Bolt selection for stainless steel lugged valve 1

[p6g2p6]

Hi,
I am looking to install a lugged butterfly valve with a 316SS body. I'm trying to decide if I should use B7 or B8 (class 2) Hex bolts for this application. The flanges are also 316SS. My concerns with using B8 bolts are the lower strength, and the risk of galling (even if using a anti-seize). They're also not cheap. My concern with using B7 bolts is the risk of galvanic corrosion occurring between the valve body and bolts, since there will be direct contact at the threads.
Does anyone have any experience with stainless lugged body valves? Do you think I'd be fine using B7 bolts if we use a lubricant?
Any input would be greatly appreciated.
Thanks.

 

[GBTorpenhow]

For tapped holes, use hex cap screws, not hex bolts.

I would not use B7 with a stainless valve/flange for galvanic corrosion reasons. Differential thermal expansion could possibly be an issue as well depending on the joint geometry and temperatures expected.

Yes, B8 or B8M Class 2 cap screws are expensive. Depending on your valve size, pressure class, thread engagement, and gasket stress requirements you might be ok with Class 1 screws.

 

[p6g2p6]

Thank you for your input. I'm still waiting to hear back from the gasket supplier, so that I can determine if class 1 screws will suffice for this application. I always hear mixed opinions on using stainless screws with stainless tapped holes, so I wanted to see what people thought about it on here.

 

[EdStainless]

If the temperature is suitable, I have seen people using coated (fluoropolymer) steel fasteners in SS hardware.
Not my favorite but looks to work.
The other option to minimize galling is to use 2205 bolts, again if the temp will allow.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

Is the valve exposed to water or not on the outside?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[p6g2p6]

Littleinch, it’s in a valve shed, so it’s not going to get rained on or submerged in water, but it is a damp environment. There’s typically a couple inches of water on the floor (not higher enough to touch the valve).

 

[Krausen]

B7 studs with two heavy hex 2H nuts (instead of cap screw). Ive never had issues, but I work mostly in drier, desert environments. Yet I’ve seen same practice in more humid environments with same success

 

[TugboatEng]

You have described a wet environment. You will have galvanic corrosion.

B7 will probably work for some time but is going to make maintenance very difficult.

If you're so concerned about strength and galling there are quite a few fastener options. Bumax has a portfolio of high strength SS fasteners and they're widely used enough that their prices are reasonable. You can buy Bumax 88 through McMaster-Carr. You may also consider helical inserts in the valve body.

 

[SJones]

B7 with ZnNi electroplate. Job done. Standard offshore application for one or two operators.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[r6155]

For tapped holes, use STUDS, not hex bolts.

Regards

 

[TugboatEng]

You can go either way. Studs can be easily cut and renewed if a nut seizes.