Early Inspection of Wet Steam Generator Tubes Based on Metal Magnetic Memory Method

Abstract

Fatigue tests on wet steam generator 20G tubes were carried out and the metal magnetic memory (MMM) signals were detected. Though the analysis of MMM signals from different fatigue cycles, the variation characteristic of the MMM signals was obtained and a novel quantitative evaluation method of the early failure by MMM technology was proposed and applied in oilfield on-site test finally. The test results showed that MMM method can effectively locate the stress concentration zone (SCZ). The magnetic gradient indicates the damage severity of the investigated zone of the tube. If the magnetic gradient is above 12A/(m·mm), this zone is damaged seriously.