PWC is preferential weldment corrosion. Inappropriate corrosion inhibitors applying program may aggravate the PWC. The inhibitor selection program should address the weldment issue to provide adequate protection over a facility’s design life cycle.
PWC is a term to describe the selective metal attack around the weldment, either in Heat Affected Zone (HAZ), weld metal or close by parent metals. The mechanism of corrosion is normally a combination of forming galvanic cells, weldment geometry and its associated flow. Inappropriate corrosion inhibitors and dosing methodology may worsen the corrosion by reversing the polarity of HAZ /Weldment/ Parent metals.
The inhibition effectiveness to mitigate with PWC can be used welding piece with electrically isolated segments of parent metal, HAZ and weldment. The test pieces are exposed to testing media and corrosion rates for each segment are assessed to reveal the overall effectiveness of the inhibitor.
from Volume IV of Shreir’s Corrosion