A radiant boiler having problems with chloride ingress began having many multiple failures of waterwall tubes, all with similar characteristics. The underlying mechanism was understood to be buildup of deposits containing chlorides (Under-deposit Corrosion) which would insulate the steel from the cooling water flow. The metal underneath the deposit would have been additionally weakened due to hydrogen embrittlement. The embrittled metal would fail either by corrosive attack or in this case by localised overheating.
Tags: Under-deposit attack