Do devices with a surfacing structure inside require pickling? CrMo steel + 347
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Do devices with a surfacing structure inside require pickling? Why? The material is CrMo steel + 347.
Stainless steel 347 has good resistance to intergranular corrosion and is suitable for use in environments prone to such corrosion. As for pickling, it is not only necessary but also followed by passivation.
Those prone to intergranular corrosion should be pickled and passivated
Why is pickling necessary? According to GB150.4 and relevant regulatory requirements, pickling must be carried out only as specified in the design documents.
Experts say that a dense oxide film forms on the surface during welding, which provides protection and eliminates the need for pickling.
Both the Fixed Volume Specification and GB150 require that the surfaces of stainless steel with corrosion resistance requirements be pickled and passivated. The use of cladding material is certainly intended to enhance corrosion resistance; the fact that this is not specified in the design documents constitutes a design omission.
The key is that I called the design institute myself, and they said acid cleaning wasn’t necessary, as surfacing does not fall under composite plate equipment.
In my opinion, passivation is a prerequisite for pickling, and not all stainless steels will undergo passivation to form a passive film in the pickling solution.
Of course, for intergranular corrosion agents, pickling and passivation cannot prevent intergranular corrosion from occurring; they can only delay it. If there is a clear answer in the design, it is possible to proceed without pickling, but considering the appearance of the equipment, it is still better to carry out pickling.
I reviewed the technical specifications for single- and double-layer surfacing in several design institutes (in Beijing and Luoyang), and none of them mentioned acid cleaning. There are many testing procedures involved in various inspections as well as in the pre-welding process evaluation, but nothing was said regarding acid cleaning after welding.