Metal loss caused by selective leaching of aluminum (referred to herein as dealloying) in certain aluminum-bronze (Al-Brz) alloys is an environmentally-induced degradation mechanism in piping systems containing cast components exposed to marine, brackish, or raw water service. Examples of this form of degradation have been observed in ASME Code Class 3 Essential Cooling Water systems. Mechanical properties for tensile strength and fracture toughness of Al-Brz static and centrifugal castings, fabricated to ASME SB-148 CA952 and CA954 specifications, can locally degrade in service due to dealloying under long exposure to aggressive water environments.
This paper presents the results on the reduction in mechanical strength as a result of dealloying. A mechanical testing program was completed where 20 tensile and 22 fracture toughness specimens were tested to determine the reduction in mechanical properties from no dealloying (virgin condition) to various amounts of dealloying up to 100% dealloyed condition measured across the specimen. The specimens were fabricated from components removed from service (some components being in service for over 25 years). The data were plotted as a function of percent dealloying where a systematic decrease in properties was seen directly dependent the amount of dealloyed material in the cross-section of the specimen.