THICKNESS TESTING OF 316 L COATING

[Vijay Deshpande]

Which is the best metod to check thickness of arc sprayed 316L coating on mild steel substrate
Vijay Deshpande

[Gordon]

Hi Vijay

The best way would be to physically measure thickness with a micrometer or vernier type instrument. Using electronic devices (see quote from another thread) will have problems with this combination of coating and substrate. You may initially think that a non-magnetic 316 stainless steel wire would produce a non-magnetic coating and thus be suitable for measurement using a magnetic method as you would with a zinc coating. Unfortunately, 316 stainless often becomes slightly magnetic after spraying. The magnetic testing method can be used, but you need to be very careful to calibrate the instrument using known coating samples and not just relying on the plastic calibration shims.

Hi Aturas

There are many portable electronic thickness measuring devices out there. Ideally, the ones using both magnetic and eddycurrent methods would best suit your needs. Select the models that cover your particular thickness measuring range. These devices are good for:

* non-magnetic coatings on ferromagnetic substrates like aluminium on steel
* non-electrical conductive coatings on conductive substrates like ceramic on austenitic (non-magnetic) stainless steel


You will find that these instruments will not work with every coating/substrate combination though. Always calibrate and test on specific coating/substrate materials before relying on their readings.

The measurement of metals on non-ferrous metal substrates is not easily achieved using eddy-current method unless there is a 3:1 ratio in the conductivity between substrate and coating. The calibration of instruments must be carried out using samples of the materials with known thickness. Such instruments do not use the normal calibration characteristics and would have to be specially made for the specific coating and substrate.

Regards Gordon