Hot-dip galvanized pipe vs cold-dip galvanized pipe: process differences and performance comparison

Hot-dip galvanized pipes and cold-dip galvanized pipes are common metal anti-corrosion treatment methods. There are significant differences between the two in terms of process, performance and application scenarios. The following is a detailed comparison from the aspects of process principle, performance and applicable scenarios.

1. Differences in process principle
Hot-dip galvanized pipe
Process flow: The steel is immersed in molten zinc liquid at 450℃~480℃, and a zinc-iron alloy layer is formed on the surface of the steel through chemical reaction.
Coating structure: From the outside to the inside, there is a pure zinc layer, a zinc-iron alloy layer and a substrate, and the coating is tightly combined with the substrate.
Coverage: A uniform coating can be formed on the inner and outer walls of the pipe, which is suitable for full anti-corrosion needs.
Cold-dip galvanized pipe (electrogalvanized)
Process flow: Using the principle of electrolysis, the steel is immersed in an electrolyte containing zinc ions at room temperature, and the zinc ions are deposited on the surface of the steel through the action of electric current.
Coating structure: It is only a physically attached zinc layer, without a zinc-iron alloy layer, and the bonding force with the substrate is weak.
Coverage: Usually only the outer wall of the pipe is galvanized, and the inner wall cannot be effectively covered.
2. Performance comparison analysis
Anti-corrosion performance
Hot-dip galvanized pipe: The coating thickness can reach 30μm~85μm, the zinc-iron alloy layer effectively blocks the corrosive medium, and the corrosion resistance is dozens of times that of cold galvanizing, which is suitable for harsh environments such as humidity, acid and alkali.
Cold-dip galvanized pipe: The coating thickness is only 5μm~15μm, the zinc layer is easy to fall off, the corrosion resistance is poor, and the service life is short.
Adhesion and durability
Hot-dip galvanized pipe: The zinc-iron alloy layer forms a metallurgical bond with the substrate, with strong adhesion, the coating is not easy to peel off, and the durability is high.
Cold-dip galvanized pipe: The zinc layer is physically attached, with weak adhesion, and it is easy to fall off due to friction or environmental factors.
Appearance and surface quality
Hot-dip galvanized pipe: The surface is silvery white and slightly rough. There may be zinc flowers or process water marks, but it does not affect the anti-corrosion performance.
Cold-dip galvanized pipe: smooth surface, adjustable color (such as yellow-green, bluish-white), more beautiful appearance, but poor anti-corrosion performance.
Processing and cost
Hot-dip galvanized pipe: complex process, high temperature treatment is required, large equipment investment, but the unit cost decreases with the increase of output, suitable for large-scale production.
Cold-dip galvanized pipe: simple process, low equipment cost, but thin coating, poor durability, long-term use cost may be higher.
3. Application scenario selection
Applicable scenarios for hot-dip galvanized pipe
Building structure: such as steel structure bridges, building exterior wall brackets, etc., need to be exposed to outdoor environment for a long time.
Infrastructure: highway guardrails, power towers, communication base stations, etc., require high corrosion resistance.
Industrial pipelines: gas pipelines, water supply and drainage pipelines, etc., need to withstand internal medium corrosion and external environmental influences.
Applicable scenarios for cold-dip galvanized pipes
Indoor decoration: such as furniture accessories, indoor railings, etc., with high requirements for appearance and low corrosion risk.
Temporary structures: exhibition stands and temporary fences used for a short period of time, which do not require high durability.
Small parts processing: small fasteners, hardware accessories, etc., require low-cost and fast anti-corrosion treatment.
4. Summary and suggestions
Choose hot-dip galvanized pipes:
Scenarios that require long-term anti-corrosion protection (such as outdoor, humid environment).
Projects with high requirements for structural safety (such as bridges, pipelines).
Choose cold-dip galvanized pipes:
Scenarios that only require short-term anti-corrosion or indoor use.
Small projects with high requirements for appearance and cost sensitivity.
Note: Cold-dip galvanized pipes are strictly prohibited from being used in gas pipelines, water supply and drainage pipelines and other areas involving public safety due to their poor corrosion resistance. When choosing, you should weigh the anti-corrosion performance, cost and service life according to actual needs.