ACPD CRACK MICROGAUGE U10
Crack monitoring in laboratory fatigue tests can be successfully achieved using the alternating current potential drop (ACPD) technique. The technique has been used for many years in for example:
Crack Sizing Applications
- 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.
The ACPD Crack Microgauge Model U10(PD), for laboratory or service use, is a multi frequency instrument with high stability and resolution. It is now available with built in multiplexing as an option capable of extension to 128 channels. The Model U10(PD) can be used with a manual low inductance probe for individual investigations or with an array of fixed or spot welded connections to check on surface or weld toe regions. It can also be obtained with multiple frequency output for varying skin depths. Windows software is available for PC display of measurements to give fatigue crack growth curves, crack shape display, and even da/dN versus *K curves for standard specimen geometries.
The Model U10 system is packaged for crack monitoring applications and includes:
- ACPD Crack Microgauge (Model U10)
- Built in multichannel capability 128 channels
- Multi frequency capability
- Probe wire loom and field input connections
- Laptop computer
- Spot welder
The new range of ACPD instruments has become possible because of developments in electronics and computers and now provides instruments for crack sizing and monitoring on steel, stainless steels, nickel based alloys, titanium and even aluminium. The new instrument is available with a wide range of new manual probes, array monitors and software. It can be used with a PC or simply with the on-board micro-computer.
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. University College London have used the technique widely in specimen and component studies of fatigue crack growth including large scale tubular welded joints. Theoretical studies at UCL, on electrical field perturbation, have produced theoretical interpretations of the ACPD measurements eliminating the need for calibration. These solutions are incorporated into the TSC software thus giving immediate display of crack sizes.
The software available is Quick PD (QPD) and Flaw Location And Inspection in Real Time (FLAIR). QPD is like a computer based notepad which can export data to spread sheets for plotting or storage. FLAIR is more elaborate and can display graphically crack shape evolution and crack growth extension curves.
The main specification for the instrument is as follows:
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52 x 52 x 18 cm |
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24 kg |
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200 Hz, 1 kHz, 5 kHz |
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Up to 128 |
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110/240 V, 50/60 Hz |
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1 A |
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0 to +40 ºC |
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RS 232C |
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+10 VDC |
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No |
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