Overview
Stainless steel pipe finish varies with environments. Knowing how environment will affect stainless steel pipes can help us make the right choice on stainless steel types, otherwise stainless steel pipes will also suffer from rust and corrosion. Different stainless steel pipes call for distinct surface treatment, such as:
- • Pickled finish or sand blasting finish for stainless steel seamless pipe (industrial use);
- • Polished finish for stainless steel sanitary tubes (seamless);
- • Polished finish for small diameter stainless steel welded tubes;
- • Pickled finish or sand blasting for stainless steel welded pipes and tubes (industrial use);
- • Inside and outside polishing for stainless steel sanitary tubes (welded).
Pre-treatments
Pre-treatments like pickling, chemical brightening, electrochemical polishing, electroplate, passivation, black coating, color coating, chemical machining, are the important steps to do surface treatment on stainless steel pipes. Before stainless steel pipe taking shape, the surface is likely to have oils, burs, uneven surface and oxide, hence, these flaws should be removed before doing surface treatment.
The dirt that needs to be removed from stainless steel pipe finish can be divided into organic matters and inorganic matters. Organic matters include mineral oil, such as diesel, machine oil, Vaseline, paraffin, animal oil and plant oil, such as bean oil, tea oil, colza oil, lard, and beef tallow. The greasy dirt is mainly lubricating oil, cutting oil, quenching oil, polishing oil, or fingerprints generated during stainless steel pipe processing. Inorganic matters include soil, dusts, compounds etc. generated during heat treatment.
Stainless Steel Pipe Pre-treatment Procedures
- (1) Polishing: Removing the roughness of stainless steel surface, doing machine lapping and polishing to certain surface finish;
- (2) Degreasing: Removing the surface oil;
- (3) Pickling: Removing the oxide on the surface;
- (4) Weak corrosion: activate surfaces to be treated, remove the surface passivation film, exposing the metal crystal structure.
Stainless Steel Pipe Surface-treatment Methods:
- (1) Mechanical Method: use polishing machine or other machines to remove surface roughness.
- (2) Chemical Method: use alkaline solution to remove oil, acid solution to pickle, and organic solvent to dissolve grease and descaling.
- (3) Electrochemical Process: use electrochemical to remove oils and do electrochemical etching.
- (4) Roll finish, centrifugal roll finish, centrifugal pan brightening, rotation brightening, suitable for small pieces with effects of flattening and descaling.
- (5) Sand blasting: applying for large area treatment, with effects of decontamination and removing oxide skin.
Hence, appropriate methods should be chosen as per the status of stainless steel pipe surface and the subsequent quality requirement.
