scalling in graphite tubes

[Sundaravadivel]

Dear Fellow members,

As you all know that graphite heat exchangers are the best for heat tranferring for corrossive fluids. when phosphoric acid is cirulated in the tubes, within a months time it gets scalled heavily and in some cases high choking is there.
what is the way of cleaning the choking of phosphric acid in graphite tubes, mecahnical cleaning will damage the tubes.
in which acid / solvent this Phoshoric acid will dissolve without afftecting the impreganation of the graphite.

sundar

 

[BRT549]

Try a 7% H2SO4 solution - fill your evaporator with pond water or other fairly clean water, then add sulfuric up to the 7%. Heat to 80 C and circulate for about 6 hours.

I am assuming it is a wet-process phos acid plant? What strength is the phos acid? This would work for everything but superphosphoric acid (~69% P2O5).