Reactor vessels for high temperature, high pressure hydrogen services such as hydrocracking, hydrodesulfurizing, and coal conversion, have internal attachments as shown in Fig. 1. Cr-Mo steel base metal is covered by stainless steel suitable for the environment in the reactor. For hydrocracking and hydrodesulfurizing, Type 347 stainless steel is favored due to its better resistance to polythionic acid corrosion1 . In order to maintain an effective thickness of the stainless steel, an approximately 5/16 inch thick double layer weld overlay is applied. A first layer of Type 309 alloy is usually applied followed by a second layer of Type 347 material. Internal rings and pedestals which support trays, beams, and baskets are attached by welding to the overlaid surface. Type 321 stainless steel internals welded by Type 347 filler metal are commonly used in hydrocracking and hydrodesulfurizing reactors.

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