Stainless steel union, female/female 316, PN 20, BSP threaded
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| Product Type | Delivery Method | Preparation Time | Transport Time | Delivery Time |
|---|---|---|---|---|
| All Parts | Pickup Point | 0 to 3 days | 3 to 6 days | 3 to 9 days |
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| Tubes > 90cm | Home Delivery | 0 to 3 days | 3 to 5 days | 3 to 8 days |
| Tubes < 200cm | Home Delivery | 0 to 3 days | 3 to 5 days | 3 to 8 days |
| Tubes > 200cm | Home Delivery | 0 to 6 days | 6 to 10 days | 6 to 16 days |
| Assembled Products | Home Delivery & Pickup Point | 0 to 5 days | (see methods) | 3 to 11 days |
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Stainless steel union, female/female 316, PN 20, BSP threaded
Stainless steel union, female/female 316, PN 20, tapped BSP (Rp to ISO 7-1) at both ends, from 1/4" to 4" (DN8 to DN100). This 3-piece conical (taper) seat union provides a point of disconnection on threaded pipework. PN 20 up to 40 °C, drinking water compliant, for all fluids compatible with stainless steel.
Description of the stainless steel union 316 PN 20 with conical seat
This 3-piece stainless steel union consists of two ends and a nut. At the conical seat, the seal is metal to metal between the two ends. Undoing the nut opens the joint without unscrewing the connected pipework.
This union is investment cast (lost wax) in CF8M (AISI 316) stainless steel, and designed, manufactured and inspected to ISO 4144. The ends have flats (dimension B on the drawing) and the nut has 8 or 10 sides depending on size.
Does your working pressure exceed the PN 20 limit at your temperature? See the stainless steel union 316L PN 40, from 1/2" to 2". Its permissible pressure falls as temperature rises and we have no figure for it: for hot applications, contact us before choosing.
Stainless steel union PN 20: 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: two ends and a nut |
| Seal at the seat | Metal to metal |
| Shape | Ends with flats, nut with 8 or 10 sides depending on size |
| Thread | Rp tapped (parallel) to ISO 7-1 (BSP, R series). Mates with an R male thread (taper). Not compatible with NPT |
| Connection | Female/female |
| 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 | 11 sizes, from 1/4" to 4" |
| 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
This union is used on drinking water systems and on circuits carrying fluids compatible with 316 stainless steel, wherever a component must stay removable. Check fluid compatibility and the permissible pressure at the working temperature.
- Thread sealing: an Rp/R joint seals on the threads, using PTFE or jointing compound suited to the fluid and the working temperature.
- Conical seat: it seals metal to metal. Keep it clean on assembly and at every reassembly.
- Galling: with stainless steel on stainless steel, the thread can gall. Screw in gradually, without forcing.
- Tightening: hold the end with an open-ended or adjustable spanner on its flats and tighten the nut the same way, not with pipe grips or pliers, which mark stainless steel.
- Dissimilar metals: on a water system, stainless steel forms a galvanic couple with galvanized steel or cast iron. Allow for this when choosing the connected components.
Technical drawing
Dimensions (mm)
Dimensions in millimetres, PN in bar, weight in kilograms.
| Rp size | French size | A | B | ØC | L1 | L2 | Nut sides | PN (bar) | Weight (kg) |
|---|---|---|---|---|---|---|---|---|---|
| 1/4" | 8x13 | 27 | 17 | 14 | 34.5 | 13.5 | 8 | 20 | 0.065 |
| 3/8" | 12x17 | 32 | 20.5 | 17 | 37.5 | 15.5 | 8 | 20 | 0.090 |
| 1/2" | 15x21 | 37 | 26 | 21 | 42 | 16.5 | 8 | 20 | 0.139 |
| 3/4" | 20x27 | 46 | 31 | 27 | 43.5 | 17.5 | 8 | 20 | 0.199 |
| 1" | 26x34 | 52 | 38 | 33.5 | 50.5 | 20.5 | 10 | 20 | 0.262 |
| 1"1/4 | 33x42 | 65 | 48 | 42.5 | 54.5 | 22.5 | 10 | 20 | 0.442 |
| 1"1/2 | 40x49 | 70 | 54 | 49 | 58.5 | 24.5 | 10 | 20 | 0.517 |
| 2" | 50x60 | 84 | 66 | 59.5 | 67 | 27.5 | 10 | 20 | 0.821 |
| 2"1/2 | 66x76 | 108 | 82 | 77.5 | 74.5 | 29 | 10 | 20 | 1.373 |
| 3" | 80x90 | 116 | 95 | 90 | 86 | 31.5 | 10 | 20 | 1.578 |
| 4" | 102x114 | 142.5 | 120 | 114.5 | 111 | 34.5 | 10 | 20 | 2.565 |
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).
| French size | 8x13 | 12x17 | 15x21 | 20x27 | 26x34 | 33x42 | 40x49 | 50x60 | 66x76 | 80x90 | 102x114 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Inches | 1/4" | 3/8" | 1/2" | 3/4" | 1" | 1"1/4 | 1"1/2 | 2" | 2"1/2 | 3" | 4" |
| DN | DN8 | DN10 | DN15 | DN20 | DN25 | DN32 | DN40 | DN50 | DN65 | DN80 | DN100 |
| OD (French size) | 13 mm | 17 mm | 21 mm | 27 mm | 34 mm | 42 mm | 49 mm | 60 mm | 76 mm | 90 mm | 114 mm |
Stainless steel union PN 20: frequently asked questions
PN 20 or PN 40?
The choice depends on the working pressure at the working temperature. This PN 20 union covers 1/4" to 4", with published high-temperature values. The PN 40 union covers 1/2" to 2", with 316L ends and a CF8M nut, and has no published high-temperature values. A PN 20 union is not suitable if your installation requires PN 40.
What is the pressure rating at 100 °C?
≈ 16.5 bar, against 20 bar from −20 to 40 °C.
BSP or NPT thread?
BSP to ISO 7-1: Rp parallel tapped thread, for use with an R taper male thread. This union is not compatible with NPT.
316 or 304 stainless steel?
This union is 316 (CF8M). Unlike 304, 316 contains molybdenum and has better resistance to chlorides.
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 union 316L PN 40, stainless steel 90° female/female elbow, stainless steel female/female coupling.
Other materials: brass fittings, black malleable iron unions.
Useful guides:
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