Key Takeaways
"Cold galvanized pipe" means electro-galvanized pipe: a thin zinc coating deposited electrolytically on the pipe surface.
Electro-galvanized coatings are thin (commonly in the tens of g/m² range) and adhere far less well than hot-dip coatings; corrosion resistance is correspondingly poor.
In China, cold-galvanized pipe has been officially eliminated for water and gas supply service, and is not allowed in new residential potable-water lines.
For water, gas and structural service, specify hot-dip galvanized pipe to the applicable standard (for example GB/T 3091 or the equivalent national standard) instead.
1. What "Cold Galvanized" Means
The term "cold galvanized" is used in the trade for electro-galvanized pipe: the pipe is coated by electrodeposition of zinc rather than by immersion in molten zinc. The process deposits a thin zinc layer - typically in the tens of g/m² range depending on the process and standard used (for example electro-galvanized flat products under GB/T 15675 or EN 10152 use different coating classes) - compared with hot-dip coatings that are commonly several times heavier. Because the coating is thin and the bond between zinc and steel is mechanical in nature, the layer chips, scratches and corrodes much more readily than a hot-dip coating.
2. Cold Galvanized vs Hot-Dip: Key Differences
| Aspect | Cold galvanized (electro) | Hot-dip galvanized |
|---|---|---|
| Process | Electrolytic zinc deposition | Immersion in molten zinc |
| Coating weight | Thin, typically tens of g/m² | Heavier, typically several times thicker (per GB/T 3091 or ISO 1461 classes) |
| Adhesion | Weak, prone to chipping | Metallurgical bond, durable |
| Corrosion resistance | Poor in wet or buried service | Good, proven in water and structural service |
| Typical use | Indoor, dry, lightly protected parts | Water, gas, fencing, structural and outdoor service |
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3. Why Cold-Galvanized Pipe Is Not for Water or Gas
Chinese construction authorities have formally eliminated backward cold-galvanized pipe technology from water and gas supply applications, and the use of cold-galvanized pipe as a potable-water line in new residential buildings is prohibited. The reasons are technical: the thin zinc layer cannot provide the decades-long protection that hot-dip coatings give, zinc loss exposes bare steel quickly, and the coating is easily damaged during installation. If a project calls for galvanized pipe for water supply, specify hot-dip galvanized pipe to the current standard and confirm the coating class with the supplier.
4. When Electro-Galvanized Pipe Can Still Be Used
Electro-galvanized tube is acceptable in dry indoor applications where light protection is enough - for example furniture frames, cable trays and some equipment structures - provided the environment is not wet, condensing or chemically aggressive. For buried, outdoor, water or gas service, use hot-dip galvanized or appropriate coated pipe.
Packaging and Transportation of Galvanized Pipes
Frequently Asked Questions
Q1. What is the coating weight of cold galvanized pipe?
Electro-galvanized coatings are thin, typically in the tens of g/m² range, far below hot-dip classes. Confirm the exact class per the applicable standard and COA.
Q2. Can cold galvanized pipe be used for drinking water?
No. Cold-galvanized pipe is not accepted for potable-water supply in new residential buildings; use hot-dip galvanized pipe to the applicable standard.
Q3. Is electro-galvanizing the same as galvanizing?
No. "Galvanizing" in the pipe trade normally means hot-dip galvanizing with a thick metallurgically bonded coating; electro-galvanizing is a different, thinner process.