Hot-dip galvanized steel pipe

Hot-dip galvanized steel pipe is a type of steel pipe with strong corrosion resistance, which is formed by immersing ordinary steel pipes (usually carbon steel pipes) in molten zinc at about 450℃ after pickling and rust removal, so that a dense zinc layer evenly covers the surface.

What are the characteristics and performance advantages of hot-dip galvanized pipes

Corrosion resistance: The galvanized coating can effectively protect steel from various environmental factors, preventing steel pipes from rusting and corroding.
Durability: The zinc coating of hot-dip galvanized steel pipes is relatively thick, generally ranging from 35 to 85 μm, which enables them to have a long service life and the ability to withstand harsh environmental conditions.
Good mechanical properties: It can combine the strength of steel with the protection of zinc coating, making it suitable for structural applications.
Economical and practical: Hot-dip galvanized steel pipes offer a high cost-performance ratio. Although they are slightly more expensive than uncoated steel pipes, they are more durable and their overall cost is significantly lower than that of stainless steel pipes.

The main production process of hot-dip galvanized pipes

The general process flow of hot-dip galvanizing is: degreasing → pickling → flux plating → zinc immersion → cooling → passivation

Among them, degreasing and pickling are treatments carried out on the surface of steel pipes to remove oil stains and rust on the surface of the steel pipes. Degreasing usually uses solvents or alkaline solutions, while pickling uses sulfuric acid or hydrochloric acid to remove the oxide scale and rust layer on the surface of the steel pipes.

Flux plating (immersion in flux solution) : Apply a mixture of ammonium chloride and zinc chloride on the surface of the steel pipe to prevent it from oxidizing again before heating.

Zinc immersion: The steel pipe is immersed in molten zinc liquid for usually tens of seconds or several minutes.

Cooling: Allow the steel pipe to cool naturally or with water to solidify the coating.

Passivation: Enhance the corrosion resistance of the galvanized layer and prevent the appearance of "white rust".

What is the anti-corrosion principle of hot-dip galvanized pipes?

The anti-corrosion principle of hot-dip galvanized pipes mainly comes from its multiple protection mechanisms: physical isolation + electrochemical protection + passivation film

Physical isolation: During hot-dip galvanizing, the surface of the steel pipe is covered with a dense zinc layer. This zinc layer can effectively isolate the steel from air, moisture, oxygen and corrosive media, avoiding direct contact between the steel and the outside world.
Electrochemical protection: Zinc is more active than iron. In electrochemical corrosion, zinc acts as a "sacrificial anode" and undergoes oxidation reactions first. When the zinc coating is scratched or damaged and the steel is exposed, the surrounding zinc will dissolve first to protect the steel from corrosion.
Passivation and protective film formation: In the air, a layer of zinc oxide and zinc hydroxide rapidly forms on the surface of the zinc layer, which further reacts with carbon dioxide in the air to form a dense basic zinc carbonate, significantly enhancing the anti-corrosion performance.

Technical standards (some common standards)

China: GB/T 3091 (Welded Galvanized steel pipes for Low-pressure fluid Conveyance), GB/T 13793
United States: ASTM A53, ASTM A123, ASTM A795
Europe: EN 10240, EN 39 (for scaffolding)
Japan: JIS G3444

Other common galvanizing methods

In addition to hot-dip galvanizing, there are many different galvanizing methods, and the processes and coating properties of different methods vary greatly:

Electro-galvanizing: Through electrolytic action, a relatively thin layer of zinc is deposited on the surface of the steel pipe. The coating applied by this method is uniform and suitable for small parts with strict dimensional requirements.
Mechanical galvanizing: Steel parts are rubbed and collided with zinc powder, glass beads, etc. in a drum to evenly cover the surface of the steel with zinc powder. The feature is that it does not require high-temperature treatment and is suitable for small parts, bolts, nuts and other fasteners.
Hot-dip galvanizing: Zinc wire or zinc powder is melted and then sprayed at high speed onto the surface of steel to form a zinc coating. The zinc coating applied by this method has a relatively good bonding force, but it has higher requirements for equipment and will incur additional costs.

Hot-dip galvanized steel pipes are widely used in:

Construction engineering: scaffolding, steel structure supports, curtain wall keels.
Water supply and drainage system: low-pressure fluid transportation, water pipes, heating pipes.
Electric power communication: Cable protection conduit.
Agricultural facilities: greenhouses, agricultural pipelines.
Traffic facilities: Road guardrails, bridge components.
Mechanical manufacturing: Conveying pipelines, protective structural components.

Summary

Hot-dip galvanized steel pipes (hot-dip galvanized steel pipes) have become common materials in construction, piping and infrastructure projects due to their high cost performance, excellent corrosion resistance and wide application range. It combines strength and protective performance, and is an economical solution between carbon steel pipes and stainless steel pipes.