Stainless steel flanges with carbon based bolts

[emanoelman]

I have a doubt, can it be used stainless steel flange, with carbon bolts?
On the plant that I'm currently working, WNRF flanges A/SA 182 are connected with B7 bolts. Is it allowed by ASME connections of different types of materials? Will it increase corrotion rate?

 

[metengr]

Your doubt is well founded. There could be corrosion issues if the B7 steel flange bolts are located in a wet environment, where galvanic corrosion can occur. Compounding the problem with corrosion could be hydrogen assisted cracking of the B7 bolting.

Second, clamping load for this joint design must be carefully evaluated based on service temperature.
Material choices for bolting is up to the design engineer because this is a process detail, and is not covered by Codes and Standards. Codes and Standards do provide necessary information for allowable stress values and some basic exemptions for use.

 

[CoryPad]

You may have different thermal expansion coefficients, which can lead to excessively high bolt stresses.

 

[emanoelman]

Thank you for clearing of this item.

 

[rneill]

Despite the potential problems, the use of B7 bolts with stainless steel piping in near ambient temperature dry applications is relatively common. For example, the Process Industry Practices (PIP) piping line classes for SS specify B7 bolting.

 

[rmw]

So, are the naysayers in this thread recommending the use of B8 bolting with SS flanges? We manufacture a large SS vessel that we use B7 bolting for on all the flanges, some as large as 3 inch and others that I can walk through with a hard hat on. I am not saying because we do it that makes it right, just that it is what we do.

rmw

 

[SJones]

No. They are not making a blanket recommendation for B8 fasteners. Like most materials issues, they are pointing out that there is a risk associated with having the carbon steel - stainless steel couple and some of the considerations that have to be made to deal with those risks.

Steve Jones
Materials & Corrosion Engineer

http://www.oilandgaspeople.com/cv/11499664

http://www.linkedin.com/pub/8/83b/b04

 

[emanoelman]

OK, I agree that B7 can be used with SS flanges, but in my case, it will be used outdoor, so there will be large ammount of humidity, and it is also used for natural gas pipeline flanges. I am still for the solution of usage of SS bolts.

 

[rneill]

I don't think humidity is necessarily a problem. The B7 would really need to be "wet" such that there was electrolyte (conductive fluid) physically connecting the B7 bolts to the SS flanges.

 

[TVP]

Since this is an outdoor application, are the B7 bolts coated? If so, what type of coating? Where is this facility located? If there is constant exposure to rain or this is located near an ocean, I would use stainless steel fasteners.

 

[rmw]

Our B7 bolting is zinc plated. This thread has been eye opening. I am dealing with some serious galvanic issues elsewhere in our process, but had never given a moment's thought to the external bolting (SS to SS flanges or SS attachments). And, our product can and does go into marine environments.

Oddly enough, we started out with B8 bolting and switched to B7.

Thanks for all that contributed.

rmw

 

[rneill]

Just a word of warning regarding the B8 bolting. There are two classes available, Class 1 and Class 2. The Class 2 is strain hardened and is considered medium strength. The Class 1 is not strain hardened.

With Class 1 you need to consider whether the bolting has sufficient strength for your bolted connection (and there are limitations in ASME B16.5 around where low strength bolting is permitted).

With Class 2 you may need to consider the service environment and whether a strain hardened bolt is acceptable (e.g., may be more susceptible to some failure modes).

 

[strider6]

have you considered to use an insulating kit like this:

http://www.pikotek.com/product_techdata/Insulating Kit Product Brochure.pdf

S

Corrosion & Rust Prevention Control

 

[SnTMan]

The other side of CoryPad's coin is that B7 bolting with SS flanges can mitigate loss of bolt load at operating temperatures. If the bolting is not subject to unusually corrosive conditions, I would much prefer B7.

Regards,

Mike

 

[unclesyd]

Talked to my bolt buddy today and aside from the supplying B7 for SS flanges he has to large accounts that use B7M Blue Teflon and 2HM Blue Teflon for offshore applications. He also stated that he is supplying a lot of A453 660B for similar applications.

All our outside SS Flanges we use B8 or B8 Class 2. We are situated on a salt water bay. We use C5A or FelPro Cu based thread lubricant on all fasteners. On any flanges above 650°F we use a BN lubricant with any fastener material.