What are the surface treatment and processing methods for thick-walled steel pipes

Thick-walled steel pipes come in a wide variety of steel grades and specifications, with diverse performance requirements. All of these should be differentiated according to changes in user requirements or working conditions. Generally, steel pipe products are classified according to cross-sectional shape, production method, pipe material, connection method, coating characteristics, and application. Thick-walled steel pipes can be divided into round steel pipes and shaped steel pipes according to their cross-sectional shape.

Shaped thick-walled steel pipes refer to steel pipes with various non-circular cross-sections, including: square pipes, rectangular pipes, elliptical pipes, flat elliptical pipes, semi-circular pipes, hexagonal pipes, hexagonal inner round pipes, unequal-sided hexagonal pipes, equilateral triangular pipes, pentagonal plum blossom pipes, octagonal pipes, convex-shaped pipes, and double-convex pipes. Thick-walled steel pipes include double-concave pipes, multi-concave pipes, seed-shaped pipes, flat pipes, rhomboid pipes, star-shaped pipes, parallelogram-shaped pipes, ribbed pipes, teardrop-shaped pipes, internally finned pipes, twisted pipes, type B pipes, type D pipes, and multi-layer pipes.

Thick-walled steel pipes are further classified according to their longitudinal cross-sectional shape into constant cross-section steel pipes and variable cross-section steel pipes. Variable cross-section (or variable section) steel pipes refer to steel pipes whose cross-sectional shape, inner and outer diameters, and wall thickness change periodically or non-periodically along the pipe's length. These mainly include: externally tapered pipes, internally tapered pipes, externally stepped pipes, internally stepped pipes, periodically cross-section pipes, corrugated pipes, spiral pipes, steel pipes with heat dissipation fins, and gun barrels with double-lined sections.

To improve the service life of oil and gas pipelines, surface treatment is usually performed to facilitate a strong bond between the thick-walled steel pipe and the anti-corrosion layer. Common treatment methods include: cleaning, tool rust removal, pickling, and shot blasting.

1. Surface Pickling of Thick-Walled Steel Pipes: Common pickling methods include chemical and electrolytic pickling. However, only chemical pickling is used for pipeline corrosion protection. Chemical pickling achieves the desired cleanliness and roughness on the surface of thick-walled steel pipes, facilitating subsequent anchoring of patterns. It is usually used as a post-treatment after shot blasting (sandblasting).

2. Shot Blasting for Rust Removal: A high-powered motor drives blades to rotate at high speed, causing abrasives such as steel grit, steel shot, wire segments, and minerals to be blasted onto the surface of the thick-walled steel pipe under centrifugal force. This removes rust, oxygen reactants, and dirt, while the intense impact and friction of the abrasives achieve the required uniform roughness.

3. Cleaning of Thick-Walled Steel Pipes: Grease, dust, lubricants, and organic matter adhering to the surface of thick-walled steel pipes are usually cleaned using solvents and emulsions. However, rust, oxygen reactants, and welding slag on the surface of thick-walled steel pipes cannot be removed and require further treatment methods.

4. Rust Removal Using Tools for Thick-Walled Steel Pipes

Oxygen scale, rust, and welding slag on the surface of thick-walled steel pipes can be cleaned and polished using a wire brush. Rust removal using tools is divided into manual and power-operated methods. Manual tool rust removal can achieve Sa2 grade, while power tool rust removal can achieve Sa3 grade. If the surface of thick-walled steel pipes has particularly strong oxygen scale, it may not be completely removed even with tools, requiring alternative methods.

Of the four surface treatment methods for thick-walled steel pipes, shot blasting is the ideal method. Generally, shot blasting is mainly used for the inner surface treatment of thick-walled steel pipes, while shot blasting is mainly used for the outer surface treatment.

The main processing method for thick-walled steel pipes is rolling. This is a pressure processing method where steel billets are passed through the gap between a pair of rotating rollers (of various shapes). Due to the compression of the rollers, the cross-section of the material decreases, increasing the length of the thick-walled steel pipe. This is a common production method for steel products, mainly used to produce steel profiles, plates, and pipes. It is divided into cold rolling and hot rolling. Forged steel: A pressure processing method that uses the reciprocating impact force of a forging hammer or the pressure of a press to change a billet into the desired shape and size. It is generally divided into free forging and die forging. Seamless steel pipes remain an indispensable material for various conventional weapons; gun barrels, cannon barrels, etc., are all made from steel pipes. Steel pipes can be divided into round pipes and shaped pipes according to the shape of their cross-sectional area. Because, given the same perimeter, a circle has a large area, a round pipe can transport more fluid.

Furthermore, the circular cross-section of thick-walled steel pipes experiences more even stress when subjected to internal or external radial pressure; therefore, the vast majority of thick-walled steel pipes are round. Steel pipes have a hollow cross-section and are widely used as pipelines for transporting fluids, such as oil, natural gas, coal gas, water, and certain solid materials. Compared with solid steel materials such as round steel, seamless steel pipes are lighter in weight while maintaining the same bending and torsional strength. Thick-walled steel pipes are an economical cross-section steel material, widely used in the manufacture of structural components and mechanical parts, such as oil drill pipes, automobile drive shafts, bicycle frames, and steel scaffolding used in construction.