Stainless steel pipe and other products will undergo forming, welding and heat treatment in the manufacturing process, which makes the surface contaminated. Therefore, the passivation treatment is an important and indispensable process. Basically there are following common methods in actual application.
Oxide skin removing and acid pickling
This is one of the most common indispensible forms in the process of manufacturing of seamless and welded stainless steel pipe in solid solution heat treatment state, the main purpose of which is to remove the oxide skin of inside and outside of stainless steel tube generated in solid solution or annealing heat treatment. Its high content of Cr subcutaneous caused by poor Cr layer will seriously affect the corrosion resistance. Formula of stainless steel pipe pickling solution is mainly chemical cleaning of hydrofluoric acid and nitric acid mixture, its concentration depending on the grade of steel and the content of Cr.
Mechanical removal of oxide skin
Implementing appropriate abrasive tools or abrasive to abrade oxide skin of the surface of the weld and its thermal oxidation discoloration in heat affected zone is common method used in the production of
stainless steel welded pipe. Tips for application:
This method is only applicable to welding state supply stainless steel welded pipe, especially stainless steel welded pipe with tendency of sensitization.
It is appropriate to adopt multichannel cross polishing from coarse to fine, with high requirements for corrosion resistance, after polishing spray or scrubbing method should be applied for local passivation treatment.
Soft acid purification
When only to remove the hard to avoid contamination of iron ion and other heterogeneous metals and their salts in the process of manufacture, storage or transportation, nitric acid or citric acid that do not contain hydrofluoric acid can be used for purification. In practice, increasing processing temperature will effectively shorten the processing time.
Electrolytic polishing
Electrolytic polishing is also called electrochemical polishing, a method without grinding adhesive material of the electrochemical surface and outstanding points of the metal itself. Its essence is exactly the same as electrochemical etching and electrochemical machining. This method can be used to make stainless steel surface colored.
