The testing and evaluation method for magnetization characteristics of strain aged 20G steel

The 20G high-pressure pipe is widely used in fertilizer plants and other enterprises. Pipe failures, even explosion accidents, are caused by the strain aging embrittlement. The magnetic characteristics were studied in the process of 20G strain aging. It was found that after plastic deformation, coercive force, remanence, and hysteresis loss increased and the maximum differential permeability decreased. The internal stress of the material was released when aging treatment occurred. The material, physical, and chemical test results were combined and the coercive force which had the biggest change magnitude, strongest direction, and highest measurement accuracy was selected as the characteristic parameters. Based on the impact absorbing energy and criteria impact fracture analysis results, a nondestructive testing scheme for detecting the degree of strain aging embrittlement was obtained.