溶融亜鉛めっき槽溶接継手部の不安定破壊強度に関する一考察

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A hot dip galvanizing bath in operation is under severe conditions because of the long-time contact with hot liquid zinc. As a result, many damages of galvanizing baths have been reported, such as corrosion, liquid metal embrittlement, creep deformation and creep rupture. The conditions of the galvanizing bath are particularly severe during the start-up operation, such as rapid temperature variation, thermal stress occurrence, increase of hydrostatic stress, corrosion and embrittlement by liquid zinc. In this report, the causes of unstable fracture, which has occurred at the welded joints of the side wall and bottom plate of a galvanizing bath, were investigated. The observation with SEM and analysis with EPMA were made at fracture initiation points. Moreover, heat transfer and stress FEM analyses were made. As results of investigations mentioned above, the following causes of the unstable fracture were obtained. (1) JIS SS400 steel with low Si content has been used for the bottom plate of the galvanizing bath. However, steel with low Si content (such as NAGP) should be used. (2) The beginning of the pouring of liquid zinc and liquid lead from the spare bath to the galvanizing bath was too early. That is to say, preheating time of the galvanizing bath was too short. (3) The bottom plate of the galvanizing bath must be completely covered with liquid lead before pouring liquid zinc. The bottom SS400 plate must avoid contact with liquid zinc. (4) The total pouring time of liquid zinc and liquid lead has been about an hour. However, longer pouring time is needed to prevent rapid increases of stress.
社団法人日本船舶海洋工学会の論文
2001-03-12

溶融亜鉛めっき槽溶接継手部の不安定破壊強度に関する一考察

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