低合金高强钢焊接构件在高温锅炉水中的应力腐蚀开裂行为研究

分析了某公司的2#乙二醇R-120环氧乙烷反应器中C-11环焊缝开裂原因。对开裂C-11环焊缝开展了化学成分、金相观察、硬度测试、断口微观观察、EDS能谱分析等试验研究。试验发现：壳程、管板母材和焊缝金属化学成分分别满足SA543 Type B CL.1,SA508 Gr.4N CL.1和MGS 80的要求;从内壁管板侧热影响区起裂的主裂纹穿晶扩展,裂纹尖端沿晶扩展并有分叉,具有应力腐蚀裂纹特征;内壁附近焊缝两侧热影响区局部有马氏体组织;管板侧热影响区硬度最高为466.3 HV10;断口观察发现裂纹在内壁产生,是多源裂纹,沿壁厚向外壁扩展15 mm,断口上有冰糖状等轴晶和柱状晶;裂纹断口探测到P和Na元素。该反应器开裂原因是由于焊接导致在管板与壳程焊接区域存在较高的残余应力,在高温锅炉水介质中,发生了应力腐蚀开裂,由内壁向外扩展,最终导致泄漏。

Investigation on Stress Corrosion Cracking Behavior of Weld Joint of Low Alloy Steels with High Strength in High Temperature Boiler Feed Water

The reason of leak of weld joint （ C - 11 ） of EO reactor of a company was analyzed experimen- tally. The weld joint （ C - 11 ） was investigated by optical emission spectrometry, optical microscopy , hardness tester, scanning electron microscopy equipped with energy- dispersive X -ray spectroscopy. It showed that the chemical composition of shell plate, tube sheet and weld is consistent with specification of SA543 Type B CL. 1 ,SA508 Gr. 4N CL. 1, and MGS 80, respectively. The transgranular crack initiated from the HAZ of tube sheet side near inner surface propagated outwards, and the crack tips with their braches expanded along the crystalline, which has the stress corrosion crack characteristic. The martens- ite organization was observed in the HAZ near the inner surface. The highest hardness in the HAZ adja- cent to tube sheet is 466.3 HV10. The fracture observation showed that crack is the multiple source cracks, expands 15 mm along wall thickness outwards, and equiaxed and columnar crystals were found on the fracture. The elements of P and Na were detected on the fracture surface. It can be deduced that the stress corrosion cracking in high temperature water occurred because of high welding residual stresses, the leak of weld joint （ C - 11 ） of EO reactor took place eventually.