船用焊接B10铜镍环失效分析

Failure Analysis of a Weld Ring of 90/10 Cupronickel for Marine Pipe Combination

采用化学成分、宏观形貌、金相组织、微观及能谱分析等方法,分析了某船舶海水管路中的B10铜镍环的腐蚀失效原因。结果表明,在该铜镍环的腐蚀坑底部、冲刷腐蚀区、冲蚀坑内以及腐蚀穿孔的减薄区,都普遍存在着"冰糖块"状的晶间腐蚀形貌;优先腐蚀的晶界形成一个回路,被包围的晶粒发生了明显的脱镍和溶解;表层腐蚀产物及冲刷腐蚀区暴露出的晶粒上都存在S。该B10铜镍环的腐蚀破坏过程是含硫介质中的晶间腐蚀、脱成分腐蚀和冲刷腐蚀综合作用的结果。

A weld ring with rim of 90/10 cupronickel for marine pipe combination was corroded after 3 years operation. The failure of the ring was analyzed by means of chemical composition analysis, visual examination, metallographic observation of the alloy, as well as characterization of corrosion morphology and corrosion product by SEM/EDS. Results showed that intergranular corrosion was prevalent on the bottom of corrosion pits, in the erosion-corrosion zones and in the thinned region around corrosion perforations. De-nickelification and dissolution occurred in grains which were surrounded by the preferentially attacked boundaries. It was supposed that selective dealloy- ing and dissolution was related with the types of grain boundary and the grain orientations. Sulfide was detected on the surface of the corrosion product and on the facet of emerged grains on the erosion-corrosion zone. Therefore, the failure of the cupronickel ring was the result from the synergistic effect of intergranular corrosion, dealloying corrosion and erosion-corrosion in the sulfide-containing environment.