TWI Frequently asked questions
Visual inspection is the most widely used technique for checking the quality of socket fusion welds, although radiographic inspection is sometimes used to detect internal voids.
The following inspection routine should be carried out once the weld is complete:
- Check that the beads between pipe and fitting are uniform on both sides of the joint. The beads should have no wrinkles or discontinuities
- Examine the weld beads for signs of contamination or degradation
- Check for misalignment between the pipe and fitting
- Examine the heated tool for signs of degraded material
If any of the above defects occur, the joint should be cut from the pipeline and remade. If a similar defect recurs, all further production welding should stop until the equipment has been thoroughly cleaned and examined.
The limitations of this type of visual inspection must be appreciated: a poorly formed bead may reliably indicate an unsatisfactory weld, but a correctly formed bead is not always a sure indication that the weld is satisfactory andfree from internal defects.
More information is available in Butt and socket fusion welding of plastic pipe - a guide to best practice
