Waterjet Cleaning for Coating Removal 3

[sxz]

If high pressure water jet, 40 k psi, is used to clean the coating inside crude oil storage tank, the metal yield stress is 36 k psi, does this high pressure cleaning affect the weld/metal hardness (say 225 HBN after welding)? does the tank weld hardness have to be maintained the same after welding?

Thanks for your inputs.

 

[fegenbush]

I do not think that pressurized water cleaning will affect the hardness of the steel or welds for carbon or low alloy steels. Any increase in hardness would be offset by the erosion of the top layer of material.

 

[JStephen]

I assumed that the pressure involved with the water jet is the pressure prior to it going through a nozzle, and has no relation to forces at the steel surface.

But note that in normal sandblasting, the abrasive used is harder than the steel with no ill effects.

 

[Duwe6]

That steel is not work-hardenable to any significant extent, so hardening cannot happen. And I think that water does not have the impact properties of shot-blasting with chilled steel shot. You can change the surface properties with shot-blasting, on hardenable steels. It would be interseting to check the after-hydroblast surface hardness of a work-hardening alloy, though.

 

[Airsmybag]

For work hardening or stress alteration to occur, the molecular structure at the surface of the steel would need to be disturbed as by abrasive or shot impact. At 40,000 PSI (nozzle presure) water will remove coatings and most rust, but will not effect surface structure. In abrasive blasting, we consider the fact that the abrasive hardness must exceed the hardness of the surface to be removed. IE: walnut shell will not remove tightly bonded rust. An analogy I use is that you cannot cut a copper pipe with a plastic knife. We use abrasives with different hardness and shape to produce different surface profiles or surface effects.

airsmybag