I deal with inspections on boilers and ressurized piping as a ASME inspector and after the final weld blending, we perfrom NDE, mostly dye penetrant in an effort to find cracks that are not clearly visible to the eye.
In this case I would certianly do a PT check before pressurizing it. A cheap method is to use some light machine oil, like a 5 weight or less, thoroghly soak the area as well as the HAZ adjacent to the weld, and let it soak in the oil for about 10-15 minutes after brushing it on. Then wipe off the excess oil with a clean rag, apply some alcohol to the rag but don't saturate it,then wipe the area again. give it five minutes to air dry, then sprinkle some talcum powder very lighly over the repair area.
The talcum powder will draw the oil out of any fine cracks and will be clearly visible to the eye after a few minutes,or if its bad enough, the powder will stick to the area with the indication.
Cheap but effective and will give ya peace of mind.