EN ISO 21968:2019 PDF

Overview

EN ISO 21968:2019 - Non-magnetic metallic coatings on metallic and non-metallic basis materials - Measurement of coating thickness - Phase-sensitive eddy-current method (ISO 21968:2019) is a CEN-endorsed international standard that defines a non-destructive testing procedure for measuring the thickness of non-magnetic metallic coatings. The standard covers use of phase-sensitive eddy-current instruments for coatings such as zinc, cadmium, copper, tin or chromium on steel and copper or silver on composite materials.

Key advantages highlighted:

• Designed for coating thickness measurement on small surface areas and strong curvatures.
• Less affected by substrate magnetic properties than amplitude-sensitive eddy-current methods (see ISO 2360).
• More sensitive to the electrical properties of the coating.

Key Topics

The standard addresses technical requirements and measurement practice, including:

• Principle of measurement: phase-sensitive eddy-current detection and interpretation.
• Factors affecting measurement uncertainty:
  • Electrical properties of the coating
  • Geometry: base material thickness, edge effects, surface curvature
  • Surface roughness, lift-off, probe pressure and tilt
  • Temperature effects, intermediate coatings, external electromagnetic fields
• Calibration and adjustment of instruments, including use of thickness reference standards and adjustment methods.
• Measurement procedure and evaluation: sampling, number of measurements, data treatment.
• Uncertainty and precision: methods for estimating combined and expanded uncertainty, repeatability (r) and reproducibility (R).
• Informative annexes with uncertainty estimation, basic performance requirements for gauges, and experimental examples.

Important technical condition: measurement on metallic substrates requires that the product of conductivity (σ) and permeability (μ) of one material be at least twice that of the other material for valid results.

Applications

EN ISO 21968:2019 is practical for industries and professionals who need accurate, non-destructive coating thickness measurement:

• Quality control and inspection in plating, galvanizing and surface finishing operations
• Automotive, aerospace and marine component inspection where corrosion-protection coatings are applied on curved parts
• Composite manufacturing with metallic overlays (e.g., copper or silver coatings)
• Corrosion protection auditing and research laboratories
• Manufacturers and suppliers of eddy-current coating thickness gauges

Who Should Use This Standard

• Coating inspectors and NDT technicians
• Surface treatment and plating engineers
• Metrology and QA/QC personnel
• Instrument manufacturers and calibration laboratories

Related Standards

• ISO 2360 - amplitude-sensitive eddy-current method (for comparison and where amplitude methods are applicable)
• ISO/IEC Guide 98-3 (GUM) - for uncertainty estimation approach referenced in the standard

EN ISO 21968:2019 provides practical guidance and metrological procedures to ensure reliable, repeatable phase-sensitive eddy-current measurements of metallic coating thickness in demanding geometries and applications.