합금원소 및 2차상 입자 수준이 압력용기용 강재의 부식 및 수소취화 거동에 미치는 영향

다국어 초록 (Multilingual Abstract)

Recently, pressure vessel steels applied to the petrochemical industry suffer seriously from corrosion and hydrogen induced mechanical degradation problem. In particular, a sour environment with H2S gas tends to delay the hydrogen recombination reaction (H + H → H2) through the poisoning effect, this effect results in a large amount of hydrogen atoms influx into the steel matrix. In principle, hydrogen atoms formed on the steel surface caused by hydrogen reduction reaction continuously can diffuse through the steel matrix and can be trapped at some metallurgical defects. It can result in the cracking phenomena if the critical concentration of hydrogen atoms was exceeded. From these reasons, the steels applied in sour environment were required high resistance to hydrogen embrittlement. Although, there exists a considerable body vii of literature on hydrogen diffusion and embrittlement behaviors of the steels, the effects of alloying elements and 2nd phase particles on corrosion and corrosioninduced hydrogen embrittlement behaviors of pressure vessel steels have not been
accurately classified. In addition, conventional hydrogen permeation test to evaluate the hydrogen diffusion behaviors did not consider the experimental errors caused by the formation of corrosion scale on the steel surface during the permeation test.
Therefore, the present author has devised an analysis which can determine the fraction of reversible/irreversible trap site. In this study, HIC (Hydrogen induced cracking), SSC (Sulfide stress cracking), electrochemical polarization, immersion and hydrogen
permeation tests were performed to investigate the mechanism of corrosion induced hydrogen embrittlement behaviors. The results indicated that the steel with high C contents showed the high weight reduction and the low resistance to HIC. This is suggested that high C contents can increase the thickness of corrosion scale caused by high anodic dissolution of matrix and increase the internal diffusible hydrogen contents caused by high hydrogen reduction reaction. The steel with high Mo contents
increased the resistance to HIC by increasing additional irreversible trap site in the steel matrix. However, high Mo contents can decrease the stability of corrosion scale on the steel surface, resulting in decreasing the resistance to SSC. Therefore, the optimum contents of Mo should be determined. The steel with coarse-sized 2nd phase particles showed high sensitivity for hydrogen induced crack initiation. This indicated that coarse interface between 2nd phase and steel matrix can easily trap the hydrogen atoms exceeding the critical crack initiation hydrogen concentration.

목차 (Table of Contents)

• Ⅰ. 서론 1
• Ⅱ. 이론적 배경 5
• 1. 석유 화학산업 내 적용 강재의 종류 5
• 2. 압력용기용 강 재료의 분류 5
• 3. Sour 환경 내 강재 표면의 부식 현상 10
• 4. 수소 취화 이론 15
• 5. 압력용기용 강재의 수소 취성 파괴 현상 17
• 6. 합금성분이 내식성 및 수소 취화 현상에 미치는 영향 27
• Ⅲ. 실험 방법 31
• 1. 압력용기용 강재의 조성 및 시편 가공 31
• 2. 미세조직 및 2차상 입자 관찰 34
• 3. 확산성 수소량 측정 및 HIC, SSC 실험 35
• 4. 부식 특성 평가 45
• 5. 표면 부식생성물 분석 49
• 6. 전기화학적 수소확산거동 분석 50
• Ⅳ. 실험 결과 및 고찰 56
• 1. 미세조직 및 2차상 입자 분석 56
• 2. 확산성 수소량 측정 및 HIC 실험 63
• 3. SSC 실험 81
• 4. 부식 거동 분석 87
• 5. 표면 부식생성물 분석 97
• 6. 전기화학적 수소확산거동 분석 108
• Ⅴ. 결론 117
• Ⅵ. Summary 121
• Ⅶ. Acknowledgements 124
• Ⅷ. 참고문헌 125