20 to 40 °C, lower above that |
| Temperature | −20/+220 °C, permissible pressure reduced above 40 °C |
| Fluids | All fluids compatible with stainless steel |
| Sizes | 7 sizes, from 3/8" to 2" |
| Compliance | 4MS; drinking water: French order of 25 June 2020 |
Pressure and temperature
PN 20 applies from −20 to 40 °C. Above that, the permissible pressure falls. Values marked ≈ are read from the pressure/temperature curve in the technical data sheet.
| Temperature (°C) | Max. pressure (bar) |
|---|---|
| −20 → 40 | 20 |
| 100 | ≈ 16.5 |
| 150 | ≈ 15 |
| 220 | ≈ 13.5 |
Certification and compliance
According to the technical data sheet for the series:
- 4MS: compliant with the 4MS requirements, the harmonized European rules for materials and products in contact with drinking water.
- Drinking water: compliant with the French order (arrêté) of 25 June 2020 on metallic materials and products in contact with water intended for human consumption.
Uses and installation advice
It is used on drinking water systems and on circuits carrying fluids compatible with 316 stainless steel. Check fluid compatibility and the permissible pressure in service.
- BW side: have the weld made by a qualified welder. The welding process and filler metal depend on the installation. Separate the ends before welding to protect the conical seat.
- Thread sealing: an Rp/R joint seals on the threads, using PTFE or jointing compound suited to the fluid and the working temperature.
- Galling: with stainless steel on stainless steel, the thread can gall. Screw in gradually, without forcing.
- Tightening: screw in and hold the male end with an open-ended or adjustable spanner on its flats, then tighten the nut the same way. Avoid pipe grips and pliers, which mark stainless steel.
- Dissimilar metals: on a water system, stainless steel forms a galvanic couple with galvanized steel or cast iron.
Technical drawing
Dimensions (mm)
A: overall length. Ø: outside diameter of the weld end. B: outside dimension of the nut. R: male thread, R size column. Dimensions in millimetres, PN in bar, weight in kilograms.
| R size | French size | Ø | A | B | PN (bar) | Weight (kg) |
|---|---|---|---|---|---|---|
| 3/8" | 12x17 | 17.2 | 45 | 37 | 20 | 0.113 |
| 1/2" | 15x21 | 21.3 | 52 | 40 | 20 | 0.160 |
| 3/4" | 20x27 | 26.9 | 58 | 49.5 | 20 | 0.230 |
| 1" | 26x34 | 33.7 | 66 | 56 | 20 | 0.325 |
| 1"1/4 | 33x42 | 42.4 | 72.5 | 67 | 20 | 0.459 |
| 1"1/2 | 40x49 | 48.3 | 77.5 | 73 | 20 | 0.549 |
| 2" | 50x60 | 60.3 | 91 | 90 | 20 | 0.898 |
Size conversion
Conversion between the French size designation, inches, DN and the outside diameter stated in the designation (a rounded value, not a pipe dimension). For welding, the dimension that matters is Ø.
| French size | 12x17 | 15x21 | 20x27 | 26x34 | 33x42 | 40x49 | 50x60 |
|---|---|---|---|---|---|---|---|
| Inches | 3/8" | 1/2" | 3/4" | 1" | 1"1/4 | 1"1/2 | 2" |
| DN | DN10 | DN15 | DN20 | DN25 | DN32 | DN40 | DN50 |
| OD (French size) | 17 mm | 21 mm | 27 mm | 34 mm | 42 mm | 49 mm | 60 mm |
Stainless steel male/butt weld union: frequently asked questions
The component I am connecting to is male: which union should I choose?
This one screws into an Rp tapped thread. On a male thread, choose the stainless steel female/butt weld union PN 20.
What is the pressure rating at high temperature?
≈ 16.5 bar at 100 °C and ≈ 13.5 bar at 220 °C, against 20 bar from −20 to 40 °C.
BSP or NPT thread?
BSP to ISO 7-1: R taper thread, for use with an Rp parallel female thread. This union is not compatible with NPT.
The appearance of the part may vary depending on the batch in stock. Contact us for confirmation.
See also
Full range: all stainless steel BSP fittings
Other stainless steel fittings: stainless steel butt weld union PN 20 for welding at both ends, stainless steel male/female union PN 20 for screwing at both ends.
Other materials: brass fittings, black malleable iron unions.
Useful guides:
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