I take the questions to be "Can the roof plate be welded to the supporting roof structure?" and "Can the roof plate be painted prior to welding?"
On the first issue, yes, the roof plate can be welded to the supporting roof structure, but this also affects whether the roof is considered frangible. There are various pros and cons of doing so.
On the section question, I don't believe API addresses it at all. It is fairly common to shop-prime roof plates prior to welding, but they will require extensive touch-up after welding, and the procedure should be approved beforehand. Typical paint specifications would spell out if this was permissible, optional, or prohibited.
I take the questions to be "Can the roof plate be welded to the supporting roof structure?" and "Can the roof plate be painted prior to welding?"
On the first issue, yes, the roof plate can be welded to the supporting roof structure, but this also affects whether the roof is considered frangible. There are various pros and cons of doing so.
On the section question, I don't believe API addresses it at all. It is fairly common to shop-prime roof plates prior to welding, but they will require extensive touch-up after welding, and the procedure should be approved beforehand. Typical paint specifications would spell out if this was permissible, optional, or prohibited.
As JStephen pointed out, welding of painted steel - paint/primer actually touching the weld - requires a new WPS, qualified with a PQR coupon with that paint/primer applied to the coupon. And yes, it is worth doing; deoxyaluminate weldable primer is very nice stuff, and keeps the metal from rusting after being delivered to the field. The total hours involved with cleaning rust off of weld prep areas is a significant part of your welding expense. Cheaper to shop-prime those spots with a weldable primer.
