We are applying coatings to the inside of metal food storage tanks, but a preferred primer is not FDA compliant. Can we apply a UV curable coating...

that complies with FCN 772 over the primer as a functional barrier to comply with FDA regulations?

A functional barrier must assure that any potential migration of FDA non-compliant substances not in contact with food or beverages is below the “Threshold of Regulation”, i.e. less than 50 ppb in the food. If a coating that complies with FCN 772 is to function as a functional barrier, it must meet three criteria:
1. The UV cured coating must meet all of the composition and extractable monomers and total extractable solids requirements of FCN 772.
2. The UV cured coating must demonstrably prevent migration of any of the uncleared primer components into the food at levels above 50 ppb.

Both of these requirements must be demonstrated by conducting extraction tests with appropriate food simulants as specified in Appendix II, SELECTED MIGRATION TESTING PROTOCOLS, at the FDA Preparation of Premarket Submissions for Food Contact Substances: Chemistry Recommendations web site http://www.cfsan.fda.gov/~dms/opa3pmnc.html#aii.

3. The UV coating must reasonably be expected to continue to serve as an effective functional barrier over the lifetime of the manufactured article (food storage tank).

The design of the tank for the intended application, the compositions of the primer and coatings, and the design and results of the extraction testing protocols and results should be subjected to qualified legal review to assure compliance with FDA regulations.