How do I inspect the quality of butt fusion welds?

TWI Frequently asked questions

by Chris Brown

The most common technique for inspecting the quality of butt fusion welds is visual inspection of the external weld bead, which should be smooth and have a symmetrical profile around the whole circumference. The alignment of the pipes/fittings should also be checked; the misalignment should not exceed 0.1 x nominal wall thickness.

The external weld bead (and sometimes also the internal weld bead) of a PE pipe butt fusion weld can also be removed using an appropriate de-beading tool, which removes the weld bead in one piece. The bead is then bent back manually at a number of locations along its length. If the two halves of the weld bead split apart, this indicates that there is contamination in the weld.

The technique will only detect fine particulate contamination, which is pushed out into the beads during the welding process. It will not detect embedded flaws or 'cold' welds and may not detect coarse particulate contamination.

For more critical applications, ultrasonic or radiographic non-destructive testing can be used to detect possible embedded flaws. TWI is a world-leader in the ultrasonic and radiographic inspection of butt fusion welds in PE pipes.

Further information

For further information on mechanical testing of welded joints in thermoplastics please contact TWI