A metallurgical failure analysis was conducted to determine the cause of cracking in several sections of copper refrigeration tubing. The tubing in question was part of a new mechanical design, implemented to mitigate fatigue failures of solder joints that had occurred in tubing systems fabricated under the previous design. A comprehensive metallurgical evaluation revealed intergranular fracture of the copper in a region of the tubing that had been significantly cold worked during manufacture. On discovery of a source of moist ammonia in the system, associated with the location of failure, intergranular stress-corrosion cracking (SCC) was identified as the failure mechanism. A modified design, incorporating annealing of the formed copper tube section, was recommended to avoid future failures.
