1.What are the manifestations and causes of local rust caused by damage to the galvanized layer?
Symptoms: Rust spots and rust stains appear on the surface, mostly at scratches, collision depressions or cutting/welding incisions.
Causes: The galvanized layer is mechanically damaged during transportation and installation, exposing the metal substrate.
The high temperature of welding destroys the galvanized layer around the weld, forming electrochemical corrosion conditions.
Friction (such as contact with sharp objects) causes the galvanized layer to gradually wear away.
2.What are the manifestations and causes of comprehensive corrosion caused by aging and shedding of the zinc coating?
Manifestations: The zinc coating peels and flakes off over a large area, and the substrate is exposed and rusted in pieces.
Causes: The zinc coating is slowly corroded due to long-term exposure to strong acid, strong alkali or high salt spray environments (such as chemical plants and coastal areas).
High temperature environments (such as near heat sources) accelerate the oxidation of the zinc coating, causing the coating to become brittle and fall off.
Defects in the zinc coating process (such as insufficient coating thickness and poor adhesion) shorten the service life.
3.What are the manifestations and causes of crevice corrosion and electrochemical corrosion?
Symptoms: Rust inside the bolt joints and pipe joints, and even rusty water seeping out.
Causes: Water and dust easily accumulate in the gaps, forming a humid environment, causing electrochemical corrosion (zinc and iron form a primary battery).
Contact between different metals (such as galvanized square tubes connected to stainless steel parts) accelerates corrosion due to potential difference.
4.What are the manifestations and causes of accelerated corrosion caused by environmental factors?
Symptoms: "White rust" (zinc oxide or hydroxide) appears on the surface of the square tube in open air or humid environment, and develops into red rust (iron oxide) in severe cases.
Causes: Long-term rain or high air humidity causes electrochemical reaction of the zinc coating (zinc reacts with water and oxygen).
Contact with industrial waste gas (such as sulfur compounds) or acid mist, which reacts chemically with the zinc coating.
5.What are the daily management measures to prevent corrosion?
1. Environmental control
Avoid storing with acidic or alkaline substances (such as sulfuric acid and caustic soda) and keep the warehouse ventilated and dry.
When stacking in the open air, cover with waterproof cloth and raise the bottom by more than 30cm to prevent erosion by ground water.
2. Regular inspection system
Establish corrosion inspection files, record the corrosion conditions of each part, and focus on marking the corrosion-prone areas (such as welds, cuts, and bottoms).
Use a thickness gauge to detect the wall thickness of the square tube every year. If the wall thickness thinning rate is found to be accelerated (such as more than 0.1mm per year), analyze the reasons and strengthen protection.
3. Personnel operation specifications
Avoid violent impact during installation and transportation, and use special lifting equipment (such as nylon slings) to prevent scratches on the galvanized layer.
It is prohibited to directly weld other metals on the surface of the square tube (if welding is necessary, post-weld anti-corrosion should be done in advance).