1. Corrosion is Oriented Vertically – the pattern associated with the corrosion by-product deposits and the actual metal loss indicate that the entire piece of pipe is filled with trapped air. The physical evidence indicates that the corrosion is longitudinal along the vertical axis of the pipe.
2. Evidence of Evaporation/Condensation – the underside of the riser check valve indicates that water is condensing and dripping off of the clapper. In this process water evaporates from the pool at the bottom of the pipe and rises up to re-condense at the top of the pipe. As the liquid condensate water then runs down the pipe dissolved oxygen from the trapped air reacts with the sidewalls of the pipe.
3. Oxygen Depletion Corrosion – the oxygen depleted zone in rolled groove connections shows evidence of oxygen corrosion. When the pipe ends become anodic, they become “hot spots” for rapid acceleration of the metal loss.
4. Under-Deposit Oxygen Acceleration – as the corrosion by-product builds on the vertical walls of the pipe the corrosion rate accelerates. The net effect is a continuous build-up of corrosion debris on the sidewalls of the pipe until a pinhole leak occurs.
5. Weld Seam Corrosion – the weld seam in the vertical piping is vulnerable to oxygen corrosion attack. Piping that is used in fire sprinkler systems is not heat annealed and as such is subject to weld seam attack as evidenced in the pictures of the metal loss on the piping.