TWI Frequently asked questions
If the imperfections are surface breaking, they can be detected using a penetrant or magnetic particle inspection technique.
For sub surface imperfections, detection is by radiography or ultrasonic inspection. Radiography is normally more effective in detecting and characterising porosity imperfections. However, detection of small pores is difficultespecially in thick sections, and the effectiveness of the inspection technique will be affected by the material of construction.
Remedial action normally needs removal by localised gouging or grinding but if the porosity is widespread, the entire weld should be removed. Further inspection may be necessary to ensure that all traces of the porosity have beeneliminated. The joint should be re-prepared and re-welded as specified in the agreed procedure.
You can find more information on non-destructive testing in other parts of the JoinIT site.
For more information on porosity and how it can be detected and remedied, see Job Knowledge for Welders 42.
