ASME B31.3 paragraph 345.3.1(d) states: All joints may be primed and painted prior to leak testing unless a sensitive leak test is required.

The code therefore allows for joints to be primed and or painted for pressure testing, but the owner’s specifications or site practices may prohibit it. It is important to know what requirements may supersede what the code allows before implementing this practice.

Even with the allowance for primer or paint, insulation is treated differently.