Selection of main materials for high- and low-temperature water heaters in the process package of the Northwest Institute

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This is my first time dealing with gasification units, and we are also using the multi-feed slurry process package developed by the Northwest Research Institute. However, in the equipment data sheets they provided, the choice of materials for some of the equipment is indeed quite strange. For example, high-temperature water heaters and low-temperature water heaters. In their data sheet, the material used for the main body of the equipment (housing, cover) is 0Cr18Ni9 or carbon steel + 316L, but the material for the internal components is 0Cr18Ni9. In terms of the media used in these two devices, both are gray water and flash vapor. From a corrosion resistance perspective, if it is feasible to use 0Cr18Ni9 for all the main components, then why is 316L necessary when composite plates are used? Moreover, in the structural diagram, the baffle at the black water inlet is required to be made of 316, and the pipe fittings themselves need a corrosion-resistant lining or a chromium carbide coating. Is it the case that for these two devices, the main issue is not corrosion resistance but rather wear resistance? If a chromium carbide coating is used, does this also mean welding a coating on the inner surface of the stainless steel? Are there any requirements regarding the thickness of such a coating? Moreover, at least three different stainless steel grades are used in one device. Since I don’t have much experience with gasification units, could everyone take a look and see if this material selection is appropriate? Or have you all encountered such material selection issues during the design process?