NEWS

After the civil construction project of a high-rise apartment was completed, all the stainless steel guardrail of the outer windows were installed, and the water, electricity, heating, and ventilation installation and exterior wall decoration engineering construction began.At the same time, the internal hardcover was inserted.Half a year later, the overall project was basically completed.During the cleaning, it was found that many parts of the stainless steel window guardrail installed in the early days were collided, scratched and corroded, with rust spots or black skin.In this regard, everyone was very surprised. How could stainless steel rust?Is there a problem with the stainless steel material?To this end, I collected some information about stainless steel and removed the corroded rust spots, oxide skins and other defects on the stainless steel window guardrail. Until the project was delivered for acceptance, there was no recurrence.

01 What is stainless steel

Stainless steel is an alloy steel containing a certain amount of chromium, which has unique strength, high wear resistance and superior corrosion resistance.The main element that determines that stainless steel has the above characteristics is chromium.Because after chromium is added to the steel, its internal structure is promoted to develop in a way that is conducive to resisting corrosion and damage, and it has the ability to resist external corrosion.

Common stainless steels are chromium stainless steel, which contains more than or equal to 12% chromium; there are also different types of stainless steels such as nickel-chromium stainless steel, which contains more than or equal to 18% chromium and contains a certain amount of nickel.Nickel is an excellent corrosion-resistant material.However, alloy steels containing nickel alone cannot form stainless steel, because this corrosion resistance can only be exerted after nickel and chromium are combined.Nickel and chromium are present in stainless steel at the same time. Stainless steel has many more valuable properties. The reason is that nickel can change the structure of chromium steel, so that the corrosion resistance and process performance of stainless steel can be improved.Most of the stainless steels commonly used in construction projects are nickel-chromium stainless steels.

Will stainless steel rust?The answer is yes.When rust spots appear on the surface of stainless steel, many people will be surprised, thinking that stainless steel will not rust at all. If it is rusty, it is not real stainless steel.In fact, this is a one-sided view.For example, gold generally does not rust at room temperature because its structure is very stable.But it should be noted here that under the “normal” circumstances mentioned here, that is to say, under good maintenance; but if you put it outdoors in the wind and rain, it will also encounter chemical reactions such as hydrochloric acid and rust spots.Therefore, the rust problem of stainless steel, excluding material problems, is mostly caused by improper human operation or maintenance.

02 Why does stainless steel rust?

Stainless steel is corroded because of its special internal structure and surface oxide film (Cr2O3), which makes it more difficult to react chemically with the medium under normal circumstances.But it is not that it will not be corroded under any conditions. In other words, the corrosion resistance of stainless steel is relative, not absolute.In the case of the presence of corrosive media and rust at the same time, stainless steel can also be corroded by slow chemical reactions or other reactions with corrosive media.Under some conditions, the corrosion rate is relatively fast and rust occurs.Stainless steel is protected by a smooth, extremely thin, strong and stable oxide film (Cr2O3) formed on the surface to prevent the continued infiltration and oxidation of oxygen atoms and obtain corrosion resistance.However, for some reasons, once this protective film is destroyed, the oxygen atoms in the air or liquid continue to penetrate and the iron atoms inside continue to precipitate to form iron oxide and rust.During construction, the surface of stainless steel is scratched and the protective film is damaged due to defects such as residues during processing and cutting, splashes during welding, and bites, pores, cracks in the welding area, or contact with carbon steel parts and other sharp objects. Rust.In addition, the rust of stainless steel has a lot to do with the environmental conditions in which it is used.Under normal circumstances, stainless steel is corrosion-resistant.However, when the air contains a large amount of chlorine media such as salt, sulfuric acid, hydrochloric acid, oxalic acid, detergents or alkalis such as cement, lime and other impurities, it will also corrode and destroy the surface protective film, causing stainless steel corrosion.

03 Problems that should be paid attention to in the production and installation of stainless steel parts

1.Whether it is stainless steel parts, raw materials or processed parts, during transportation, loading and unloading, special hoisting means of transportation should be used to avoid contact between stainless steel and wire ropes or other hard carbon steel, so as not to hurt or scratch its surface.  

2. The processing site of stainless steel parts should be relatively stable, and the workbench should be covered with rubber sheet cushions to avoid damage to the stainless steel surface. 

3. When cutting stainless steel parts, the plates should be cut by shear or plasma cutting; pipes and other profiles should be cut by plasma cutting or sawing.When cutting, rubber-based soft pads should be laid to avoid damage to its surface; after plasma cutting, the cutting slag should be cleaned up in time; when sawing, the clamping place should be protected by pads.Clean up the oil stains, residues, etc. at the sawing place in time after sawing.

4. Before stainless steel parts are installed and welded, they must be carefully cleaned of oil, dust and other debris on their surface.Argon arc welding should be used as much as possible when welding.If manual arc welding is used, fast welding with low current is applied, and it is strictly prohibited to draw arcs in non-welding areas.The ground wire used should be selected in an appropriate location and firmly connected to avoid the arc burning the surface or the burn area is too large; anti-splash measures should be taken during welding.When cleaning up the welding slag after welding, a stainless steel flat shovel should be used, and a carbon steel flat shovel should not be used.The welds should be carefully polished so that the welds have a smooth transition from the surface of the base material, and there must be no quality defects such as slag, pores, bite edges, splashes, cracks, and unfused. 

5.After the welding of stainless steel parts is completed, the surface should be cleaned in time.

(1) The oil and dust on the surface of stainless steel parts should be carefully wiped and cleaned with neutral water.

(2) If the surface of stainless steel parts is damaged by splashes, cutting slag, scratches, etc., it must be carefully and thoroughly polished.When grinding, you can use a portable grinder to install the finest grinding wheel and grind it carefully. Be careful not to over-grind to avoid additional scratches.

(3) Apply appropriate soft polishing tools to the surface of the cleaned and polished stainless steel parts to polish them, so that the surface of the damaged stainless steel parts reacts with the oxygen in the air to form a new protective film.When polishing, it is required to be uniform and consistent, and to avoid over-polishing and scratches.When removing the black oxide skin on its surface and polishing, some paraffin wax can be applied to the place that needs to be polished for better effect.When cleaning or polishing the surface of stainless steel parts, choose a day when the weather is clear and the air is relatively dry.This is because in clear and dry weather, the surface of stainless steel parts that remove rust spots can quickly react with oxygen in the air to regenerate a new Cr2O3 protective film. After the surface treatment of stainless steel parts is completed, care should be taken to protect the finished product, avoid touching by personnel, and avoid secondary pollution such as oil and dust.

04 Other precautions for stainless steel engineering construction

1.When purchasing stainless steel raw materials, the performance of the raw materials should be carefully mastered, and the applicable stainless steel type should be selected according to the use environment. It is recommended to buy products certified by major brands and authoritative institutions to ensure quality while also enjoying after-sales service.

2. Choose raw materials with smooth surface, high finish, and no defects such as heavy skin, clamped skin, and sand eyes. 

 3.The installation of stainless steel parts should be arranged as much as possible after the completion of other projects to avoid construction pollution and damage.

 During the use of stainless steel parts, if the stainless steel parts are corroded and rusted, oxidized black skin or the surface protective film is scratched, the above methods can also be used for removal and polishing.

Stainless steel protects us from wind and rain, and guards our family at all times, so we need to pay more attention to the daily maintenance and maintenance of stainless steel anti-theft windows, guardrails and stainless steel doors.；

1.Under normal circumstances, pay attention to keeping the plate and pipe surfaces clean and dry. This is the most direct and simple way to prevent stainless steel from rusting.In the dry season, you only need to clean up the dust and dirt every 3-4 months and wipe the surface with water.

2.In the event of a typhoon or rainy season, pay attention to wipe the surface of the stainless steel with clean water in time to prevent the salt-containing liquid from corroding the surface of the stainless steel with dust and dirt. Similar rust phenomenon occurs.Pay special attention to the gaps not to accumulate water, such as the contact surface between the door and the door frame. 

3.If the corrosion of the stainless steel surface is caused by the usual inattention to maintenance, use a special stainless steel cleaner to clean the surface in time, remove the contaminants, and then wipe it clean with water. As long as it is kept clean and dry, it is guaranteed that there will be no more similar phenomena.However, if the corrosion time is too long and it is not cleaned, the stainless steel corrosion will turn into pitting corrosion, and the concave spots on the surface may not be restored.

4.Note that in the daily cleaning process, you can generally use clean water.Do not use detergent or other non-stainless steel special cleaning agents to clean, such as soap, washing powder, etc., and avoid using gasoline, diesel, engine oil, tinashui and other chemicals to clean the surface dirt of stainless steel.It is also impossible to use tools with carbon steel or that have been in contact with carbon steel (such as wire brushes) to clean the surface of stainless steel to avoid carbon steel being embedded in the surface of stainless steel, causing rust.

Therefore, while choosing a good product, the need for daily maintenance and maintenance of stainless steel is a necessary means to protect stainless steel.