Passivation and Surface Finish - do you need a min. finish to passivate 316 2

[65CCJ]

I have fittings with 1.5" long 1/4 OD tubing ends with drilled ID to .13" The drilled finish is maybe a 250Ra. The drawings call out 63 Ra everywhere. I bought the parts off as this is just for flow and won't affect flow performance significantly. Our QC engineer is having a fit saying the surface finish is too rough to passivate. Its just cleaning iron from surface so why would roughness matter> Does it matter? Can anyone enlighten me on why it would? Thank You.

CJ

The attached file shows picture of ID of part

 

[bcd]

Stainless steel castings are passivated with as cast surface finish. Passivation should be done in accordance with a standard to get consistent results. Refer to the standard for any surface finish requirements.

 

[EdStainless]

It will impact flow, but there are not many of these then likely you won't see it.
Someone must have worked hard to make them this rough.
Passivation does not care about surface finish.
Toss them into warm 40% nitric acid and it will work.
I have seen people pickle rough finishes to remove sharp points and burrs.

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P.E. Metallurgy, consulting work welcomed

 

[BiPolarMoment]

Someone must have worked hard to make them this rough.

"As Machined"

 

[EdStainless]

I should add that the torn and smeared metal does hurt corrosion resistance.
They have created crevices which will initiate corrosion much easier than a smooth bold surface.
In most piping systems there are so many other crevices formed that it usually doesn't matter.
But it is very poor form.
You can't just reject them?

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P.E. Metallurgy, consulting work welcomed

 

Passivation does not care about surface finish.

I'm not qualified to dispute that, but surely better surface finish would help with subsequent inspection? Because an operation doesn't happen unless and until it passes inspection.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

Maybe I was a little extreme in that but having worked with castings and pickled surfaces I have never seen an issue related to roughness.
This case is a bit different.
The possible concern in this case is that they have created laps and smears that may have created areas that are not open to the surface.
In that case you wouldn't get passivation.
But much worse is that you have created a crevice corrosion initiation site.
My concern here isn't related to passivation but just simply corrosion resistance.

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P.E. Metallurgy, consulting work welcomed

 

[BiPolarMoment]

My concern here isn't related to passivation but just simply corrosion resistance.

As you said earlier :

You can't just reject them?

I'd be very wary of any supplier/internal shop providing me parts that looked like that, regardless of if they meet print. Looks like a garage job; does no one own a reamer that can clean that up?

 

[EdStainless]

Can't he even be bothered to sharpen a drill bit?

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P.E. Metallurgy, consulting work welcomed

 

[65CCJ]

They are going to burnish ID back to 63 Ra as was called out on print. We own the shop so its not a problem.

 

[65CCJ]

There is a strict cleaning requirement I'm not familiar with once parts are complete and welded together.

 

[EdStainless]

You say burnish, I hope that you don't truly mean burnish.
If they did a real burnish all that they would do is smear the surface to make it look smoother.
This needs to be reamed or have some other cutting operation performed.

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P.E. Metallurgy, consulting work welcomed

 

[BiPolarMoment]

If they did a real burnish all that they would do is smear the surface to make it look smoother.

I was thinking the same thing but since I've heard the nomenclature misused all the time (and I am probably guilty as well) there's good odds they do not mean that literally. Also, if literal that seems like far more complex approach than reaming it.