1, dust

Production is often carried out in dusty venues, the air often with a lot of dust, they continue to fall on the surface of the device. They can be removed with water or alkaline solution. However, the adhesion of the dust needs high-pressure water or steam to clean up.

2, float iron powder or embedded iron

On any surface, free iron will rust and corrosion of stainless steel. Therefore, it must be cleared. Float powder can be removed with dust together. Some adhesion is very strong, must be embedded iron processing. In addition to dust, the surface of the iron a lot of sources, including the use of ordinary carbon steel wire brush cleaning and previously used in carbon steel, low alloy steel or cast iron on the use of sand, glass beads or other abrasive shot peening, or In the vicinity of stainless steel pipe parts and equipment on the previously mentioned non-stainless steel products for grinding. In the process of cutting or hanging if the stainless steel does not take protective measures, wire rope, spreader and work surface iron is easy to insert or tarnish the surface.

Ordering requirements and post-production inspections can prevent and detect the presence of free iron, and ASTM Standard A380 [3] specifies a rust test for inspecting stainless steel surface iron or steel particles. This method should be used when it is absolutely impossible to have iron. If the results are satisfactory, the surface is washed with clean pure water or nitric acid until the dark blue is completely gone.

As indicated by standard A380 [3], if the rust test solution can not be completely cleaned, it is not recommended to use this test method on the surface of the process, ie the direct contact surface used to produce human consumer products. A relatively simple test method is exposed in water for 12 to 24 hours to check for rust spots. This test is less sensitive and time consuming. These are test tests, not cleaning methods. If iron is found, it must be cleaned up by the chemical and electrochemical methods described later.

3, scratches

In order to prevent the process lubricant or product and / or dirt from accumulating, scratches and other rough surfaces must be mechanically cleaned.

4, stainless steel tube heat back to the color and other oxide layer

If the stainless steel is heated in the air to a certain high temperature during the welding or grinding process, both sides of the weld, the lower surface and the bottom of the weld will appear chromium oxide thermal recovery color. The thermal recovery color is thinner than the oxidation protection film and is clearly visible. The color depends on the thickness, can be seen rainbow color, blue, purple to light yellow and brown. Thicker oxides are generally black. It is due to high temperature or long time at a higher degree due to stay. When any such oxide layer is present, the chromium content of the metal surface is lowered, resulting in a decrease in the corrosion resistance of these regions. In this case, not only to eliminate the heat back to the color and other oxide layer, but also the lower chromium metal layer they should be cleaned.

5, rust spots

Before or during the production process sometimes see the stainless steel products or equipment on the rust, indicating that the surface is seriously polluted. The rust must be removed before the equipment is put into use and the thoroughly cleaned surface should be tested by iron and / or water tests.

6, rough grinding and machining

Grinding and machining will cause rough surface, leaving the groove, overlap and burr and other defects. Each defect may also damage the metal surface to a certain depth, so that the damaged metal surface can not be cleaned by pickling, electro-polishing or shot peening. Rough surface can be the source of corrosion and deposition of the product, before the weld to clean up the weld defects or remove the excess weld reinforcement can not be rough grinding. For the latter case, should be re-grinding with fine abrasive.

7, welding lead marks

Welders in the metal surface arc, will cause rough surface defects. The protective film is damaged, leaving a potential source of corrosion. The welder should be arcned on the already welded bead or on the side of the weld joint. And then the traces of the arc into the weld.

8, welding splash

Welding splash and welding process has a great relationship. For example: GTAM (gas shielded tungsten arc welding) or TIG (inert gas protection tungsten welding) did not splash. However, the use of GMAW (gas protection metal arc welding) and FCAW (with solder core arc welding) two welding process if the welding parameters used improperly will cause a lot of splash. When this happens, you must adjust the parameters. If you want to solve the problem of welding splash, welding should be painted on each side of the splash agent, so you can eliminate the splash of adhesion. After welding, it is easy to clean up this splash and various spatter, without damaging the surface or causing minor damage.

9, flux

The welding process using flux is manual welding, with solder core arc welding and submerged arc welding. These welding processes leave small flux particles on the surface, and the ordinary cleaning method can not remove them. This particle will be a corrosive source of crevice corrosion and must be mechanically cleaned to remove these residual fluxes.

10, welding defects

Welding defects such as: undercut, not penetration, dense pores and cracks not only reduce the stability of the joints, but also become a corrosive corrosion source of corrosion. When this is done to clean up the results, they also entrain solid particles. These defects can be repaired by re-welding or refilling after refilling.

11, oil and grease

Organic substances such as: oil, grease and even fingerprints will become a local corrosion source of corrosion. Because these substances can act as a barrier, they will affect the chemical and electrochemical cleaning effect, and therefore must be thoroughly cleaned up. ASTM A380 has a simple water cut (WATERBREAK) test to detect organic contaminants. During the test, water is poured from the top of the vertical surface and the water is separated from the surroundings of the organic matter during the downward flow. Flux and / or acid chemical cleaning agents can remove oil traces and grease.

12, residual adhesive

When the tape and protective paper are torn off, there is always a portion of the adhesive that remains on the surface of the stainless steel. If the adhesive agent is not hard, you can use organic flux to remove. However, when exposed to light and / or air, the adhesive is hardened to form a corrosive source of corrosion. And then need to use fine abrasive for mechanical cleaning.

13, paint, chalk and marker pen

The effects of these contaminants are similar to those of oil and grease. It is recommended to use a clean brush and clean water or alkaline cleaning agent to wash, you can also use high pressure water or steam rinse.