What causes equipment to suffer from alkali embrittlement?

Alkali embrittlement usually occurs in high-temperature pressure-bearing components such as the boiler drum, as these components may meet all three conditions necessary for alkali embrittlement to occur: under normal operation, they are subjected to high temperatures and tensile stresses, while local areas such as the nozzles also experience uneven tensile stresses. As for the alkali concentration in the boiler water, although it does not reach a level that would cause alkaline embrittlement, local areas often experience an increase in the water’s alkali concentration due to the accumulation of sodium hydroxide. For example, in areas such as riveting, tube expansion, and other locations where gaps exist, once water enters, it tends to become increasingly concentrated, thus very likely reaching the concentration required for stress corrosion. Therefore, the majority of alkali embrittlement in the boiler drum occurs at the riveted or expansion-bonded joints.