Caustic means corrosive or destructive. The corrosive action of caustic soda (NaOH) is evident in metal equipment such as boilers when operating in alkaline medium caused by high pH level of the water. Embrittlement due to the presence of caustic soda happens due to susceptibility of the material, presence of concentrated hydroxide and tensile stress such as around riveted holes. When liquid evaporates, salts are deposited in crevices and around rivet heads.
The stress near the riveted hole combined with the presence of alkalis can cause cracking of the boiler shell.
Trenchlesspedia Explains Caustic
Embrittlement of the material due to the presence of caustic soda can be prevented by controlling stress levels, avoiding use of material that is prone to caustic corrosion and avoid using alkalis. Pipelines damaged due to caustic corrosion can be identified using trenchless inspection methods and the damaged pipelines can be repaired using trenchless rehabilitation methods. Trenchless methods of repair are cost and time effective because they eliminate the need to dig up the roads or sidewalks and can be carried out from manholes. Some methods include cured-in-place pipe (CIPP), mechanical spot repair and thermoformed pipe.
The materials used in trenchless repair such as high density polyethylene (HDPE) and polyvinyl chloride (PVC) are favored materials for trenchless rehabilitation of pipes because of their resistance to corrosive environment and long problem free service life.