Two-Step Interpolation Algorithm for Measurement of Longitudinal Cracks on Pipe Strings Using Circumferential Current Field Testing System

Abstract

Pipe strings are critical facilities for well drilling, production, and transportation in oil and gas industry. Due to the stress corrosion cracking, longitudinal cracks are the most common defects on pipe strings. This paper presents a simple two-step interpolation algorithm based on a circumferential current field testing method for the measurement of longitudinal cracks on pipe strings. The theory and finite element method model of the circumferential current field testing method are analyzed. The two-step interpolation algorithm fitted by characteristic signals obtained from simulations is proposed to size longitudinal cracks. The first-step is to measure and calibrate the crack length by a quadratic polynomial interpolation formula and the second-step is to measure the crack depth by a cubic polynomial interpolation formula. Experiments are conducted to verify the efficacy of the proposed two-step interpolation algorithm based on the circumferential current field testing system. The results suggest that the two-step interpolation algorithm can obtain the length and depth information of longitudinal cracks effectively on pipe strings using the circumferential current field testing system.