Stress Corrosion Cracking Initiation Behavior of Weldable Structural Steel in <TEX>$H_2S$</TEX> Gas Saturated HCl Solution

J. Ocean Eng. Technol. 1990;4(1):88-100.

Stress Corrosion Cracking Initiation Behavior of Weldable Structural Steel in $H_2S$ Gas Saturated HCl Solution

$H_2S$ 가스포화 염산수용액에 의한 용접구조용강의 응력부식균열 발생거동

오세욱,김재철,김광영

동아대학교 기계공학과,동아대학교 기계공학과,한국기계연구소

Keywords: Stress Corrosion Cracking, Hydrogen Damage, Compliance Formula, Inclusion, Segregation, $K_{ISCC}$, SCC

핵심용어: 응력부식귀열, 수소손상, 컴플라이언스수식, 개재물, 편석, 응력부식 하한계 응력확대계수

Abstract

Among the test methods to evaluate stress-corrosion cracking(SCC) on the basis of fracture mechanics, constant displacement(bolt) loading method using modified-WOL specimen is practically convenient. In this test method, compliance formula is generally required to calculate load(consequently $K_{ISCC}$). There are many problems in using the analytic compliance formula to calculate $K_{ISCC}$, so we had proposed the experimental $K_{ISCC}$ evaluation technique in the previous report. This study has employed the slightly altered configuration of modified-WOL specimen made of weldable structural stee(BS360-50D). With these specimens, stress-corrosion tests have been performed in $H_2S$ gas saturated 20% HCl solution. Through the test, the problems as mentioned earlier have been discussed again, and the proposed evaluation technique has been verified. And the stress-corrosion cracks and hydrogen blisters have been investigated in the initiation step with the aids of metallurgical micrographs, SEM fractographs, and EPMA analysis. The inclusions segregated in the mid-thickness region traps hydrogen to produce the hydrogen blistering. The applied or residual stress does not contribute the occurrence of the blister. Hydrogen absorbed into the mid-thickness region is consumed to produce the blistering so that stress-corrosion crack could hardly be detected at that region. The stress-corrosion cracks initiate from the inclusions and propagate in radial pattern. And the initiation site is remote from the crack tip and is inclined from the crack plane, which is assumed to be caused by the triaxial stress and the amount of the absorbed hydrogen.