Soak the studs the threaded part with Wd40 and if you get the nuts slack work the nut back and forwards till the nuts of and hopfully you won't snap the stud or take the car for a run every thing gets warm then give the nuts a spray with Wd40 the downpipe won't go on fire with doing this Wd40 just gives of white smoke and do the working back and forth of the nut till the nut is of