We have a proposal for several heat exchangers (some carbon, some Stainless).  The proposed blast material from the vendors is processed river sand.  We asked for flint.  The supplier has a considerable mark-up for this requirement.  I think I know the issues between the two media, but am looking to see what others think.  (I think River sand on the C/S surfaces would be ok, but not on the Stainless surfaces).  Thoughts?