removal of carbon contamination of 316 SS?

[QAweasel]

We are currently fabricating a structure from .250 thick 316 stainless. A vendor contracted to form the sheets into channels 4in. X 4in. 10 feet long reportedly used soft(Rc22) carbon steel dies and punches to form said channels. Our drawings specifically state "NO CARBON CONTAMINATION ALLOWED"

The channels were received from the vendor with orange oxidation leaching from the marks left by the forming process. These channels are to be used on an ocean going vessel and this condition is obviously unacceptable.

Question: what if any is the best process for removing the embedded carbon steel particles from the channels? Note: vendor has advised that 360 tons of pressure was required .

 

[JR97]

QAweasel,

The referenced thread may help although it deals with surface not impregnated contamination.

thread1135-155148

 

[QAweasel]

Thanks but we have already tried most available methods including passivation. It would appear as you stated that the particles are impregnated...

 

[unclesyd]

If you have the facilities your best bet will be a HNO3/HF pickling bath and then passivisation with HNO3.

There are some pickling pastes available but are limited in effectiveness for embedded contamination.

 

[kenvlach]

Raising the nitric acid solution temperature to 120-130 [sup]o[/sup]F, as with Types VII & VIII passivation per QQ-P-35C, will speed it up. More fumes, though.

Electropolishing will work, but more expensive.

If making lots of such items, tooling should be either SS or chromium plated.

Make your specification more explicit: "NO CARBON STEEL CONTAMINATION ALLOWED. TOOLING MUST BE CUSTOMER APPROVED."

 

[EdStainless]

Pickle and passivate is the only sure way.
If you don't want the surface dulled or etched then you could try passivation in warm Nitric acid first. We use 20% acid at 130F for about half an hour or longer. Then rinse with tap water followed with a hot DI water rinse.
My guess is that your attempt at passivation was not agressive enough.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm