Earthing across flanges

[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