Analysis of the failed bolts of a small float head used for a heat exchanger was conducted by visual inspection,chemical composition analysis, metallographic examination, SEM observation and hardness test. The results showed that the microstructure and chemical composition of these bolts were in accordance with the relevant normals, and hardness was HRC30 - 32.5. The failure of the bolts was caused by wet HES stress-corrosion. Finally a logical safety countermeasure was proposed.
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