1944-01-01

STAINLESS STEELS - Hot and Otherwise 440151

AIRCRAFT exhaust systems must be designed to withstand service conditions that include severe vibrations, high temperatures from the hot exhaust gases passing along the inside of the pipes at relatively high velocities, while the outside of the pipe system may be subjected to rain and sea atmosphere.
These extreme conditions of operation led to difficulties in the application of stainless steel to the exhaust system.
Failures caused by intergranular corrosion from carbide precipitation need no longer be feared when properly stabilized 18-8 stainless steel is used.
Stainless steel can be stabilized with either titanium or columbium, the cheaper and more easily worked titanium-type steel being satisfactory for most installations, although there are applications where the columbium type must be used because of its higher yield and tensile strengths.
This improved stainless, however has not solved the problem of corrosion at high temperatures in the presence of zinc. Zinc, as bits from drop hammer dies, plating, or in any other form, should be kept away from stainless steel at elevated temperatures.
Another problem that is sometimes annoying is the cracking of welds in thin stainless sheets such as are used in exhaust systems. Rigid control of the composition of the welding flux has been found to eliminate this trouble.

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