Galvanized ERW pipe, GI ERW pipe

What is galvanized ERW pipe?

Galvanized ERW pipe (GI ERW Pipe) is a welded steel pipe that is coated with a layer of zinc on the surface of the steel pipe through hot-dip galvanizing (HDG) or electro-galvanizing (EG) process on the basis of high-frequency resistance welded pipe (ERW Pipe) to improve its corrosion resistance and service life. Among them, hot-dip galvanizing is more common, with thicker coating and stronger anti-rust ability.

Manufacturing process of galvanized ERW pipe:

1. ERW pipe production
The high-frequency resistance welding (Electric Resistance Welding) process is used to continuously form and weld steel strips (coils) into steel pipes.

The ERW pipe production process has the characteristics of high efficiency, low cost and high weld strength.

2. Galvanizing treatment
Hot-dip galvanizing (HDG): Place the ERW pipe (black pipe) in a molten zinc tank for hot-dip galvanizing treatment and immerse it in molten zinc liquid (about 450°C) to form a thicker zinc layer (usually 50-150μm), which has strong anti-rust ability and is suitable for outdoor environments.

Electro galvanizing (EG): Galvanizing by electrolysis, the zinc layer is thinner (5-20μm), the surface is smoother, but the anti-rust ability is weaker, and it is mostly used for indoor or short-term protection.

It should be noted that a too thin galvanized layer may not provide sufficient anti-corrosion protection, while a too thick layer may increase the internal stress of the coating, which is prone to peeling and cracking. Therefore, in actual operation, it is necessary to comprehensively consider the anti-corrosion requirements and process costs, and select the appropriate galvanized layer thickness.

Features of galvanized ERW pipe:

1. Strong corrosion resistance: The zinc layer isolates air and moisture, prevents the steel pipe from rusting, and prolongs the service life (hot-dip galvanized pipes can be used outdoors for 20-50 years).
2. Lower cost: Compared with seamless pipes and stainless steel pipes, galvanized ERW pipes are more economical and suitable for large-scale applications.
3. High strength: ERW steel pipes have high mechanical strength and still maintain good pressure bearing capacity after galvanizing.
4. Easy to process: can be cut, bent, welded (zinc supplementation is required), and construction is convenient.
5. Beautiful: The galvanized layer is silvery white and has a smooth surface, which is suitable for exposed use (such as guardrails, building frames).

Common specifications of galvanized ERW pipes:

Outer diameter range: DN15 (1/2") ~ DN600 (24")
Wall thickness range: 0.8mm ~ 10mm
Material: Q195, Q235, Q345, SPCC, ST37 and other low carbon steel

Galvanizing layer thickness (hot-dip galvanizing):
Ordinary grade ≥45μm
Thickened grade ≥80μm

Hot-dip galvanized ERW pipe vs. Electro-galvanized ERW pipe:

The difference between electro-galvanizing and hot-dip galvanizing lies in the coating thickness, corrosion resistance, cost difference, physical properties and application range. The following is a detailed introduction:

(1) Coating thickness
The coating thickness of hot-dip galvanizing is larger, usually 50 to 60 microns, or even up to 600 microns; while the coating thickness of electro-galvanizing is thinner, usually 5 to 15 microns.

(2) Corrosion resistance
The zinc layer of hot-dip galvanizing is denser and less susceptible to corrosion by oxides and salts in the environment, so it has stronger corrosion resistance; while the electro-galvanized coating is thinner and more susceptible to mechanical wear and oxide corrosion.

(3) Cost difference
The zinc layer of hot-dip galvanizing is thicker, more durable, and relatively more expensive, but has a longer service life and is more economical; the zinc layer of electro-galvanizing is thinner, the price is relatively lower, but the service life is shorter.

(4) Physical properties
The surface of hot-dip galvanized ERW steel pipe is rough, the zinc layer is thick, there are zinc flowers, and the appearance is bright; the surface of electro-galvanized ERW steel pipe is smooth and the zinc layer is thin.

(5) Application range
Hot-dip galvanized ERW steel pipe is suitable for steel structures, automobiles, agricultural machinery, construction, ships, etc., especially in harsh environments; electro-galvanizing is mostly used for small precision products and performs well in mild environments.

Application fields of galvanized ERW pipes:

Galvanized ERW pipes are widely used in various industrial and civil fields, such as water, gas, oil pipelines, building structures, agricultural irrigation systems, etc. due to their excellent anti-corrosion performance and low cost. Especially in high-pressure and low-pressure transmission systems such as oil and natural gas, ERW steel pipes are favored for their high production efficiency and low cost.

1. Construction industry: scaffolding, steel structure, door and window frames, guardrails, roof drain pipes.
2. Municipal engineering: water supply pipelines, fire protection pipelines, low-pressure gas transmission.
3. Agriculture: greenhouse brackets, irrigation systems.
4. Power communication: wire casing, cable protection tube (such as KBG/JDG tube).
5. Automobile manufacturing: some chassis parts, exhaust pipes (partially using galvanized pipes).
6. Furniture industry: shelves, table and chair brackets.

Conclusion:
Galvanized ERW pipe combines the efficient production of ERW welded pipe and the anti-corrosion performance of the galvanized layer, and is widely used in construction, municipal administration, agriculture and other fields. Hot-dip galvanized ERW pipe is more suitable for outdoor or corrosive environments, while electro-galvanized ERW pipe is suitable for indoor or short-term protection needs. When choosing, it is necessary to select reasonably according to the use environment, budget and life requirements.

Extended information:

Common types of galvanized welded pipes:

1. Hot-dip galvanized welded pipe (HDG Welded Pipe)
Galvanized by immersion in molten zinc liquid, the zinc layer is thicker (usually ≥50μm), with strong corrosion resistance, suitable for outdoor or harsh environments.
Common specifications: DN15-DN600 (1/2"-24"), wall thickness 0.8mm-10mm.

2. Electro-galvanized welded pipe (EG Welded Pipe)
Galvanized by electrolysis, the zinc layer is thinner (usually 5-20μm), the appearance is smoother, but the rust resistance is weaker, and it is mostly used for indoor or short-term rust prevention needs.
Common specifications: DN10-DN200, wall thickness 0.5mm-5mm.

3. Galvanized square tube/rectangular tube
Welded from galvanized steel strip, used for building structures, guardrails, doors and windows, etc.

4. Galvanized spiral welded pipe
Mainly used for large-scale water supply, fire protection, pile foundation projects, such as municipal drainage pipes.

5. Galvanized wire casing (KBG/JDG pipe)

Used for building electrical line protection, with fireproof and corrosion-resistant properties.

Read more: Hot-dip Galvanized Seamless Pipe Production Process or ERW pipe vs Seamless pipe