Determination of Pipe Wall Thickness using the Four-point Probe Technique

• Published in: Hi-hakai kensa Vol. 61; no. 10; pp. 545 - 552
• Main Author: YAMASHITA, Masato
• Format: Journal Article
• Language: Japanese
• Published: Tokyo The Japanese Society for Non-Destructive Inspection 01.10.2012; Japan Science and Technology Agency
• Subjects: Electrical resistivity; Four-point probe technique; Graphite; Inspection; Laplace’s equation; Mathematical analysis; Mathematical models; Nondestructive testing; Pipe; Pipe wall thickness; Pipe wall thinning; Poisson’s equation; Potential drop technique; Resistivity correction factor; Wall thickness
• ISSN: 0367-5866
• DOI: 10.11396/jjsndi.61.545

The remaining wall thickness of circular pipes is non-destructively determined using two electrical quantities of pipe material, namely, resistivity ρ and resistance R. These quantities are measured using the four-point probe technique and are related to the equation ρ = FaR, where a is the outer radius and F is a correction factor. Since the correction factor contains the inner radius as a variable, we can obtain the inner radius of thinned pipe by numerically solving the equation substituting resistivity of the initial pipe for resistivity of the thinned pipe. The starting specimen, which is made from isotropic graphite, has a form of 11.5 mm outer radius, 52.4 mm length and 8.01 mm wall thickness. Other specimens, having thinner wall thickness, are successively machined from the inner surface of the starting specimen. Comparison of the calculated wall thickness with wall thickness measured using an inner digital micrometer shows that the difference between them is in the range of 0.6 mm for all specimens.