The most common point of failure on fire sprinkler piping is at weld seams and welded outlets. The high temperature experienced during the welding process changes the metal structure and creates a Heat Affected Zone (HAZ). Weld seam failure is commonly mistaken as a material defect in the pipe, but it is, in fact, a highly reactive anodic lo, in fact, related during the manufacture or fabrication of the pipe that will corrode preferentially to the rest of the pipe. The only way to stop weld seam corrosion in particular and oxygen corrosion, in general, is to completely eliminate oxygen from the fire sprinkler piping.
Learn more about how to detect and monitor corrosion here.