charliegk: You should be carefully think out not only the materials of construction for the caustic injection system, but also the design. It is not clear whether you are interested in materials selection for the crude line or for the injection quill or both. The caustic certainly needs to be injected into the crude line with an injection quill that keeps the caustic away from the I.D. of the crude pipe. The injection quill should be nickel 200, based on the temperature, although alloy 600 may also be resistant. At 500F any caustic that concentrates under deposits, in crevices, will probably result in caustic SCC in the presence of an aqueous medium. Nickel 200 is the most resistant material for high temperature caustic. Hope this helps! David Hendrix The Hendrix Group Inc.