A buttweld fitting is a weldable pipe fitting that allows for change of direction of flow, to branch off, reduce pipe size or attach auxiliary equipment. Forged Steel buttweld fittings are manufactured in accordance with ANSI / ASME B16.9.
Butt weld fittings are available as elbows, tees, caps, reduces and out lets (olets). These fittings are the most common type of welded pipe fitting and are specified by nominal pipe size and pipe schedule. Buttweld fittings use seamless or welded pipe as the starting material and are forged (through multiple process) to get he shape of elbows, tees and reducers etc. Just as the pipe is sold from Schedule 10 to Schedule 160, butt weld pipe fittings are sold the same way. Welded butt weld fittings are more common in stainless steel due to cost advantage. Sch 10 fittings are also more common in stainless steel butt weld fitting.
Common material for butt weld fittings are A234 WPB (A & C also available), High Yield Carbon Steel, Stainless Steel 304 and 316 and Nickel Alloys.
Buttweld pipe fittings comprises of long radius elbow, concentric reducer, eccentric reducers and Tees.They are an important part of industrial piping system to change direction, branch off or to mechanically join equipment to the system. Buttweld fittings are sold in nominal pipe sizes with specified pipe schedule. BW fitting’s dimensions and tolerances are defined as per ASME standard B16.9.
Butt Weld fittings are also called Welded Pipe fittings. These welded fittings in carbon steel and stainless steel offer many advantages compared to threaded and socketweld fittings. The later are only available up to 4-inch nominal size whereas butt weld fittings are available in sizes from ½” to 72”. Some of the benefits of Buttweld fittings are;
Welded pipe fittings in carbon steel and stainless steel are the joining components that make possible the assembly of valves, pipes and equipment onto the piping system. Welded fittings compliment pipe flanges in any piping system and allows;
Change direction of flow in a piping system
Connect or joint pipes and equipment
Provide branches, access and takeoffs for auxiliary equipment
A common example using welded pipe fitting is a pipe reduced by concentric reducer, welded to a weld neck flange and connected to an equipment. Figure below represent complete collection of butt welded pipe fitting
Common Materials for Welded Pipe Fittings
Carbon Steel Welded Fitting:
A234 WPB is the most common material used for carbon steel butt welded fittings.
ASTM A234 WPB is the Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service.
Specifications
ASTM: A234 WPB
ASME: B16.9, B.11
NACE: MRO175
MSS: SP-83, SP-95
Chemical Composition%
| Grade | C | Mn | P | S | Si | Cr | Mo | Ni | Cu | Others |
| – | – | – | max | max | – | – | – | – | – | – |
| WPB | 0.3 | 0.29-1.06 | 0.05 | 0.058 | 0.1 | 0.4 | 0.15 | 0.4 | 0.4 | V 0.08 |
| (1,2,3,4,5) | max | – | – | – | min | max | max | max | max | max |
- Fittings made from bar or plate may have 0.35 max carbon.
- Fittings made from forgings may have 0.35 max Carbon and 0.35 max Silicon with no min.
- For each reduction of 0.01% below the specified Carbon maximum, an increase of 0.06% Manganese above the specified maximum will be permitted, up to a maximum of 1.35%.
- The sum of Copper, Nickel, Niobium, and Molybdenum shall not exceed 1.00%.
- The sum of Niobium and Molybdenum shall not exceed 0.32%.
Stainless Steel Butt Weld Fittings:
Stainless buttweld fittings are available in 316 and 304 grades.
304/304L (UNS S30400/S30403)
Chemical Composition%
| C | Cr | Mn | Ni | P | S | Si |
| MAX | – | MAX | – | MAX | MAX | MAX |
| 0.035 | 18.0- 20.0 | 2.00 | 8.0-13.0 | 0.045 | 0.030 | 1.00 |
Tensile Requirements
Tensile Strength: (KSI) = 60
Yield Strength: (KSI) = 35
(KSI converts to MPA {Megapascals} by multiplying by 6.895)
316/316L (UNS S31600/S31603)
Chemical Composition%
| C | Cr | Mn | Mo | Ni | P | S | Si |
| MAX | – | MAX | – | Max | MAX | MAX | |
| 0.035 | 16.0- 18.0 | 2.00 | 2.0-3.0 | 10.0-14.0 | 0.045 | 0.030 | 1.00 |
Tensile Requirements
Tensile Strength: (KSI) = 70
Yield Strength: (KSI) = 25
(KSI converts to MPA {Megapascals} by multiplying by 6.895)
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Butt weld (BW) fittings are defined in the ASME B16.9. They are welded at their ends to pipe end, with the same thickness as pipes. The end of butt weld fittings shall be beveled.