Hydrogen Induced Cracking Observation by “in situ HIC Measurement Method”

Abstract

A new technique “in situ HIC Measurement Method” has been developed for measuring the HIC susceptibility more exactly. This technique is based on the combination of the electrochemical hydrogen permeation method and the automatic ultrasonic wave inspection system. The threshold hydrogen permeability (J_th×l) in segregated portion of line pipe steels decreased with the hardness of segregated portion. The diffusion coefficient of hydrogen (D) also decreased with the hardness. The threshold hydrogen content (C_th), which was calculated by the formula; C_th=J_th×l/D, was constant regardless of the hardness. On the other hand, the hydrogen content in steel (C₀), which was obtained by the formula; C₀=J×L/D, increased with the hardness, because the hydrogen permeation rate in a corrosive environment (J×L) was dependent on both the severity of the environment and the chemical composition of steel. Therefore it can be thought that the high HIC susceptibility is not attributed to the decrease in the C_th, but the increase in the C₀.