At MCL Solar, we treat hot-dip galvanizing as a service-life control—not a cosmetic finish. Solar street light poles, arms, base plates, anchor cages and mounting brackets spend years outdoors, often in humidity, road spray, dust and coastal air. A weak zinc layer can become the hidden failure point long before the LED, battery or solar panel reaches its design life.
This article explains how we translate GB/T 13912-2020, Metallic coatings—Hot dip galvanized coatings on fabricated iron and steel articles—Specifications and test methods, into a practical supplier, inspection and delivery checklist for solar street light projects.
Our engineering position: corrosion protection starts before the zinc bath
Hot-dip galvanizing immerses a pre-treated steel article in molten zinc and forms a zinc and zinc–iron alloy coating on the steel surface. The coating is designed primarily for corrosion protection. Color uniformity matters for appearance, but coating continuity, thickness and handling quality matter more for long-term performance.
For MCL Solar projects, galvanizing is reviewed together with steel grade, wall thickness, weld quality, drainage and venting, lifting points, packing and the final installation environment. A certificate alone is not enough; the delivered parts must match the drawing, the agreed coating requirement and the inspection record.
1. What must be controlled before galvanizing?
The same steel part can produce different zinc results because of its chemistry, surface condition, mass, geometry and galvanizing conditions. Our pre-treatment review focuses on the following:
- Steel and surface condition: remove oil, paint, heavy scale, welding slag and other contamination that can block the reaction between steel and zinc.
- Weld quality: continuous, clean welds reduce trapped solutions and help prevent seepage or local coating defects around joints.
- Drainage and venting: closed cavities and blind pockets need a safe path for cleaning solutions, zinc entry and air release. The final hole arrangement must be agreed with the drawing and structural requirements.
- Handling points: lifting marks and contact points should be planned so they do not create uncoated or badly damaged areas on significant surfaces.
- Environment: coastal, industrial, humid or high-salt projects may require a thicker coating, duplex paint system or additional protection agreed before production.
2. Acceptance requirements: appearance is only the first gate
Unless a project specification states otherwise, acceptance is normally performed before the galvanized parts leave the galvanizing facility. It includes visual assessment and coating thickness measurement. Adhesion testing is not normally required unless the buyer and supplier agree on it before production.
| Inspection item | What we look for | Why it matters |
|---|---|---|
| Significant surface | The visible or performance-critical area defined for appearance and service. | Not every hidden edge carries the same visual or functional importance. |
| Appearance | At a viewing distance of more than 1 m: no harmful runs, zinc spikes, peeling, uncoated areas or remaining flux residue on significant surfaces. | These defects may affect safety, assembly, appearance or corrosion protection. |
| Color variation | Dark gray, light gray and network-like patterns may be acceptable when thickness and service performance are compliant. | Galvanizing is primarily corrosion protection, not decorative painting. |
| Wet storage | White rust can occur during damp storage; it is assessed together with coating condition, exposure history and thickness. | Storage and packing can influence the appearance after galvanizing. |
| Weld seepage | Minor appearance effects at intersecting welds are not automatically a rejection reason; functional impact must be assessed. | Some geometry-related effects cannot be eliminated without changing the design. |
3. Coating thickness: local values and average values are different
A reliable inspection record should distinguish local coating thickness from mean coating thickness. A local value describes the arithmetic average measured on one reference area. A mean value is the average across the defined measurement areas for a part or inspection lot. The required minimum depends on the steel thickness range and the applicable project specification.
For long poles and brackets, we define reference areas that represent the real service surface—not only the easiest location to measure. For large articles, the supplied technical note recommends at least three reference areas per article. Each reference area should contain at least five measurement points, and the arithmetic average is used for the area result. The final acceptance decision must follow the applicable table and purchase specification.
4. Which test method should be used?
| Method | Typical use | MCL Solar recommendation |
|---|---|---|
| Magnetic method | Routine, non-destructive coating thickness checks on suitable steel surfaces. | Use for production control and incoming inspection when the substrate and geometry are suitable. |
| Gravimetric method | Coating mass per unit area is measured by weighing; the result can be converted to thickness. | Use as the arbitration method when test results are disputed, understanding that it may damage the part. |
| Cross-section microscopy | Optional section-based evaluation of coating structure and thickness. | Use when geometry or a technical dispute requires additional evidence. |
In practice, a magnetic gauge is efficient and protects the part. However, the gauge must be calibrated or verified, the substrate condition must be suitable, and measurement locations must be recorded. A single attractive reading is not a batch acceptance decision.
5. Defect handling and repair
When a small uncoated area is found, the correct response is not to cover it casually with ordinary paint. The area must be cleaned thoroughly, and the repair material and thickness must be compatible with the original zinc system and the intended service environment.
- The supplied technical guidance limits the total repaired uncoated area to 0.5% of the article surface.
- A single uncoated area larger than 10 cm² should be re-galvanized rather than treated as a minor touch-up.
- Approved repair routes may include thermal zinc spraying, zinc-rich coating or zinc-alloy cladding, subject to the project specification.
- The repair layer is typically required to be at least 100 μm in the described acceptance route and must provide sacrificial-anode protection.
- If a duplex paint system will follow, the galvanizing and repair method must be agreed before production.
If a sampled article fails, the lot should be handled according to the agreed sampling plan. The supplied technical note describes double sampling for reinspection when the original sample fails; if the reinspection still fails, the nonconforming pieces require rejection or re-galvanizing with the buyer’s approval.
6. Our MCL Solar project checklist
- Before quotation: confirm steel thickness ranges, significant surfaces, corrosion environment, coating requirement, repair route and whether painting will follow.
- Before galvanizing: review drainage and venting, weld cleanliness, lifting points, inspection areas and the sampling plan.
- During inspection: check appearance from more than 1 m, measure representative areas, record instrument and locations, and separate different steel-thickness ranges into the correct inspection lots.
- Before shipment: verify dimensions, threads, bolt fit, base-plate flatness, coating damage from handling, packing dryness and the final inspection record.
- At site: prevent dragging or impact damage, keep repaired surfaces compatible with the agreed system, and record any field touch-up before installation is closed.
What should a buyer request from a solar street light supplier?
- Steel material and thickness range for each part.
- Galvanizing standard and any project-specific coating requirement.
- Inspection-lot definition and sample quantity.
- Visual inspection record and coating-thickness measurement map.
- Gauge identification and calibration or verification evidence.
- Nonconformance, repair and reinspection records.
- Photos of critical parts before packing, especially base plates, welds, brackets and threaded connections.
Conclusion: specify the coating, verify the coating, protect the whole system
A solar street light is an outdoor system. Its reliability depends on the weakest exposed component, and that component is often a steel pole connection or bracket rather than the lamp itself. By reviewing the design before galvanizing, measuring representative areas, using the correct test method and documenting every repair, MCL Solar helps buyers reduce premature corrosion risk and avoid disputes at delivery.
For a project-specific recommendation on pole material, bracket design, galvanizing, lighting performance and solar sizing, contact the MCL Solar engineering team. You can also review our related guides on lumen selection, beam angle and solar panel sizing.
Technical note: This article is an engineering interpretation for project communication and supplier coordination. The signed purchase specification, applicable local requirements and the current edition of the referenced standard govern final acceptance.