Chris they use this method on large tanks....not sure what code it follows, but I've heard that is has been used sucessfully to find leaks in large tanks or weldments that have to hold liquid. Dusting flour along the backside of the joint as a developer and any leak will show up as the flour will stick to and absorb the diesel fuel.
I'm sure others who use this method can chime in and give us more info. I've only heard about it being done, I've never actually used it.