How chromium specimen Test is representative?

[edelvi]

Chromium adherence on the globe surface of one Globe Valve will be evaluated according to ASTM B 571 in a specimen. Company in charge of the chromium coating carry out the process in different cells: one for the globe and one for the specimen because the big difference in size, shape and surface. Of course calculation is done for each particular case: time, amperes, surface area, etc.
I consider that the chromium coating on the specimen is not representative with respect to the one obtained on the globe.
Please, let me know if is possible to obtain the identical coating in both specimen and globe at the same time and process.

Thanks in advance

 

[kenvlach]

If by "in different cells" you mean different plating tanks (rather than anode partitions within the same tank), I agree.* ASTM B571, Paragraph 2.8:
"...test panels shall be of the same material and have the same surface finish as the item to be tested and shall be processed through the same preplating, electroplating, and postplating cycle with the parts they represent."
The emphasised same is in the original ASTM wording.

*If the small test tank was filled with solution from the larger work tank, especially with continuous circulation betwen tanks, this may be considered the same plating solution. A bit ambiguous; perhaps specify test panel to be plated within the same plating tank concurrently with production.

Most methods within ASTM B571 are rather destructive. Try the Peel Test (Para. 11) using adhesive tape.
Presuming a steel substrate, I suggest also checking thickness using a magnetic tester (the cheap, 'pull-off' kind also used for paint & galvanize thickness). Very easy. For greater accuracy, use coated standards for calibration -- ASTM B499 or ISO 2178.

ASTM B571, 'Standard Practice for Qualitative Adhesion Testing of Metallic Coatings.'

http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/B571.htm?L+mystore+esxw6604