This looks like an excellent application for 'Dry Ice Blasting', which is essentially 'sandblasting' done with a different medium. For cleaning fouled surfaces and/or for preparing new surfaces for bonding or coating, there is a surprisingly large range of related technologies and materials, everything from near-diamond to soft like walnut shells. Dry Ice offers great advantages of leaving no solid residue itself, and being relatively mild on the underlying surfaces, while also having the extra boost of wedging slightly under the grime as a solid and then vigorously expanding, providing extra lifting action.

Applying this to rail seems like a great idea, since the weight and mass of the apparatus is not really a problem in that situation.

Cool stuff!