Pressure vessels not subject to internal corrosion shall receive a certificate

Pressure vessels not subject to internal corrosion shall receive a certificate inspection biennially, but internal inspection shall not be required of pressure vessels, the contents of which are known to be noncorrosive to the material of which the shell, heads or fittings are constructed, either from the chemical composition of the contents or from evidence that the contents are adequately treated with a corrosion inhibitor, or from evidence that vessel parts are isolated from the contents with a corrosion resistant lining, provided that such vessels are constructed in accordance with the rules and regulations of the Board, and provided further that evidence proving noncorrosiveness is approved by the Board.