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What Are The Differences Between Socket Weld Fitting And Butt Weld Fitting

There are various ways for pipes, fittings, flanges, and valves to connect, socket weld and butt weld are the two popular. However, you might be confused about what are the differences between socket weld fittings and butt welding fittings, and which one would be best for your construction projects, as they all seem to have their pros and cons.

What is a socket weld

  • Socket welding (SW) is the welding method for inserting tubes. It is welded two pieces of a tube of different size, the smaller one is inserted into the larger one. The weld is completely around the periphery of the large pipe and is a fillet weld.
  • Socket welding components contain socket weld flanges and socket weld pipe fittings(contain socket weld 45/90 degree elbows, socket weld tees, socket weld caps, socket weld cross, socket weld coupling, socket weld union, socket).

What is butt weld

  • Butt welding is the corresponding welding of pipe and pipe fittings, pipe fittings and flanges or pipe and pipe fittings of the same diameter. The end of butt weld fittings shall be beveled.
  • Butt welding components contain weld neck flanges and butt welding pipe fittings(contain butt welding 45/90/180 degree elbow, butt welding tee, butt welding cap, butt welding bend, butt welding cross, butt welding reducer, wallet).

Different diameters of socket weld fittings and butt weld fittings

  • Socket weld is generally used for welding pipes, which are small in diameter. Commonly used specifications are diameters less than DN50 and the largest diameter is DN100 (or 4”). Butt weld is widely used for pipes with big and small diameters.

Different welding groove and welding seam of socket weld fittings and butt weld fittings

  • Usually, there should be a beveled end from 30 to 37.5° for butt welding to fill the welding bead. Of course, there will be a compound beveled end for super thick walls.
  • Socket welding doesn’t require a level, and it can directly weld the part. The socket weld seams are fillet welds.
  • Considering the factor of the strength of the weld, the force condition, and so on, butt welding is better than socket welding.

Different non-destructive testing of socket weld fittings and butt weld fittings

  • The non-destructive testing methods for socket welding are magnetic particle testing(MT) and penetrant testing(PT). Magnetic particle test is used for carbon steel parts and penetrant test is used for SS parts. Butt welding requirements are higher than socket welding requirements as well as the testing requirements. The butt welding shall be 100% tested to ensure no leakage and it is necessary to do a radiographic inspection.

Different prices of socket weld fittings and butt weld fittings

  • Normally, the price of socket weld fittings is higher than butt weld fittings of similar size, butt welding fitting need extra more cost because it would also be more difficult to weld and fit up properly. It would therefore require more time and the experience of experienced welders.
  • Socket weld is easy to install. But it requires approx 1/16″of gap at the bottom of the pipe to socket into, to allow thermal expansion. This gap can lead to overstress problem that cracks the fillet weld of the fitting. Socket weld is troublesome in corrosive fluid service due to crevice corrosion. And it is easy to corrode due to the discontinuity of the smooth pipe internals.

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