Direct contact between SS and CS material

[rapid1348]

What is a good engineering practice to avoid direct contact between a stainless steel pipe with stub end connection and carbon steel lap joint flange ? Will painting the lap joint flange suffice?

My second question :To bolt up two stainless steel flanges with CS stud bolts and nuts ,what is the good practice to avoid the direct contact between the nuts and flange back side.

Regards
RezaMani

 

[unclesyd]

You can purchase an isolation kit from you gasket supplier that contains all the necessary components to electrically isolate the two flanges.

Is there a real need to isolate the flanges as isolation of flanges adds to maintenance problems.

 

[ceobob]

Rezamani,

Had similar problem.

Please try and obtain NACE RP 289 on isolation joints.

Any proposed bolting should be isolated. Resistivity measurements will verify if you have successful isolatiion.

 

[rapid1348]

Thank you unclesyd ,

We r not going to isolate two mating flanges but to isolate the ss stub-end piece from the cs lap joint type flange.Gaskets are generally used for isolation of two mating flanges and actually we have the gaskets in between the two stub ends.
I hope that I could understand your point and explain mines clearly.

Cheers

 

[ceobob]

Meant to say NACE RP286

Summary can be found from following link

http://www.nace.org/nacestore/assets/freestandardsreports/RP028602.pdf

 

[Metalguy]

You can insert all the gaskets you want, but IF each side of the joint is supported by hangers of some kind, you may still have a problem. Be sure to use an ohmeter across the joint to check if you REALLY have them isolated.

 

[stanier]

Providing that them interface is dry you dont need to provide isolation. You need an electrolyte before corrosion takes place. There are plenty of installations around with backing flanges behind stainless steel stub ends withio=out any treatment. If you were in a wet environment such as a sewage pumping station, in the Andes, or subsea, yes , you would need to do something but otherwise no.

 

[rapid1348]

ThANKS EVERYBODY FOR YOUR GUIDANCES.I WILL FOLLOW THE NACE STANDARDS.