Results of XRF analysis and historic literature on materials and construction of aircraft engine exhausts are posted for whom it may concern. Exhaust system materials must be weldable. Exhaust systems are subject to gases at up to 1,000 degrees C with open stub exhaust metal heating to 400 degrees C and collector ring exhaust metal heating up to 800 degrees C. Pulsing of exhaust and back pressure waves can cause ‘panting’ and fatigue failure of metal. Too much overhang can cause a stub to detach. Expansion of hot metal and differential expansion of dissimilar metals can cause weld fractures. High moisture and combustion by products can cause corrosion of metal. All these factors figure in material selection.
Below are analyses of various material solutions. Original designers did not factor operation beyond 5 years. Operation of historic aircraft will require continual replacement of exhaust systems. These notes are provided to assist in material selection and understanding of design factors. Wartime design factors such as flame damping at night, suppression of vapour trails during daylight and harnessing exhaust thrust for increases in speed are equally important to appreciate the final architecture of the design. Also relevant are wartime shortages of critical alloys such as nickel in material selection. Modern operators may refer to the analysis of postwar Inconel and titanium stabilized 18-8 ‘Staybrite’ RAAF Mosquito Packard Merlin exhaust stubs below for guidance in material selection pathways today.
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By: powerandpassion - 23rd November 2016 at 10:49
The Nickel Bulletin Vol 4, Jan 1931 describes the British patent granted to F Krupp AG for “Titanium and Vanadium additions to Nickel Chromium Steels for the Prevention of Weld Decay.” So it seem this alloy technology was developed by Krupps in Germany and would made its way out into the world via licencing to other firms and nations. No doubt German aircraft exhaust metallurgy would reflect this, but I have to find some old pieces of Luftwaffe exhaust to test this.
Out of curiosity the 1925 Department of Mines Bulletin from New South Wales, Australia, describes Chromium, Cobalt, Nickel Titanium and other mineral deposits, with Rutile being a natural oxide of Titanium. So certainly by 1925 there is interest in this material. The Bulletin describes Nickel as being an ‘important alloy in aircraft steels’, so the Australian prospector was not naive in 1925. Today Australia supplies about 40% of the world’s rutile, sourced from sand mining. So keep an eye on who buys up the all sand mining companies, when commodity markets are down….
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August 7, 2016 at 8:14 am