SS 316L Coating thickness measurement

[sumant]

Hi again!

I have applied SS 316L coating by wire arc spray over carbon steel. But totally failed to measure coating thickness by Magnetic Induction method. The actual thk by micrometer shows 1.05 mm but thk guage shows 0.6++ only. DFT meter was calibrated & recalibrated. It works fine on other coatings.

Can anybody inform -

a) why it is happening?
b) what DFT meter will give correct readings?

Regards,

[Gordon]

Hi sumant

316 is an austenitic stainless steel and is normally non-magnetic. Thermal spray coatings produced from this material though show different properties and usually show some ferromagnetic properties unlike its wrought equivalent. It is the coatings magnetic properties that are causing your instrument to give you false low readings of coating thickness. Really, the only way round this is to calibrate your instrument using your actual coating and not with the usual non-magnetic plastic shims.

See this thread

[bhellman]

Hi Sumant
I don't know if this is of any value, but just as info. All thermally sprayed coatings are subject to a certain level of forging in the spray process. As higher the particle velocity and inpact force is, that higher the forging effect (unregarding particle size). That is one part of the calculation of the finishing allowance required.
br bjarne

[bhellman]

Sumant
One thing more, as Gordon explained, the magnetic properties make a hugh difference. You have to be certain about which measuring system is used for a certain material.
You have also to remember that the ts-coating, because of its splittered construction, does many signals/coils/acustics and so on to behave oddly.
bhe

[bhellman]

Still more about thickness measuring.
If trying to use magnetic methods, the only somewhat accurate system is to first make accurate test samples (mechanically measured) for calibrating the magnetic-meter.
Even then one has to remember that the magnetic flow is depending on the material thickness.