The detection and sizing of circumferentially oriented stress corrosion cracking using axially oriented magnetic flux leakage inspection

摘要

Stress corrosion cracking(SCC)is a problematic phenomenon in line pipe as detection by many MFL inline inspection devices is not possible or has such high thresholds of detection it is insufficient to adequately identify threats before the next inspection cycle.In this paper we investigate the use of ultra-high frequency MFL sampling using Hall effect sensors to detect and characterize circumferentially oriented stress corrosion cracking(C-SCC).In pull tests, an axial flux direction magnetizer is used with 2.1 mm(0.083 in.)circumferential sensor spacing and sampling rates up to 4,000 Hz.Minimum detection criteria are estimated using excavated line pipe containing C-SCC, supported by laboratory testing and measurements.This inspection tool configuration proved capable of detecting in a small sample set circumferentially oriented SCC as small as 0.5 inches(12.5 mm)in length and 10% deep1.Sizing tests were conducted yielding 80% depth certainty tolerances consistently less than ±20% of wall thickness and 80% circumferential width tolerances consistently less than ±0.6 inches(15 mm).