Environmentally Assisted Cracking (EAC) of copper tubes in high rise residential HVAC systems is an under-recognized problem. The authors have worked on three buildings with this problem in the Midwest within the last few years. Failures found in two of the buildings occurred during construction and in the third building, five years after completion. The copper tubes were wrapped with an elastomeric PVC/nitrile insulation and joined together by brazing at high temperatures to create risers that circulate water from floor to floor. The EAC failures were determined to be the result of a combination of high residual stresses in the copper tubes from the manufacturing process, exposure to moisture on the exterior of the tubes, and exposure to harmful EAC-promoting chemicals, including ammonium and nitrate, inherent within the as-constructed system. Results of on-site investigations and laboratory testing using a variety of physical and chemical techniques and a review of the pertinent literature will be presented.

Subject
Risers, Environmental cracking, Buildings, Water, Insulation, Brazing, Tubes, Corrosion cracking, Joints, Ammonium, Corrosion products, Copper, Residual stress
Keywords:
Environmentally Assisted Cracking, copper tubing, nitrile insulation, ASTM B88 copper tubing
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2014
Association for Materials Protection and Performance (AMPP)
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