ASME B31.3 Pressure Testing Painted Welds
Can welds be painted before conducting a Pressure Test?
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 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, as discussed in the following section.
Can welds be insulated before conducting a Pressure Test?
ASME B31.3 paragraph 345.3.1(a) requires that welds remain un-insulated for pressure testing with two exceptions
ASME B31.3 paragraph 345.3.1 (b) : welds or joints pressure tested before being insulated, typically fabricated spools tested in a shop, can be covered by insulation before the field welds are pressure tested. This requires a quality system that can track which welds were included in each pressure test and if the joints were properly exposed during their respective test.
ASME B31.3 paragraph 345.3.1 (c) : with the facility owners approval, and at their discretion, joints in Category D Fluid Service that are subject to hydrostatic pressure testing may be insulated including the sheathing, lagging, or cladding weather protection prior to pressure testing. If this practice is permitted work instructions or pressure testing procedures should address this scenario, to ensure detection if thereleaks. Practices such as increasing the required test duration should be implemented as it allows for even small leaks to pass through the insulation sufficiently enough to allow detection.
Practical Considerations
Painting welds before pressure testing can mask leaks or defects that would otherwise be visible during the test. For example, paint might temporarily seal small leaks, leading to an acceptable test during hydrostatic or pneumatic testing. There is a risk of small masked leaks due to the coating to begin to leak after passage of time, allowing the leak to occur during operation.
Some facilities may have conditional allowance for when this practice is acceptable depending on the criticality of the piping system. Owners can perform risk assessments on the different fluid types that are in their facility, where the lower risk systems can be primed or painted, and the higher risk systems would remain bare before any pressure testing is completed.
If you have a specific project specification or situation, consult the piping engineer or owner’s inspector for guidance.