Understand how galvanizing thickness affects corrosion protection, how steel thickness determines acceptance requirements, and what additional protection coastal and industrial projects may need.
Hot-dip galvanizing is widely used to protect steel CCTV and lighting poles against corrosion. However, describing a pole as “galvanized” does not fully define its protection level, and an 85 μm coating alone cannot establish its service life.
At the enquiry stage, confirm the applicable standard, steel thickness, coating measurement criteria, exposure conditions and repair requirements so that quotation and acceptance criteria align. This guide gives system integrators, buyers and inspectors a practical sequence for reviewing these requirements.
Galvanizing standards generally specify minimum coating requirements according to article type and steel thickness. The table below summarizes the usual thickness requirements for non-centrifuged steel articles in EN ISO 1461:2022. It must not be applied indiscriminately to all fasteners or special components.
| Steel thickness | Minimum local coating thickness | Minimum mean coating thickness |
| >6 mm | 70 μm | 85 μm |
| >3 mm and ≤6 mm | 55 μm | 70 μm |
| ≥1.5 mm and ≤3 mm | 45 μm | 55 μm |
| <1.5 mm | 35 μm | 45 μm |
A 6 mm steel plate falls in the “>3 mm and ≤6 mm” category. It is therefore incorrect to state that the standard requires an average coating thickness of 85 μm for all steel with a wall thickness ≥6 mm. If a project requires an average of 85 μm on steel 6 mm thick or thinner, specify this as a project requirement in the order and confirm feasibility before manufacture.
The pole shaft and base plate may fall into different thickness categories. Measurements on a thick base plate cannot substitute for measurements on a thin-walled shaft.
For projects specifying ISO 1461, a regional adoption of that standard, or GB/T 13912, confirm the contractual edition and applicable clauses. North American projects may specify ASTM requirements. Matching thickness values alone do not establish equivalence between standards.
Differences in steel chemistry can affect the galvanizing reaction rate and coating adhesion. Acceptance should therefore consider coating uniformity and adhesion testing as well as thickness.
2. Does a Thicker Coating Mean a Longer Service Life
Under comparable atmospheric exposure, a thicker, compliant zinc coating generally provides protection for longer. Actual performance also depends on the local corrosion rate, coating defects, and details that retain water.
Distinguish between the coating’s protective capability, the time to an agreed maintenance condition, and the overall service life of the pole. First maintenance of the coating does not mean the pole must be replaced. Nor can overall pole life be determined from galvanizing thickness alone.
Avoid blanket claims such as “85 μm lasts 20 years” or “15 years within 1 km of the coast.” Any durability assessment should state the exposure basis, assessment method, maintenance endpoint, and assumptions.
Zinc can provide sacrificial protection to small adjacent areas of exposed steel. This does not mean scratches or uncoated areas can be ignored. Assess repairs against the damage, applicable standard, and project requirements.
3. Select Protection for Coastal and Industrial Projects
Distance from the coast is useful preliminary information, but it cannot establish a corrosivity category on its own. Prevailing winds, salt deposition, time of wetness, pollution, sheltering and direct seawater splash all affect corrosion.
Check whether the site involves any of the following:
■ Seawater splash, tidal exposure or frequent saltwater contact;
■ Industrial pollution, chemical exposure or prolonged high humidity;
■ Water traps around access doors, base plates or inside the shaft;
■ Difficult cleaning or maintenance access, or an extended time-to-first-maintenance target;
■ Specific requirements for colour, gloss and appearance retention.
Where duplex protection is required, specify galvanizing and the subsequent coating as a compatible system. Include preparation of the galvanized surface, primer and topcoat or powder coating system, dry film thickness, adhesion, weathering performance and repair methods. “Marine-grade topcoat” or “powder coated” is not a complete specification.
Assess direct splash and immersion exposure separately. Do not apply service-life assumptions for ordinary atmospheric exposure directly to these conditions.
4. Galvanizing Quality Control and Delivery Requirements
●Thickness Measurement and Reporting
Determine local coating thickness using the reference areas and measurement rules in the applicable standard, rather than an arbitrary single gauge reading. Reports should identify the component or batch, applicable thickness category, sampling and measurement areas, instrument details, results, and acceptance criteria.
Where paint or powder coating is applied over the zinc, the total thickness measured by a conventional magnetic gauge cannot be treated as zinc thickness. Agree on separate inspection methods for galvanizing and the subsequent coating at the quotation stage.
●Appearance and Functional Checks
Check for uncoated areas, zinc build-up that interferes with use, and sharp projections. Review protection at welds, the underside of base plates, access-door edges and specified internal surfaces. Ensure threads and mating parts remain functional.
Differences in colour or local gloss alone are not grounds for rejection. Assess surface defects against the standard, intended function and project appearance requirements. Assess white corrosion products according to their extent and the remaining coating.
●Repairs and Associated Components
Treat renovation of uncoated areas at the galvanizing plant separately from repairs to transport or installation damage, applying the relevant requirements to each. Record repair location, area, surface preparation, materials and repair coating requirements. A note stating only “silver paint applied” is insufficient.
Specify suitable corrosion protection for fasteners, considering thread fit, material combinations and actual exposure. Do not impose one coating thickness on every component without considering its application.
Q: Is a Thicker Coating Always Better?
A: Do not pursue thickness in isolation from process control, adhesion, assembly requirements, and exposure. Coordinate coatings above the usual thickness requirements with the fabricator and galvanizer in advance. Silicon, phosphorus, and other constituents in the steel can also influence the reaction and coating formation.
Q: Do Coastal Projects Always Need Powder Coating
A: No. Compare galvanizing alone with a duplex system against site exposure, the target maintenance interval and project specifications. Any subsequent coating must suit both the galvanized substrate and the environment.
Q: Can One Measurement on the Shaft Establish Acceptance
A: No. Sampling, reference areas, and measurement locations should follow the standard and inspection plan, covering the different steel thicknesses and critical areas requiring inspection.
Q: Share Site Conditions for Corrosion Protection Advice
A: Provide the project location, site photos, main component thicknesses, and corrosion protection specification to help review coating categories, duplex protection needs, and inspection scope. If information is incomplete, send what is available so that the remaining inputs can be identified.
