Air conditioner failure investigation-intergranular cracking in a pure copper condenser tube
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A failure of a 7 1/2-year-old commercial rooftop air conditioning system was investigated. The systematic failure analysis procedure and eventual discovery of a leak in a pure copper condenser coil are discussed. Severe denting of several tubes, including the tube that leaked, was discovered in the area of the steel tube sheet. A metallurgical examination, including scanning electron microscopy, revealed intergranular cracking, a process that is common among some copper alloys suffering from stress-corrosion cracking but is rarely observed in pure copper. Research of available literature is presented, and the conditions under which pure copper may exhibit intergranular cracking are discussed. Also presented are vibration measurements of the air conditioner taken during operation, which rule out operating loads as the cause of the tube denting and eventual cracking. The cause of the denting remains unknown. However, the denting probably occurred during manufacturing, and the high stresses associated with the dents, in the presence of corrosion, resulted in intergranular cracking and eventual leaking.
Keywordsintergranular cracking pure copper condenser tube stress-corrosion cracking tube denting
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- 1.“Corrosion of Copper and Copper Alloys,” Corrosion, Vol. 13, Metals Handbook, 9th ed., N.W. Polan, ed., ASM International, Metals Park, OH, 1987, pp. 614–16.Google Scholar
- 2.“Stress-Corrosion Cracking,” ASM Specialty Handbook: Copper and Copper Alloys, J.R. Davis, ed., ASM International, Materials Park, OH, 2001, pp. 419–29.Google Scholar
- 6.“Stress Corrosion Cracking Control Measures,” NBS Monograph 156, National Bureau of Standards, U.S. Department of Standards, June 1977.Google Scholar
- 7.“Standard Test Methods for Detection of Cuprous Oxide (Hydrogen Embrittlement Susceptibility) in Copper,” B 577, ASTM International, W. Conshohocken, PA.Google Scholar
- 8.“Standard Specification for Seamless Copper Tube for Air Conditioning and Refrigeration Field Service,” B 280, ASTM International, W. Conshohocken, PA.Google Scholar
- 9.J. Berry: Proven Method for Specifying Spectral Band Alarm Levels and Frequencies Using Today’s Predictive Maintenance Software Systems, Technical Associates of Charlotte, Charlotte, NC, 1990.Google Scholar