Measurement of zinc coating thickness of galvanized cable trays

Zinc coating thickness on galvanized cable trays is typically measured using non-destructive magnetic induction gauges, ensuring compliance with standards like GB/T 26941.1-2011 and ISO 1461.Standards and Thickness RequirementsFor galvanized cable trays, the minimum zinc coating thickness depends on the tray component and steel thickness. Side and base plates (1.5–3 mm thick) require a local thickness of at least 45 µm (≈325 g/m²), while heavier components (>3 mm) require ≥55 µm. Electro-galvanized trays have lower requirements, typically ≥12 µm. The coating must be continuous, uniform, and free from defects such as bare spots or blisters .Measurement MethodsNon-Destructive MethodsThe most common method is magnetic induction thickness measurement, which is widely used for ferrous metals like steel:Mechanical Gauges: Measure the magnetic pull strength; thicker zinc reduces magnetic attraction.Electronic/Digital Gauges: Measure changes in magnetic flux density; provide accurate readings and can store data for averaging.Pencil-Style or Banana Gauges: Portable options for field inspections; banana gauges allow measurement in any orientation without recalibration . Procedure:Surface Preparation: Clean and dry the tray surface to remove dust, oil, or oxidation.Calibration: Use certified reference standards to calibrate the gauge.Probe Placement: Position the probe perpendicular to the surface.Multi-Point Measurement: Take readings at multiple points to account for coating variability.Data Evaluation: Compare readings with required specifications to verify compliance .Destructive MethodsGravimetric (Stripping and Weighing): Measures the mass of zinc per unit area; used for arbitration or verification.Optical Microscopy: Cross-sectional analysis of the coating; typically used to resolve disputes or for research purposes .ConsiderationsDuplex Coatings: If paint or powder is applied over galvanized steel, specialized gauges can measure both layers simultaneously.Accuracy: Multiple readings and averaging are recommended to compensate for substrate roughness, curvature, and other factors .Compliance: Ensure measurements meet relevant standards such as GB/T 26941.1-2011, ASTM A123/A153, or ISO 1461, depending on the application and region . Using these methods ensures that galvanized cable trays have adequate corrosion protection and meet engineering and industry standards.