Direct Current Potential Drop 

DC-PDDirect Current Potential Drop is an electromagnetic NDT method, where a constant electric direct current is passed between two contacts placed on the component under test. The presence of a defect between the contacts increases the electrical resistance and hence there is a change in potential (voltage) when compared to a defect-free part of the component. This change, ie the difference in voltage between A-B and C-D in the Figure, is used to detect and size defects.

An alternating current can be used (AC-PD), giving a different response and sensitivity profile due to the electromagnetic skin effect. DC-PD is typically used for in-situ monitoring of crack growth in materials testing laboratories but has been used for monitoring creep damage and corrosion.

More information on direct current potential drop can be found in the following article:
‘The potential drop technique and its use in fatigue testing: A short applications note’, Matelect. (Available at: www.matelect.com/files/Download/PDfatigueApp.pdf)

For more on alternating current potential drop see:
‘ACPD: Alternating current - potential drop’, BINDT. (Available at: www.bindt.org/What-is-NDT/Index-of-acronyms/A/ACPD)

WHAT THE HEC?! articles are not intended to be the definitive account on the topic or acronym in question. Readers’ comments and contributions are welcomed. Email: ndtnews@bindt.org