To ensure defect free welding on critical jobs, DPT is applied for every pass of weld deposited. This is to weed out defects and other discontinuities which are to be removed by grinding.
Defects are revealed and identified by DPT when bleeding occurs on defective portion, and comes out on the surface for removal. The Heat Affected Zones (HAZ), where cracking might be present on heavy walls from 19.0mm and above thickness in piping, can also be revealed by DPT. This can only be performed through proper application, and by competent and certified level-II Technicians for this discipline.