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Socket Weld Flanges

A socket weld flange has a socket into which the pipe is inserted. The tube is attached to the outside of the flange he hub by a fillet weld. A significant drawback of this type of flange is that the weld is difficult to verify and is not considered a high integrity joint. Socket weld flanges are therefore only suitable for low to medium grades (≤ ASME 600). Socket weld flanges are often flat or raised because they have poor integrity and are not suitable for high pressure applications.

The Socket Weld Flange is designed for small nominal pipe sizes (≤ 4 inches, ≤ 10 cm) and is common on ½ to 2 inch pipe sizes (1.3 to 5 cm pipe sizes). The mechanical strength of socket weld flanges is similar to slip-on flanges, but slip-on flanges can use two welds.

The ASME B31.3 standard states that there should be approximately 1⁄16 inch (1.5 mm) clearance between the socket and the end of the pipe. This gap allows thermal expansion from the weld and reduces the chance of weld cracking. In practice, this means that the tube must be fully inserted into the flange and then withdrawn the desired amount (1/16 inch, 1.5 mm). This gap is highlighted in red in the image above.

The advantage of the socket weld flange is its simple construction. 2 inches (5 cm) or less for non-critical applications. Non-hazardous systems; they are not suitable for erosive or highly corrosive systems.

Non-Destructive Testing (NDT) Techniques
A socket weld flange has only one fillet weld, which can be X-rayed to show a weld, but this is impractical in practice. Magnetic Particle Inspection (MPI) and Dye Penetration Inspection (DPI) can be used to validate welds.

ASME Standards
Socket weld flanges are not specified in class ASME 2500 according to the ASME B16.5 standard. The ASME B31.3 standard specifies that there should be approximately 1⁄16 inch (1.5 mm) clearance between the socket and the pipe end.

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