Analysis of Stress Corrosion Cracking in Welded Joints of Q345R High-Pressure Air Cooler
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摘要: 某高压空冷器进气口换热管和管板胀管焊接处发生泄漏事故,通过宏观观察、机械拉断断口及裂纹面分析、金相组织分析、显微硬度测试、扫描电子显微镜(SEM)以及X射线能谱分析(EDS)等分析方法对泄漏失效处及关键位置材料进行检测和分析。研究发现高压空冷器进出口失效位置的裂纹均是由管箱内壁接头处向胀接间隙表面开裂,并且裂纹面能谱分析结果发现大量的S元素存在。结合管道受力情况、断口形貌、元素分析判定本次失效的模式为硫化氢应力腐蚀开裂(SSCC)。管内硫化氢为腐蚀源,在焊接残余应力集中和外载结构应力的协同作用下,焊趾发生SSCC开裂,裂纹沿着熔合线扩展至胀管外壁,发生泄漏失效。Abstract: A leakage failure occurred in the welded joint of the heat exchanger tube and tube plate in a high-pressure air cooler turbine. The leakage and critical positions are investigated by means of macroscopic observation, mechanical fracture and crack surface analysis, metallographic analysis, microhardness test, scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). It is found out that the cracks at the failure location expands from the welded joint of the tube box to the surface of the expansion gap, and that a large amount of S element is present at the crack surface. The failure mode is determined to be hydrogen sulfide stress corrosion cracking (SSCC) by combining stress, fracture morphology, and elemental analyse. Due to the hydrogen sulfide in the tube, and the synergistic effect of the stress concentration and structural stress by the external load, SSCC cracking occurs in the weld toe, and the cracks propagates along the fusion line to the outer wall of the expanded tube, leading to the leakage failure.
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Keywords:
- failure analysis /
- weld toe /
- stress corrosion
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