Surface damage treatment and polishing process of stainless

Large stainless steel flanges will rust under normal conditions (mainly on any surface), and free iron will rust and cause stainless steel corrosion. Therefore, it must be removed, floating powder can be removed with dust, some have strong adhesion, need to be treated with embedded iron.

 

In addition to dust, there are many sources of iron on the surface, including cleaning with ordinary carbon steel wire brushes and sandblasting with sand, glass beads or other abrasives. These Abrasives have previously been used for ordinary carbon steel, low alloy steel or cast iron. Or repair and polish the above non stainless steel products near the stainless steel flange and equipment. If the stainless steel flange is not protected during cutting or hoisting, the iron filings on the wire rope, spreader and working surface are easy to be embedded or dirty.

 

Surface damage treatment and polishing process of stainless steel flange

 

Stainless steel flange derusting method: immerse the flange in hydrochloric acid. The principle is to reduce rust, but this method has a certain risk. Hydrochloric acid is a corrosive substance, which is harmful to human body. In the process of operation, pay attention not to touch human body and use it with alkali, do not touch hands directly.

 

The existence of free iron can be prevented and found by inspection after fabrication. ASTM standard A380 [3] specifies the corrosion test method for iron or steel particles on stainless steel surface, which shall be used when there is absolutely no iron. If the results are satisfactory, clean the surface with pure water or nitric acid until the dark blue completely disappears. As stated in standard A380 [3], if the rust proof test solution cannot be completely removed, it is not recommended to use this test method on the process surface of the equipment. A simple test is to expose it to water for 12-24 hours to check for rust. This experiment is neither sensitive nor time-consuming. These are inspection tests, not cleaning methods. If iron is found, it needs to be cleaned by chemical and electrochemical methods.

Chemical degreasing → water washing → acid washing → water washing → chemical polishing → water washing → electrolytic polishing → water washing → passivation → water washing → drying → inspection.

 

Stainless steel flange gasket is divided into soft gasket and hard gasket. Generally, soft gasket is used for heating, natural gas and medium and low pressure industrial pipeline. If there is no special requirement for the thickness of the gasket, it is usually specified: 1.6mm for the diameter less than 125mm, 2.4mm for the stainless steel flange with the diameter greater than 125mm and less than 500mm, and 3.2mm for the flange larger than 500mm. High temperature and high pressure chemical pipeline uses hard gasket, namely metal gasket.

 

In the polishing process of stainless steel flange, some black oxide skin or American standard flange are easy to appear on the surface of stainless steel flange, which affects the application value of stainless steel flange. Only after mechanical polishing, chemical polishing and electrochemical polishing can it increase its own value.