Alternating Current Potential Difference (ACPD) is a crack sizing technique which can be used for monitoring and measuring fatigue crack length and depth.

It has been used for monitoring crack extension in laboratory tests and also for surface crack shape evolution studies.

The MK IV ACPD instrument can be used for a variety of crack sizing applications, including:

• Welded connections, butt welds, tee butts, tubulars, pressure vessels (refinery, nuclear, offshore topside and underwater)
• Threaded connections, nuts, bolts, drillstring threads, large diameter threads
• Automated inspection using tracking systems, robots
• Monitoring of cracks to give crack growth data
• Monitoring of critical regions for crack detection
• Turbine blades, blade roots
• Castings, forgings, ground repairs.

Studies at University College London, on electrical field perturbation, have produced theoretical interpretations of the ACPD measurements eliminating the need for calibration. TSC can advise on application of correction factors based on these results.