Potential drop monitoring of creep damage at a weld

Corcoran, Joseph; Nagy, Péter B.; Cawley, P.

doi:10.1063/1.4940625

Cited by 4 publications

(4 citation statements)

References 9 publications

(13 reference statements)

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“…A square configuration of electrodes was welded to the surface of a tensile test specimen as illustrated in Figure 7. This measurement configuration is relatively arbitrary as similar behaviour will be present with different electrode configurations in ferromagnetic materials; the square arrangement is utilised for creep strain measurements [19], [34]. The test component was formed from S275 steel with cross section of 75 mm x 24 mm.…”

Section: Suppression Of the Skin Effectmentioning

confidence: 99%

“…A similar measurement arrangement to that described in Section 4.1 Figure 7 was produced; a square configuration of electrodes was welded to an S275 steel component though this time the electrode separation was 10 mm and the component dimensions were 25 x 100 x 100 mm; the resulting transfer resistance is approximately 2 μΩ. This is an equivalent measurement arrangement to that proposed for creep strain measurement in [19], [34], though on this occasion measurements will be taken on a roomtemperature, unloaded component for ease of comparison.…”

Section: Enhanced Noise Performance and Low Power Operationmentioning

confidence: 99%

“…Recently, a novel quasi-DC approach to materials testing has been developed that overcomes many of the issues with the conventional DC or AC techniques. Previous literature [19], [32]- [34] has concentrated on the advances in material testing that are enabled by the technique while the present paper is focussed on the technical background of the concept and on details of the measurement system required for operation in the demanding transitional regime between DC and AC measurements.…”

Section: Introductionmentioning

confidence: 99%

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A Quasi-DC Potential Drop Measurement System for Material Testing

Corcoran

Davies

Cawley

et al. 2020

IEEE Trans. Instrum. Meas.

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Potential drop measurements are well established for use in materials testing and are commonly used for crack growth and strain monitoring. Traditionally, the experimenter has a choice between employing direct current (DC) or alternating current (AC), both of which have strengths and limitations. DC measurements are afflicted by competing spurious DC signals and therefore require large measurement currents (10's or 100's of amps) to improve the signal to noise ratio, which in turn leads to significant resistive Joule heating. AC measurements have superior noise performance due to utilisation of phase-sensitive detection and a lower spectral noise density, but are subject to the skin-effect and are therefore not well suited to high-accuracy scientific studies of ferromagnetic materials. In this work a quasi-DC monitoring system is presented which uses very low frequency (0.3-30 Hz) current which combines the positive attributes of both DC and AC while mitigating the negatives. Bespoke equipment has been developed that is capable of low-noise measurements in the demanding quasi-DC regime. A creep crack growth test and fatigue test are used to compare noise performance and measurement power against alternative DCPD equipment. The combination of the quasi-DC methodology and the specially designed electronics yields exceptionally low-noise measurements using typically 100-400 mA; at 400mA the quasi-DC system achieves a 13-fold improvement in signal to noise ratio compared to a 25A DC system. The reduction in measurement current from 25A to 400mA represents a ~3900 fold reduction in measurement power, effectively eliminating resistive heating and enabling much simpler experimental arrangements.

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Section: Suppression Of the Skin Effectmentioning

confidence: 99%

Section: Enhanced Noise Performance and Low Power Operationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Quasi-DC Potential Drop Measurement System for Material Testing

Corcoran

Davies

Cawley

et al. 2020

IEEE Trans. Instrum. Meas.

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“…The NDE application of particular interest is the potential drop creep strain sensor for use in high-temperature, highpressure, static power station components [6,7,13]. A square configuration of electrodes is permanently attached to the surface of a component.…”

Section: Introductionmentioning

confidence: 99%

Compensation of the Skin Effect in Low-Frequency Potential Drop Measurements

Corcoran

Nagy

2016

J Nondestruct Eval

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Potential drop measurements are routinely used in the non-destructive evaluation of component integrity. Potential drop measurements use either direct current (DC) or alternating current (AC), the latter will have superior noise performance due to the ability to perform phase sensitive detection and the reduction of flicker noise. AC measurements are however subject to the skin effect where the current is electromagnetically constricted to the surface of the component. Unfortunately, the skin effect is a function of magnetic permeability, which in ferromagnetic materials is sensitive to a number of parameters including stress and temperature, and consequently in-situ impedance measurements are likely to be unstable. It has been proposed that quasi-DC measurements, which benefit from superior noise performance, but also tend to the skin-effect independent DC measurement, be adopted for in-situ creep measurements for power station components. Unfortunately, the quasi-DC measurement will only tend to the DC distribution and therefore some remnant sensitivity to the skin effect will remain. This paper will present a correction for situations where the remnant sensitivity to the skin effect is not adequately suppressed by using sufficiently low frequency; the application of particular interest being the in-situ monitoring of the creep strain of power station components. The correction uses the measured phase angle to approximate the influence of the skin effect and allow recovery of the DC-asymptotic value of the resistance. tial drop measurements are minimum phase is presented and illustrated on two cases; the creep strain sensor of practical interest and a conducting rod as another common case to illustrate generality. The correction is demonstrated experimentally on a component where the skin effect is manipulated by application of a range of elastic stresses.

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