Earthing across flanges

[Lc1]

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With regards to electrical continuity across pipe flanges to bs 7671 I cannot find anything on how to size flat braided cable. Could someone point me in the right direction please is there a rule of thumb with regards to bolt size? Thanks

 

[Pete999]

With regards to electrical continuity across pipe flanges to bs 7671 I cannot find anything on how to size flat braided cable. Could someone point me in the right direction please is there a rule of thumb with regards to bolt size? Thanks

Why would you want to? don't the big bolts form a good enough connection? done any testing.

 

[Lc1]

I think the site has a belts and braces approach. From what I have seen the straps are different across flanges of the same size. Can’t see anything in bs7671 with regards to sizing them?

Thanks

 

[snowhead]

What is carried in the pipe, is it powder of some sort by any chance?

 

[Lc1]

Just water in the pipe.

Thanks

 

[richy3333]

He said flanges

 

[Lucien Nunes]

For what purpose is the pipe being made electrically continuous? WIMES spec, extraneous parts or just because?

 

[LeeH]

I’ve had my head in my hands tying to convince a project engineer that using braided straps across flanges is pointless when it’s full of M20 bolts

Measure the strap with a vernier calliper to get the csa. Or ask the manufacturer.

 

[Pete999]

I think the site has a belts and braces approach. From what I have seen the straps are different across flanges of the same size. Can’t see anything in bs7671 with regards to sizing them?

Thanks

 

[GBDamo]

I worked for many years on chemical plants and bonding across flanges was very randomly (to the uninitiated) applied.

I think its all down to the level of experience of the comical (chemical) engineers.

Straight out of uni = bond everything that doesnt move.

Experienced = bond across non-conductive components. Primarily driven by testing then by knowledge and experience.

Quite often it was the pipe that required bonding between the flanges.

Sometimes it was the flanges but to stop them accumulating a charge.

These kind of decisions should be led by an engineer rather than a spark, they have more knowledge of the material being transferred and the materials of construction of the pipework, it could be lined with plastic or glass.

 

[GBDamo]

I dont think BS7671 will be of any use as this "bonding" is often not forming part of the electrical installation, albeit connected to earth terminals that do form part of the electrical installation, they are there to stop accumulation of static at insulated points within the pipework.

These have been known to discharge and ignite flammable vapours.

 

[snowhead]

What's crazy about it is if the flange bolts are being used to hold the strap then unless the bolts are removed and the flange cleaned up the contact area will be no better with or without the strap.

Best of luck undoing the flange bolts if the pipe has water in it, get some waterproofs.
And if it's a new installation don't let the Pipefitter see you removing the bolts or you'll be removing 1 or more of them from somewhere quite painfull.

 

[PEG]

This is certainly a "why and how" question,for the site engineer.
The circumstances,area and contents of the pipe,may negate the removal of even one bolt,from a sealed flange,and the person responsible for OKing such a move,is the one to explain the reasons for bonding.

I have had this very situation,at a large,Cheshire based refinery,where one of the off-hand,dismissive statements from a post-graduate assistant,to the missing engineer,suggested "if you're that concerned about the integrity of the flange bolts,then just stud-weld a stud,on each face,and strap between them..."

One of the old school plant supervisors,present during this escapade,turned his head towards the young gent,and asked "A stud-welder,son? ... do you know what's in that pipe?..."

 

[snowhead]

The probelm with Refineries is they don't seem to have Little fires.
It's all or nothing..

 

[bomjac]

“Hot-Bolting” is a very common practice in the oil industry, prior to a shutdown or pipe changeout. Basically the pipe fitter will change every bolt in a flange, one by one until they are all swapped out for new. It means that come the shutdown they can change the spool or gasket etc quickly without having to worry about seized bolts. I had guys who spent many days doing this offshore!

To go back to the OP, an easy solution would be to just throw in a serrated washer between the nut and flange on each side of one of the threaded studs. Actually a useful method to ground Motors on skids, rigs or ships when the contractor has forgotten to run an earth cable.

The only reason I can see for bonding them is to prevent static build up where Highly flammable chemicals are used, but mostly if the chemicals are really explosive 5he pipes will be fully welded rather than flanged.but if it’s water - why bother.

I will add that my current employer has procedures that actually allow for welding on live crude lines (must be pressurized and with a certain minimum level of flow) - got to love the Middle East!

 

[PEG]

Yep,the really dangerous work,is in their embassy...

 

[David Prosser]

Why would you want to? don't the big bolts form a good enough connection? done any testing.

Not always,often the big bolts will do very little to aid continuity. The pipes are glass/resin or plastic coated with a non conductive gasket between flanges. Even older pipes are heavily painted and cant be relied on for decent continuity.

Apologise for the picture but I'm not a pipe fitter so don't normally take any pictures of them ! As you can see virtually zero continuity through bolts.

 

[Lc1]

Thanks for all the replies.

 

[Andrew Hunter]

WIMES is driven primeraly by 7671 and this issue is an equipotentil bonding issue.
Had a disagreement with an "Engineer in the past where we used M6 braided earth bonds for bonding tray work. Hes issue was " I dont think them braids are 6mm as they dont look as big as them 6mm G+Y conductors". My response whilst stuffing a Tech specification sheet for said braids was you are quite correct they are not 6 mm braids they are 4mm2 and if you would like to check 7671 the minimium size is ?" (can anyone guess).
I continued with the green and yellow conductors are 6mm2 but dont worry we shall not charge you for the extra 2mm unless of corse you insist on us changing all these bonding braids to 6mm2 G+Y.
Never heard anymore on that subject.
However when bonding across pipe flanges it does tend to be to long a distance for braids so 6mm2 G+Y it is.

 

[StinkyPete]

Somewhere in the back of my mind is a story about an old ABB MagMaster not working because of bonding between flanges and they all had to be removed for the '5-before, 3-after min.' head diameter lengths? Something to do with ABB flow heads needing 'floating' slip-rings between gaskets, between flanges? I remember thinking it was funny as it contradicted what you'd think on bonding.
Maybe I'm recalling this incorrectly.

Still... In the industries I've worked in, on the Scotch-coat types of pipework that David provided a picture of above, the flange is normally drilled, tapped and a 6mm strap bunged in. If deemed necessary.

I agree with the comments above about this being a call for the lead engineer and bonding should be done in the priority order of medium, process, electrical.
Bonding for the sake of bonding is for the over enthusiastic. For me, it come back to the fundamental question of what is bonding for? And if it isn't for this, then it's not for anything.

(Disclaimer: I'm industrial electrical but mainly control. Ignore all of my bitter ramblings above.)

Cheers, SP