Problems with metal stains, etc. 1

[Dragon]

To whom it may concern.
I work in the medical device industry as a technician on a hypotube line. As part of my duties I am trying to solve a problem we're having with our passivation plant.
The process involves dipping a bunch of tubes tightly packed together and tied with wire in the following solns:
Pickling soln. containing 5-20% Nitric Acid and 1-7% Hydrofluoric Acid.
Water Rinse.
Cleaning soln. containimg 25-60% Phosphoric Acid and <10% Surfactant.
2 Water rinses.
Nitric Acid soln. containing 71% HNO3.
2 Water rinses.
On inspection afterward on skived sections of tubing, we find black particulate inside.
I would suggest that this may be oil in soln. which gets trapped between the tubes and inside them? During transfer from one tank to another, the bundle is first let run-off over the tank after the pump is turned off.
There is no blow-through over the tank. Any suggestions as to what we're seeing???

 

[Gaz]

What type of alloy are you using?
Some types of non weldable s/steel have too much carbon in them. Could it be carbon, untouched by the acids, that you see?. How big are the particles? How well attached are they?. Is the surfactant correct for this acid?, this could be breaking down to carbon.

 

[Dragon]

Gaz,
The alloy we are using is 304L stainless steel. Carbon content is about .03% C.
The particles seem to be loose and average about 5 microns in size.
Is there any test you know of for hydrocarbons (oil) we could use?
The soln. we are using to clean is a certified cleaner from Anopol so I would presume it would not have any intrasolutionary problems between the acid and the surfactant. Wouldn't make sense to market such a product.
I am going to attempt to sample some of the deposit for SEM analysis which should tell us what elements are present.
If you think of anything else let me know.
Thanks for your help,
Dragon.