Surface Treatment Technology of SS Welded Pipes

Jane

Stainless steel welded pipe is a steel pipe made by welding common steel or steel strip after curling and forming through a unit and a mold. Because its production process is relatively simple, its production efficiency is high and it can quickly meet the market demand for different specifications, which makes its varieties and specifications very rich. In addition, its equipment investment is small, and the production cost is also reduced, which is very competitive in the market.

The connection and difference between ss welded pipe and ss seamless pipe

The connection:

1. Same materials: Both are made of stainless steel (such as 304, 316L), which has the characteristics of corrosion resistance and high temperature resistance.
2. Cross-process: Both can improve the surface performance through polishing, pickling and other treatments, and some application scenarios (such as low-pressure pipelines) can be replaced by each other.

The difference:

1. Manufacturing process:

Welded pipe: Steel plate/strip is curled and welded, with welds, suitable for large diameter (such as above DN1000) and thin-walled pipes;

Seamless pipe: Round steel is perforated and hot-rolled or cold-drawn, without welds, and is homogeneous overall.

2. Performance differences:

Welded pipes have weak pressure bearing capacity because the weld may become a weak point (post-weld treatment such as flaw detection and grinding is required);

Seamless pipes have high strength, are resistant to high pressure and high temperature, and are suitable for harsh working conditions (such as chemical equipment and boilers).

3. Cost and use:

Welded pipes have low costs and are mostly used for decoration and low-pressure fluid transportation;

Seamless pipes have high costs and are used exclusively in high-demand industrial fields.

Importance of surface treatment of ss welded pipe

Although stainless steel welded pipes themselves have certain corrosion resistance and aesthetics, surface treatment is particularly critical in order to fully exert their performance advantages in different scenarios, which can be called the “beauty secret” of welded pipes.

From the perspective of corrosion resistance, the oxide film on the surface of the stainless steel welded pipe may be destroyed during the production and processing process. For example, high temperature during welding will accelerate the oxidation of the weld and surrounding areas, reducing local corrosion resistance. Proper surface treatment can repair and strengthen this protective film. For example, in coastal buildings and chemical environments, surface-treated welded pipes can effectively resist erosion by sea breeze and chemicals, greatly extending their service life.

In terms of aesthetics, the surface of untreated welded pipes may have defects, uneven color and other problems. Through surface treatment, the surface of the welded pipe can become smooth and bright, or create a unique texture such as frosted or brushed. When used in the decoration field, it can enhance the refinement and fashion sense of the overall space.

In terms of welding reliability, a clean and flat surface can make the welding more solid, reduce defects such as pores and cracks, and ensure that when the welded pipe is under pressure and tension, problems will not easily occur at the welding part. This is of great significance in load-bearing structures such as buildings and bridges. When subsequent processing such as coating and painting is required on the surface of the welded pipe, good surface treatment can ensure that the coating has stronger adhesion and is not easy to fall off or peel off. While maintaining the appearance, it further enhances the protective performance.

Common surface treatment processes

1. Mechanical grinding: Mechanical grinding is the basic process for surface treatment of stainless steel welded pipes. It usually uses equipment such as belt sanders and grinding wheels to remove surface oxide films, stains and minor flaws by friction between the grinding tools and the surface of the welded pipe.
2. Pickling and polishing: Pickling and polishing uses the chemical reaction between acid and the surface of stainless steel to remove oxide film, rust and other contaminants. Common acids include nitric acid, hydrofluoric acid, etc. They can quickly dissolve metal oxides and reveal a pure metallic luster on the surface of the welded pipe.
3. Electrochemical polishing: Electrochemical polishing is to selectively dissolve the stainless steel welded pipe as the anode in a specific electrolyte by applying a DC power supply. The raised part of the anode surface has a large current density and a fast dissolution rate, while the concave part dissolves slowly, so that the surface is gradually flat and smooth to achieve the purpose of polishing.

Other special processing methods

In addition to the above common methods, there is also original surface treatment, that is, the surface that has been heat treated and pickled after hot rolling, which is mostly used for cold rolled materials, industrial tanks, etc. After blunt surface treatment, heat treatment and pickling after cold rolling, the material is soft and has a silvery white luster, suitable for deep stamping processing, such as automotive components; Matt surface treatment, fine rolling processing on the basis of dull surface, makes the surface moderately bright and easy to re-grind, commonly used in tableware and building materials; Fine sand treatment, grinding with 150-180 grinding belt, with better gloss and discontinuous coarse grain, used for baths, building decoration, etc.

Choose according to your needs to achieve the best

Different surface treatment processes for stainless steel welded pipes have their own advantages. Mechanical grinding is easy to operate and low cost, but the surface accuracy is limited; Pickling and polishing can effectively remove impurities, improve corrosion resistance and finish, but it requires high acid control; Electrochemical polishing can achieve high-precision polishing, but is restricted by equipment and process parameters. The original surface treatment keeps the original state and is used in specific industrial scenes; Blunt surface, matte surface, fine sand, #320 treatment, hairy surface treatment, bright surface treatment have their own unique surface textures to meet different decoration and industrial needs.

In practical applications, accurate selection is required based on the usage scenario and needs. In building structures, mechanically polished welded pipes can meet basic strength and corrosion resistance requirements, and the cost is controllable; in the food and medical industries, pickled and polished welded pipes can ensure hygiene and safety; in precision instruments, electrochemically polished welded pipes can ensure high precision and perfect appearance. Only by choosing the right surface treatment process can the performance of stainless steel welded pipes be fully utilized.

Read more: How to Care and Maintain Stainless Steel Welded Pipes?