Analysis of the causes of rust in stainless welded steel pipe

1.What is stainless welded steel pipe?

Stainless welded steel pipe is an important pipe material widely used in various industrial fields and construction projects. It has excellent corrosion resistance, high strength and good processing properties, and is regarded as one of the high-quality pipe materials. One of the main advantages of stainless welded steel pipe is its excellent corrosion resistance. Since stainless steel contains alloy elements such as chromium, it has good corrosion resistance in most corrosive media. This makes stainless steel welded pipes widely used in chemical industry, petroleum, marine engineering and other fields, and can withstand various corrosive environments stably for a long time. Stainless steel welded pipes also have important application value in construction projects. It is often used in building structures, indoor and outdoor decoration, water supply pipes, etc. Stainless welded steel pipe not only has a beautiful appearance, but also maintains long-term and stable performance, adapting to various complex usage environments and engineering needs.

2. Will stainless welded steel pipe rust?

Stainless welded steel pipe has strong corrosion resistance, but all electrochemical reactions or chemical reactions will occur on the metal surface in a corrosive environment, and stainless welded steel pipe will be uniformly corroded. Parts of the passive film on the surface of stainless steel with weak corrosion resistance will form pitting corrosion reactions due to self-excited reactions, resulting in small holes. In addition, chlorine ions will approach, forming a very corrosive solution, accelerating the rate of corrosion reactions. Therefore, the corroded stainless welded steel pipe will still rust. Not only that, the stainless welded steel pipe will also rust due to dissimilar metal adhesion, corrosion by chemical media, high temperature thermal oxidation, mechanical damage, etc. It is stainless steel. Analysis of some causes of welded pipe rust and solutions.

3. The main reasons why stainless welded steel pipe rusts are as follows:

Dissimilar metal attachment: When dissimilar metals that are easy to rust, such as iron powder, iron cuttings, etc., are attached to the surface of stainless welded steel pipes, it is easy to cause local corrosion and lead to rust.

Chemical medium corrosion: When stainless welded steel pipe comes into contact with chemical media such as acids, alkalis, and salts, if the environmental conditions are inappropriate or the medium concentration is high, chemical corrosion may occur and rust spots may occur.

High-temperature thermal oxidation: In high-temperature environments, thermal oxidation reactions may occur on the surface of stainless welded steel pipes, producing an oxide layer. When the oxide layer is damaged, the rust process will be accelerated.

Mechanical damage: When the surface of stainless welded steel pipe suffers mechanical damage or scratches, the original oxide film may be destroyed, making it susceptible to corrosion and rust.

Oxygen and moisture: In an environment where oxygen and moisture exist, stainless welded steel pipe may form scale and oxides, causing surface rust if it is not cleaned and maintained in time.

External pollutants: If industrial pollution, dust, chemicals, etc. are deposited on the surface of stainless steel welded pipes for a long time, they will affect its corrosion resistance and lead to rust.

During the welding process, carbide precipitation in stainless steel materials is a common problem, which will lead to a decrease in the corrosion resistance of stainless steel. At the same time, high temperature environments will also cause the degradation of stainless steel properties.

Surface contamination: Contact with certain metal particles, such as iron or steel from other sources, can transfer onto stainless steel surfaces.

Other Reasons Stainless Steel Rusts

Crevice corrosion: The presence of tight gaps, seams, or crevices on stainless steel surfaces can promote crevice corrosion.

Excessive heat: Stainless steel has a high melting point and is generally resistant to heat.

Welding defects: Improper welding techniques or the use of incorrect filler materials can compromise the corrosion resistance of stainless steel.

Damaging chemical exposure：Exposing stainless steel to certain chemicals can lead to corrosion and rusting. Harsh chemicals such as hydrochloric acid, sulfuric acid, and certain cleaning agents may contain corrosive ingredients that can eat away at the protective layer on stainless steel surfaces. 

Contact with saline：Exposure to saline, such as seawater or salt sprays, can be another reason why stainless steel may rust. The chloride ions present in these saltwater environments can disrupt the passive film on stainless steel, making it more prone to corrosion.

4. The following are some effective measures:

Keep the material clean: Before welding, make sure the surface of the stainless steel material is clean. To remove oil, oxides and other impurities on the surface, special cleaning agents and methods can be used, such as alcohol cleaning, solvent cleaning or mechanical grinding, to ensure that no external impurities will invade during the welding process.

Prevent the intrusion of external impurities: During the welding process, the intrusion of external impurities must be strictly controlled, especially carbon, oxygen, nitrogen and other impurities that can easily cause problems. The intrusion of external impurities can be reduced by improving the purity of the welding environment. For example, using high-purity argon as a shielding gas can ensure adequate argon shielding on the premise that the argon purity inspection passes.

Control the welding temperature: During the welding process, strictly control the welding temperature to avoid excessive temperature causing degradation of stainless steel materials and precipitation of carbides. Appropriate welding parameters and techniques can be used to control the welding speed and power to ensure that the temperature during the welding process is controlled within an appropriate range.

Choose the appropriate welding method: Different welding methods have different effects on stainless steel materials, and the appropriate welding method should be selected according to the specific situation. For example, argon arc welding is a commonly used welding method that can provide a good protective atmosphere, but attention needs to be paid to the control of argon gas purity and gas flow to ensure welding quality.

Regular inspection and maintenance of stainless welded steel pipe: Regular inspection and maintenance of welded stainless steel structures is very important, so that potential problems can be discovered and dealt with in time, extending the service life of stainless steel materials and maintaining good performance.

In general, by keeping the material clean, controlling the intrusion of external impurities, reasonably controlling the welding temperature, selecting appropriate welding methods, and conducting regular inspections and maintenance, problems such as carbonized precipitation and reduced corrosion resistance during stainless steel welding can be effectively avoided. Ensure the quality and stability of stainless steel structures.

To sum up, there are many reasons why stainless steel welded pipes rust. In addition to the characteristics of the material itself, it is also closely related to factors such as environment, usage conditions, and maintenance. Therefore, when using and maintaining stainless steel welded pipes, attention needs to be paid to avoiding the effects of the above factors in order to extend their service life and maintain good appearance and performance.