PWC – PREFERENTIAL WELD CORROSION

In the event of material decrease especially between the welded metal and the base material – i. e. in HAZ – Heat Affected Zone, it is called Preferential Weld Corrosion (PWC). The name is related to the situation where the base material decreases do not affect the pipes as much, because the corrosion “prefers” the material that was in contact with welding heat. Unlike the CUI, this process takes place from the inside, i.e. from the medium. Decrease of wall thickness may result in fatal failures even without major material decrease on the pipe itself.

PWC identification is not simple, because first the spots must be found that can be affected by the process, which is a task for corrosion and operation engineers. Another issue is the measuring, because the affected zone is very small, with inconvenient geometry, hardly accessible for usual ultrasound methods, incl. the thickness measuring devices. The most suitable methods are radiography, and ultrasound UT PA and UT TOFD.