Can S/S B8 studs and S/S SA194 Nuts be used on Carbon steel A105 Flanges ?

[Greg80]

Can S/S B8 studs and S/S SA194 Nuts be used on Carbon steel A105 Flanges ?
I have an application that the external environment is corrosive and from experience the Studs and nuts are always corroded after few months. However the flanges don't corrode because they are painted with special painting resisting to the environment.

So I would like to use S/S studs and nuts on C/S flanges. Anyone has any idea if it can cause any problem ?

Thank you

 

[SnTMan]

Greg80, one potential problem is that the COTE is greater for the bolting than the flange materials, could lead to loss of bolt load in operation, depending on operating temps, gasket characteristics, etc, etc.

B7 can be plated aand or coated.

Regards,

Mike

 

[Greg80]

We used B7 zinc plated and they rust

 

[SnTMan]

HDG works better, but off the shelf class 2 fits are a problem. There are probably some better plating / coatings than zinc, but I can't recommend anything specific.

I don't know of any reason you CAN'T use stainless.

Regards,

Mike

 

[NBrink]

If the flanges were designed for B7 studs, it is possible you won't be able to get sufficient preload from the B8s. Also, as previously mentioned, if you are operating at elevated temperature (I'm assuming you're not operating too hot given that the flanges are painted) the B8s will lose preload on CS flanges due to greater thermal expansion.

Plus stainless hardware is just a massive pain in general...

What is the external environment that's so corrosive?

I've seen PTFE coated studs, liberally lubricated, used to good effect around cooling towers and the like.

 

[CoryPad]

You should try zinc rich coatings like Magni, Doerken Delta Protekt, Atotech Zintek or NOF Geomet. These have much higher corrosion resistance than electroplated zinc.

 

[XL83NL]

Nut embedment (under the nut, to the C/S flange) may cause local damage to the paint on the C/S flange. Is it possible this small area can give potential for galvanic corrosion?

PTFE coated bolts should not be used as a means of corrosion protection. They are merely designed to lower friction.

 

[weldstan]

Recommend B6X (12 CR) alloy bolts with 6 or 6F nuts.

 

[MJCronin]

Consider XYLAN or similar PTFE coated carbon steel bolts.

They have been specified by chemical plants for decades now.... some companies swear by them.

http://www.eng-tips.com/viewthread.cfm?qid=325662

MJCronin
Sr. Process Engineer