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An arsenical admiralty brass (UNS C44300) finned tube in a generator air cooler unit at a hydroelectric power station failed. The unit had been in operation for approximately 49,000 h. Stereomicroscopic examination revealed two small transverse cracks that were within a few millimeters of the tube end, with one being a through-wall crack. Metallographic examination of sections containing the cracks showed branching secondary cracks and a transgranular cracking mode. The cracks appeared to initiate in pits. EDS analysis of a friable deposit found on the inside diameter of the tube and XRD analysis of crystalline compounds in the deposit indicated the possible presence of ammonia. Failure was attributed to stress-corrosion cracking resulting from ammonia in the cooling water. It was recommended that an alternate tube material, such as a 70Cu-30Ni alloy or a titanium alloy, be used.

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