Long-Life Heat Transport Loop Material Test 911365

In 1979, a test was initiated to evaluate the use of dissimilar metals in close conjunction with each other, including aluminum, stainless steel and an Al-Ti-Al laminate heat exchanger, in a closed deoxygenated water coolant loop over an extended vehicle life. The closed, sealed loop contained distilled, deoxygenated water initially supplied at <0.3 ppm by weight dissolved oxygen. The system involved a variety of dissimilar metals, including 300 series CRES, 6061 aluminum alloy, gold-nickel braze alloy and thermometer bi-metallics. Coatings were also used to provide added protection to the aluminum. A stainless steel to aluminum transition tube was sandblasted, passivated, alodined and coated with P.D. George epoxy coating No. 923. The heat exchanger was of plate fin construction with parting sheets made of an Al-Ti-Al laminate designed to prevent through wall pitting in case corrosion attack initiated. The test plan originally called for water samples to be collected periodically over three years at which time the test apparatus was to be disassembled for inspection. Favorable analysis of water samples and no evidence of filter obstruction from corrosion by-products delayed disassembly and prompted continuation of the test. The system experienced a total of approximately 10 years of operation. The system was then disassembled and visually/metallographically inspected. This paper presents a detailed description of the test system, test procedures and test results.