Causes of head cracking of high-temperature and high-pressure J-type dyeing machine

The head of a high-temperature and high-pressure J-type dyeing machine was cracked. Causes of head cracking were analyzed through methods such as macro observation, chemical composition analysis, metallographic inspection, scanning electron microscopy and energy spectrum analysis. The results showed that the content of chloride ions in dyeing solution in J-type dyeing machine was relatively high. The chloride ions accumulated in the R part of head, which damaged the passivation film on the inner surface and caused pitting corrosion. Under the combined action of working stress inside head and residual stress generated during cold working of head, the pitting corrosion spread into macro cracks, which eventually led to stress corrosion cracking of head.