Common Anti-corrosion Treatment Techniques
Coating Anti-corrosion
This is a relatively common method. Common coating materials include epoxy resin and polyethylene. Taking epoxy resin coating as an example, it can form a dense protective film on the surface of steel bellows, effectively isolating water, oxygen and corrosive media from contact with steel. Moreover, the epoxy resin coating has strong adhesion, can remain stable for a long time, and is not easy to fall off, providing reliable protection for the steel corrugated pipe.

Galvanizing Anti-corrosion: A layer of zinc is applied to the surface of the steel corrugated pipe by hot-dip galvanizing or electro-galvanizing. Zinc is more chemically active than iron. In a corrosive environment, zinc will corrode first, thus protecting the steel. The hot-dip galvanized zinc layer is thicker and has a better anti-corrosion effect. It is suitable for some occasions with high anti-corrosion requirements, such as underground drainage pipes.

Cathodic protection is an electrochemical protection method that applies an electric current to the steel bellows, making it the cathode and thus inhibiting the corrosion of the steel. The sacrificial anode method is usually used to connect metals that are more active than steel (such as magnesium, zinc, etc.) to the steel bellows. The active metal acts as the anode and continuously dissolves, protecting the steel bellows as the cathode.

The differences between cold-rolled and hot-rolled rebar lie primarily in processing technology, material properties, and application scenarios.
Cold rolling is carried out at room temperature, while hot rolling requires high-temperature heating. This temperature difference leads to significant differences in hardness, toughness, surface quality, etc. between the two.

The temperature of the cold rolling process is usually controlled at room temperature. The steel billet is deformed through mechanical pressure and directly rolled into rebar. Due to the low temperature, the grains inside the steel are crushed, the structure is denser, and the material has higher hardness and strength. Cold-rolled rebar has a smooth surface, high dimensional accuracy, and the error can be controlled at the millimeter level. It is suitable for scenarios with strict requirements on surface flatness, such as precision mechanical parts and decorative building materials. However, the cold rolling process will make the steel brittle, reduce its impact toughness, and make it prone to cracking when bent, so annealing treatment is required before processing.

Hot rolling requires heating the steel billet to above 1100℃. The high temperature softens the steel and makes it easier to shape during rolling. After rolling, the rebar cools naturally and the internal grains are rearranged to form a coarse and uniform structure with better toughness than cold-rolled steel. The surface of hot-rolled rebar has oxide scale, slight bumps and color differences, and the dimensional error is usually more than 5 mm, but it has good impact resistance and can withstand repeated bending. Hot-rolled products are commonly used in beam and column steel bars and bridge supports at construction sites, and their cost is about 30% lower than that of cold-rolled products.

In terms of material properties, the yield strength of cold-rolled rebar can reach over 500MPa, which is about 20% higher than that of hot-rolled, but the elongation is only two-thirds of that of hot-rolled products. If both are immersed in salt water for corrosion testing, cold-rolled steel rusts 40% slower than hot-rolled steel due to the protection of the dense oxide layer on the surface. Things to note during construction: arc welding is required for cold-rolled rebar welding, as ordinary arc welding is prone to burn-through; the oxide scale must be removed before welding hot-rolled rebar, otherwise the weld strength will be reduced by 15%.

The choice between cold-rolling and hot-rolling depends on specific needs.

The precision rolled seamless steel pipe is made by hot rolling or cold rolling and other precision processing technologies. After the solid steel billet is pierced, it goes through multiple rolling and finishing processes to make the pipe wall uniform, with high dimensional accuracy and good surface finish.
Ordinary steel pipes are usually produced by welding or simple extrusion molding. The production process is relatively simple, and the precision and surface quality are not as good as those of precision-rolled seamless steel pipes.

The precision rolled seamless steel pipe has excellent mechanical properties, such as high strength, high toughness, good fatigue resistance and high pressure resistance. This is because its internal structure is uniform, without defects such as welds, and it can better withstand various stresses and working conditions. The production process of the finished rolled tube can produce dimensional equipment and high-precision dimensions below 0.1 mm. The finished rolled tube has a smooth surface and high dimensional accuracy.
Due to the presence of welds, the mechanical properties of ordinary steel pipes are relatively poor, especially when subjected to high pressure, high temperature, or alternating loads; they are prone to problems such as cracks and leakage. Ordinary rolled tube products may have large dimensional errors.