Pickling and passivation of chromium-molybdenum steel
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For high-temperature and high-pressure steam pipelines, 15CrMo and 12CrMoV are the two materials used; is it necessary to carry out pickling and passivation treatment on the welded joints after construction?
The standard isn’t in hand, but it shouldn’t be needed. The chromium-molybdenum steel is primarily a heat-resistant steel, and pickling and passivation are generally used as rust prevention treatments.
What was said upstairs is correct; pickling and passivation are processes applied to stainless steel materials, with the aim of creating a passivation layer on the surface of the steel to protect the material itself. Is the pickling mentioned by the original poster referring to the use of acid to remove rust and oxide scale from the surface of steel? Since pickling is not suitable for removing oxide scale from chromium-molybdenum steel, it often increases the hydrogen content in the steel, leading to hydrogen embrittlement; therefore, it is not recommended to use pickling to eliminate the rust layer on the surface of steel.
The outer surface of the welded joint does not require pickling or passivation treatment. If your steam pipes lead to moving equipment such as turbines, the pipes must be purged with steam and pass inspection tests before they can be put into use. After steam purging, in order to reduce the purging time, acid cleaning of the pipe interior can be carried out first.