Forensic Issues that Arise from Recirculating Hot Water Systems

Abstract

There has been a significant increase in the failure of pipes used for recirculating hot water systems installed in hospitals, apartment blocks, and hotels in recent years. The rise has occurred as these systems have increased in popularity, and thermostatic mixing valves have made the higher operating temperatures in recirculating systems safe. A common theme tends to be the continuous flow of water above 65°C (150°F) at velocities that have been found acceptable for non-continuous flow. Failures have been experienced in pipes made from both copper and polypropylene random copolymer. Explanations have been slow to emerge and are still subject to debate, particularly as to the initiating causes of pin-hole corrosion (one of the more common modes of failure). Since it is not possible to view the initiation of the pin hole, proof of the cause of the initiation is still unknown. This paper will cover some of the background, myths, and current thinking on the causes of the problem in both copper and polypropylene from the point of view of a forensic engineer trying to make sense of uncertain science and the complications of a problem that is transdisciplinary in nature.