Galvanizing of carbon steel pipe: Selection guide for zinc layer thickness

Hot-dip galvanizing (HDG) is the most commonly used anti-corrosion process for carbon steel pipes. The thickness of the zinc layer directly affects its corrosion resistance and service life. Choosing the appropriate zinc layer thickness requires comprehensive consideration of factors such as the use environment, cost budget, and industry standards. The following is a professional method for scientifically selecting the zinc layer thickness of carbon steel pipes:

Selection of zinc layer thickness for galvanized carbon steel pipe:

International mainstream standards for zinc layer thickness requirements:

1. International standard: ISO 1461

Zinc layer requirements:
≥45μm (normal environment)

≥55μm (harsh environment)

Applicable scenarios: general industry

2. American standard: ASTM A123

Zinc layer requirements:
≥43(1.5mil)
≥85(3.0mil)
Applicable scenarios: heavy anti-corrosion projects

3. Chinese national standard: GB/T 13912

Zinc layer requirements:
≥45μm-55μm (normal grade)
≥80μm (thickened grade)
Applicable scenarios: construction/municipal

4. EU standard: EN ISO 1461

Zinc layer requirements:
≥50μm
≥70μm
Applicable scenarios: marine environment

Zinc layer thickness selection basis:

1. Select according to the use environment

Indoor dry environment:
Recommended zinc layer thickness: 20-45μm (electrogalvanizing or thin hot-dip galvanizing)
Examples: furniture brackets, wire casings, indoor steel structures of buildings

Ordinary outdoor environment:
Recommended zinc layer thickness: 45-80μm (hot-dip galvanizing)
Examples: building guardrails, municipal water pipes

High humidity/coastal/industrial areas:
Recommended zinc layer thickness: ≥80μm (thick hot-dip galvanizing)
Examples: port facilities, chemical plant pipelines

Extremely corrosive environment:
Recommended zinc layer thickness: 80-150μm (special process required, double galvanizing or alloy plating)
Examples: offshore platforms, acid rain areas

2. Select according to industry specifications

Oil/gas pipelines (API 5L):
Buried pipelines: ≥80μm + anti-corrosion coating

Construction industry (GB/T 13912):
Ordinary structural parts: ≥45μm
Key load-bearing parts (such as steel structures): ≥80μm

Electric power communication (YD/T 322):
Wire casing: ≥20μm (electrogalvanizing) or ≥45μm (hot-dip galvanizing)

Risks of insufficient or too thick zinc layer:

1. The zinc layer is too thin
Reason: short galvanizing time/low temperature
Consequence: easy to rust and shortened life

2. Uneven zinc layer
Reason: incomplete pretreatment (such as incomplete pickling)
Consequence: local rust

3. The zinc layer is too thick
Reason: too long zinc immersion time
Consequence: increased brittleness and easy to peel off

Trade-off between cost and zinc layer thickness:
Hot-dip galvanizing cost: for every 10μm increase in zinc layer thickness, the cost increases by about 5%-8%.

Recommended strategy:
General environment: choose 45-60μm (best cost performance).
Harsh environment: Choose 80-120μm (lower long-term maintenance cost).

Calculation of zinc layer corrosion rate:

Zinc corrosion rate in typical environment:
Rural environment: 1-2μm/year
Urban environment: 2-4μm/year
Industrial area: 4-7μm/year
Coastline: 5-10μm/year

Design life formula: Zinc layer thickness = annual corrosion rate × design life × safety factor (1.5-2)

Method for measuring zinc layer thickness:
Magnetic thickness gauge (commonly used): Measure the thickness of non-magnetic zinc layer by magnetoresistance method.
Metallurgical microscope method: Microscopic observation after cutting the sample, high accuracy but damage to the sample.
Weight method (ASTM A90): Calculate the weight of zinc per unit area (g/m²) after dissolving the zinc layer by pickling.
Conversion formula: 1μm ≈ 7.1g/m²

How to choose the zinc layer thickness?

Clarify the use environment (humidity, corrosive media).
Refer to industry standards (such as building pipes ≥45μm, buried pipes ≥80μm).
Balance cost and life (preferably thicker coating for harsh environments).
Test the quality of the zinc layer (ensure uniformity and avoid defects).

Through scientific selection, the anti-corrosion performance and economic benefits of hot-dip galvanized carbon steel pipes can be optimally balanced.

Read more: Galvanized ERW pipe or Galvanized Seamless Steel Pipe