Dry Film Thickness Gauge

Definition - What does Dry Film Thickness Gauge mean?

A dry film thickness gauge is a tool or instrument used to measure the dry film thickness on a metal or nonmetal substrate and compare it to approved standards.

Some dry film thickness gauges just display measured values, while other models include some or all of the following features: memory for hundreds of readings, the ability to send data to a portable printer, computation and analytical presentations of readings, battery power and audio to alert the user of any readings that are out of specs.

Dry film thickness is important in the coatings industry because it is a determining factor in the quality, reliability and longevity of a coated product or structure.

Corrosionpedia explains Dry Film Thickness Gauge

There are various types of gauges to determine dry film thickness as specified based on the applicable measurement method. This can be either destructive or non-destructive as defined by industry groups or authorities like the Society for Protective Coatings (SSPC), ASTM International, the International Maritime Organization Performance Standard for Protective Coatings, or the International Organization for Standardization (ISO).

The dry film thickness gauge has been an essential tool in making sure that coating thicknesses are within specifications. Modern technology has helped manufacturers to produce dry film thickness gauges that are smaller in size but packed with more features that make measurement easier, faster and more accurate.

There are different types of dry film thickness gauges designed for each measurement method – non-destructive magnetic, beta backscatter, ultrasound or ultrasonic, and eddy current. The micrometer and paint inspection gauge (PIG) are two instruments used for destructive thickness measurement methods.

The appropriate type of dry film thickness measurement procedure/gauge depends on the following:

  • Coating/ substrate combination
  • Substrate thickness
  • Range of gauge readings and other features like statistical data capability
  • Designed accuracy of the instrument as stated on the manual or data sheet
  • Cost
  • Other features that may be required for the project

The following are some of the good measurement practices observed to obtain the most accurate results possible:

  • Compliance to required calibration frequency
  • No measurements on soft or partially cured coatings, close to a hole or the edges of the coated surface
  • Cleanliness of the gauge probe; dirt and other foreign particles will prevent true contact between the probe and the coated surface
  • The avoidance of excessive probe pressure, which may result in erroneous readings
  • The consideration of environmental conditions like extreme temperatures because they can affect the gauge’s readings

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