The instructions mention nothing of painted pipes. I've used two with 15mm pipes that had layers of paint.
Paint on the pipe shouldnt be an issues if you remove a high percentage and create a SMOOTH area.
The paint might make it difficult to tighten using instructions given. Start on a low torque (as instructed) and slowly increase the torques (not as instructed) between each shoulder bolt, still alternating between each bolt (as instructed.), untill both sides of the casing are flush.
If you rush tightening you can crack the frame and cause the device to leak.
If you dont tighten enough (due to following instructions), you'll have a massive leek on your hands. You can still tighten the bolts while it leaks and hopefully close the gap between the two sides of the casing.
I
I brought one of these for an emergency water leak and stop tap being inaccessible.. followed instructions to the letter.. the thing got stuck and twisted the pipework.. I had to go back to basics and snatch a live cold main but that worked apart from getting wet.
Used may and so long as the pipes are clean and round they have always worked really well
