Corrosion of Aluminum Jackets on Aboveground Heat Distribution Systems

摘要

Severe corrosion of aluminum sheet used as a protective jacket on aboveground heat distribution systems has occurred at several military installations. This study was conducted to determine the cause of this corrosion and to recommend revisions to guide specifications on the design, selection and construction on insulation systems on aboveground systems. Used and virgin materials were tested to determine the source of failure. It was concluded that the pitting corrosion of the aluminum resulted from leachable chloride ion in the insulation system. Heavy metal particles contributed to the attack by supplying cathode area. A number of corrective measures were recommended to minimize in future construction: (1) Reduce the acceptable level of leachable chloride ion in the insulation components to 50 ppm, (2) Limit the amount of heavy metals in the insulation system, (3) Require a leaching test of insulation components to ensure that soluble binders have a pH of 6 to 7.5, (4) Design the insulation system to prevent excessive ingress of water from the outside and to prevent condensation of moisture on the inside of this aluminum jacket, (5) Design the vapor control system to prevent significant accumulation of water vapor, and (6) Avoid using a polyethylene coating on the aluminum jacket.