What is the corrosion resistance of large cross-section multi-channel folding pipes
Information summary：The corrosion resistance of large cross-section multi-channel folding pipes depends on the substrate material, surface treatment process, as well as the stress and gap effects caused by the folding structure. Its corrosion resistance performance needs to be comprehensively judged based on material and structural characteristics. The specific analysis is as follows:
The corrosion resistance of large cross-section multi-channel folding pipes depends on the substrate material, surface treatment process, as well as the stress and gap effects caused by the folding structure. Its corrosion resistance performance needs to be comprehensively judged based on material and structural characteristics. The specific analysis is as follows:
1、 The substrate material is the core determinant of corrosion resistance
The corrosion resistance of different substrates varies significantly, and the adaptation scenarios are also different:
1. Plastic substrates (PE, PP, PVC, PTFE)
PE/PP material: resistant to acid, alkali, salt solution and other chemical media corrosion, suitable for chemical fluid transportation, municipal sewage discharge and other scenarios. It has good resistance to non oxidizing acids (hydrochloric acid, dilute sulfuric acid), but is not resistant to strong oxidants (concentrated nitric acid, chromic acid). Under the design of large cross-section and multiple channels, the chemical stability of plastic material is not affected by its structure, and its corrosion resistance is stable.
PVC material: better corrosion resistance than PE/PP, lower cost, but high low-temperature brittleness, suitable for transporting corrosive fluids at room temperature.
PTFE (polytetrafluoroethylene) material: It has extremely strong corrosion resistance and can withstand almost all strong acids, alkalis, and organic solvents. It is known as the "plastic king" and is suitable for strong corrosion scenarios such as chemical and pharmaceutical industries. However, it is expensive and difficult to process.
2. Metal substrates (stainless steel, aluminum alloy, titanium alloy)
304 stainless steel: resistant to atmospheric, freshwater, and weakly corrosive media, suitable for ordinary industrial scenarios, but prone to pitting corrosion in chloride ion environments (seawater, saltwater).
316/316L stainless steel: Adding molybdenum element greatly improves its resistance to chloride ion corrosion, making it suitable for strong corrosive environments such as marine and chemical industries. The 316L low-carbon version is more resistant to intergranular corrosion.
Titanium alloy: Corrosion resistance close to PTFE, resistant to seawater, strong acids, and strong alkalis, suitable for aerospace, marine engineering, and other fields, but at a higher cost.
Aluminum alloy: easy to form dense oxide film on the surface, resistant to atmospheric corrosion, but not resistant to acid, alkali, and salt spray, mostly used in light load and low corrosion scenarios.
2、 The impact of folding structure on corrosion resistance (key risk points)
The folding design of large cross-section and multiple channels will bring about two major problems: stress corrosion and crevice corrosion, which directly affect the overall corrosion resistance performance:
1. Stress corrosion risk
During the forming process, residual stress will be generated at the bending point of the folding tube; If subjected to fluid pressure or external loads during use, stress will further concentrate. Under the combined action of corrosive media (such as chloride ions and acid solutions) and stress, stress corrosion cracking (SCC) is prone to occur at the bending point, especially in metal folding pipes, which is the most common form of failure.
Optimization plan: Annealing the metal folding tube to eliminate residual stress; Choose materials with good toughness (such as HDPE) for plastic folding pipes to reduce bending stress.
2. Gap corrosion risk
The separation of multiple channels and the gaps between folded layers can easily accumulate media, impurities, and moisture, forming a closed battery and causing local corrosion. For example, if seawater accumulates in the gaps of stainless steel folding pipes, the metal inside the gaps will accelerate corrosion due to the difference in oxygen concentration, gradually penetrating the pipe wall.
Optimization plan: Adopt seamless integrated molding technology instead of splicing and folding; Fill the gaps with corrosion-resistant sealant (such as fluororubber); Choose materials with strong self passivation ability (such as 316L stainless steel, titanium alloy).
3、 The strengthening effect of surface treatment process on corrosion resistance
Surface treatment can significantly improve the corrosion resistance of folding tubes, especially suitable for metal substrates:
1. Metal surface treatment
Hot dip galvanizing/electroplating galvanizing: forms a zinc layer on the surface of carbon steel substrate, sacrifices anode protection substrate, suitable for outdoor low corrosion scenarios, but the zinc layer is easily damaged by strong acids and alkalis.
Spray anti-corrosion coating: such as epoxy resin, polyurethane, fluorocarbon coating, which isolates the substrate from contact with corrosive media. When the coating thickness is ≥ 150 μ m, the corrosion resistance is greatly improved, making it suitable for chemical and marine scenes.
Passivation treatment: After passivation solution treatment, a dense oxide film is formed on the surface of stainless steel, enhancing its resistance to pitting corrosion and intergranular corrosion.
2. Plastic surface treatment
Plasma modification: enhances the adhesion of plastic surfaces, facilitating the subsequent application of functional coatings;
UV resistant coating: prevents plastic folding pipes used outdoors from reducing their corrosion resistance due to UV aging.
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