Static Bonding across dissimilar metal flanges 3

[Bazinga]

Hi everyone, does anyone know best practice for static bonding across carbon steel / stainless steel flange interfaces where an insulating gasket is used? The point of the insulating gasket is to electro-chemically isolated between the two flanges and avoid any galvanic corrosion. However one of the electrical engineers raised concerns about a loss of continuity in the grounding path and questioned whether we should put a jumper cable across the two flanges. Has anyone come across this before? I've checked a few guidelines including NFPA 77 and couldn't find anything conclusive in there.

 

[pierreick]

Hi,
Your electrician is 100% right. You must install a bridge (jumper cable) for continuity's sake(earthing).

https://www.brymec.com/earth-strap-continuity-connectors-100mm.html

BTW, it's the same between flowmeter and piping.

note: Very weird to use different metallurgy, poor design!
Pierre

 

[SJones]

Note the “electro” in electrochemical. There still needs to be normal electrical isolation.

https://www.phoenixcontact.com/en-gb/products/surge-protection/isolating-spark-gap

Just one of the reasons why insulating flanges in convoluted piping systems are a bit of a nightmare.

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.

 

[Bazinga]

So putting this jumper cable on isn't reintroducing a risk of galvanic corrosion between the two flanges? This is a carbon steel / stainless steel interface.

 

[SJones]

Define the specific arrangement for a "jumper cable" in terms of maintaining the electrical isolation between the two sides of the flange, and see the reply above. The need for isolation in the first place should also be re-examined. External issues can be addressed by painting, for example. The internal environment may also not create an undue corrosion risk.

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.

 

[LittleInch]

There are two things here.

The first is whether there is a risk of galvanic corrosion or not. If the amount of stl steel compared to carbon steel in the system is small then probably not. You also need some sort of conductive fluid. Some companies just seem to impose a blanket rule which doesn't always make sense. Why are you doing it in the first place?

If there is a reason to electrically isolate the two materials, jumping it with a cable instantly obliterates your expensive isolation kit.

Your electrician clearly doesn't know anything about galvanic corrosion and is just looking at this as an earthing problem as is Pierre I believe.

If this is just one valve then I wouldn't bother, but if you have two separate large masses of Stl Stl and C Steel then my guess is you need to have two separate earthing systems which are not connected, except via earth and connect the two via one of those surge protectors which allows pass through of high voltage spikes, but not the low volage galvanic stuff.



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

 

[pierreick]

Hi,
Yes, I do believe this is a safety hazard, lack of earthing! Definitely not using the same piping material is a mistake as explained above by experts.
As long as the pipes are already in place, the story about corrosion is of second order, just $. Fire or explosion is the real problem.
My view only
Pierre

 

[IRstuff]

Just to clarify; a jumper does not re-introduce galvanic corrosion to the flanges, does it? There maybe galvanic corrosion between the jumper itself and one or more of the flanges if there's a material mismatch, but if the flanges are still separated by the insulator, there shouldn't be corrosion between the flanges?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[TugboatEng]

There shouldn't be corrosion between the flanges because their surfaces will be protected by the gasket. There will be corrosion in the piping immediately adjacent to the stainless flange.

 

[GBTorpenhow]

If you bond across the joint and electrically connect the two sides of the flange pair, you just defeated the purpose of the flange isolation kit.

If you absolutely need the isolation and still want to have a safe path to ground then you could look at a spark gap arrestor or overvoltage protector. These are usually used in situations where a cathodically protected underground pipeline system needs to be electrically separated from a grounded above grade piping system, but for safety reasons it would not be acceptable to have an appreciable voltage difference across the flange pair.

There are several versions of this with different uses but in short it installs across the flange pair and will keep small voltages from passing through but will allow large voltages through.

 

[1503-44]

Do you want a pipeline spark gap?

https://process-technology-online.com/plant-processing/isolating-spark-gap-forpipeline-flanges/

https://www.phoenixcontact.com/en-us/products/surge-protection/isolating-spark-gap

https://www.pipeline-journal.net/ar...itable-spark-gaps-and-evaluation-installation

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EdStainless]

Are you wanting to connect for static discharge or for electrical grounding?
IF you connect to ground then you have no isolation.
Static can be dissipated through fairly high resistance connections, and you can maintain galvanic isolation if you do it right.

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

 

[hacksaw]

Don't forget the flange bolting does provide a degree of electrical continuity.

 

[GBTorpenhow]

Don't forget the flange bolting does provide a degree of electrical continuity.

The insulating gasket kit includes dielectric washers and bolt sleeves to prevent this.

 

[hacksaw]

As raised in an earloer comment, the fluid composition and its conductivity is an essential bit of information that is lacking in the problem posed by the OP.