DeFelsko's PosiTector 6000 FNDS Coating Thickness Gauge non-destructively measures the individual thicknesses of paint and galvanized zinc layers in double-sided coating systems with a single reading.
background
Steel corrodes when an electrolyte, such as water, connects the anode and cathode on the steel surface. The formation of corrosion holes can lead to flaky iron oxides, known as rust.
To avoid rust, measures need to be taken to prevent the formation of corrosion pools. Two common methods of preventing steel corrosion are:
1. Cathodic protection (by using sacrificial anodes).
2. Form a barrier layer to prevent the electrolyte from contacting the steel.
Double coating is a combination of both cathodic protection (galvanizing) and barrier layer (paint or powder coating).
application
Dual phase coating systems combine two corrosion protection systems – usually paint or powder coating (hot dip, electroplating or zinc spray metallization) on galvanized steel. The corrosion protection produced by a two-coat system is superior to either protection system used alone.
Advantages of the two-coat system:
Extends the life of the coating system and underlying substrate
Delayed maintenance intervals - fewer patch repairs, lower maintenance costs
color coding
aesthetics
measurement challenge
Measuring the thickness of these layers with conventional instruments is challenging.
Typically, the thickness of the zinc is first measured with a magmeter such as PosiTector 6000 F1 or PosiTest DFT Ferrous. Then use the same instrument to measure the total thickness of the zinc and paint layers. The difference between the two readings is considered the thickness of the paint layer. This method assumes that the thickness of the zinc never changes.
In practice, the thickness of zinc is not always uniform throughout a part or structure. Coating thickness depends on the thickness, roughness, chemistry and design of the galvanized steel. Any or all of these factors can produce galvanized coatings of uneven thickness.
The second conventional method uses a combined magnetic and eddy current probe, such as the PosiTector 6000 FN3. Two readings are taken, the first reading in eddy current mode for paint thickness and the second reading in magnetic mode for total coating thickness.
The difference between the two readings is considered the thickness of the zinc layer. Also, this method assumes that the zinc thickness does not vary across the structure.
Both methods are time-consuming and error-prone. The PosiTector FNDS duplex probe does this with one read, simply and accurately.
DEFELSKO's solution
The PosiTector 6000 FNDS Dual Coat Thickness Gauge measures both the individual thickness of the paint and the zinc layer in a dual-coat system with a single reading.
In duplex mode, the PosiTector 6000 FNDS uses both magnetic (ferrous) and eddy current (non-ferrous) principles to calculate and display the thickness of individual paint and zinc layers.
The magnetic principle is used to measure the total paint/zinc thickness on ferrous substrates, while the eddy current principle is used to measure the paint thickness on colored zinc coatings.
Zinc thickness is calculated by subtracting the paint thickness from the combined paint/zinc thickness measurement.
When not in duplex mode, the meter operates like a traditional ferrous/non-ferrous combinatIon Meter (similar to the PosiTector 6000 FNS probe). Ideal for measuring non-magnetic coatings on steel and non-conductive coatings on non-ferrous substrates.
