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Coating Dry Film Thickness (DFT) Measurement Log Worksheet

Dry film thickness records are among the most frequently asked-for documents when pipe, vessels and skids are coated. This worksheet calculates the average, lowest reading and margin to the specification for each spot, then exports the log.

Download:

Spot average (um)	Lowest reading (um)	Margin to spec (um)
71.6667	68	11.6667
262.3333	255	22.3333
244.6667	238	4.6667
133.3333	128	8.3333
51	46	1

Spots logged

Worst margin to spec

Average of spot averages

152.6

Units are micrometers (um); 1 mil is 25.4 um. A spot is commonly the average of several gauge readings, and SSPC-PA 2 style practice takes five spots per 100 square feet of area, but your project specification controls the plan and the acceptance limits. A low individual reading may still be rejected even when the average passes.

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How to use this worksheet

Enter the item or area, the coat, and the minimum DFT from the coating specification. Type the three gauge readings for each spot. The sheet calculates the spot average, the lowest reading and the margin between the average and the specified minimum. A negative margin means the average is below specification and the coating needs recoating or additional film. Export to Excel for the inspection report or to PDF for the data book.

Measurement practice

Magnetic and eddy current gauges must be calibrated on a reference plate with a shim near the expected thickness, and the readings taken on a surface profile that is accounted for. Common standards such as SSPC-PA 2 and ISO 19840 describe how to take spot and area measurements and how to treat individual low readings. Projects often allow a limited percentage of readings below the minimum, but only within a stated floor, so read the specification closely.

Calibrate the gauge before each shift
Account for blast profile on bare steel
Take readings away from edges and welds unless specified
Record gauge serial number and calibration reference

Common mistakes

Typical errors include measuring wet film and reporting it as dry, averaging across different coats and not recording the gauge calibration. Another is checking only the average and ignoring individual readings that fall below the specification floor. Keep the primer, intermediate and topcoat rows separate so each layer's thickness can be traced, and add a total system row after the final coat.

Frequently Asked Questions

Does a passing average mean the coating is accepted?

Not always. Many specifications limit individual readings as well as the average, for example no reading below a stated percentage of the minimum. The worksheet shows the lowest reading so you can compare against that rule.

How many readings per spot?

Practice varies. SSPC-PA 2 style methods average a few gauge readings per spot, and ISO 19840 uses its own rules. Use your project's method and edit the readings columns if you need more.

Can I use mils instead of micrometers?

Yes. Enter the values in mils consistently for all columns, or convert by multiplying mils by 25.4 to get micrometers. The calculations work in any unit as long as you do not mix them.

Is wet film measurement acceptable?

Wet film readings guide application but do not replace the dry film inspection after curing. Record DFT after the coating has cured according to the paint data sheet.

If coating inspection results are collected on paper and rekeyed, we can help build a private workflow that captures readings once and feeds the quality record in your ERP.

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