Grounding Lugs on Return Cooling Water Piping

[SM.EIT]

Hello Experts,

First of all, my apologies if this belongs in the wrong thread; I feel like it borders between Mechanical and Electrical.

I'm a long time reader and usually am able to find my answers searching through these forums but I have looked everywhere and haven't found any useful info so I'm hoping someone may be able to help me out here.

I'm working on a project where several hundred feet of 24" A106-B Cooling Water Piping is being replaced due to soil/air interface corrosion. Some of the wasted pipe runs just below/adjacent to a T&D cable tray conveying high voltage cables. The piping is fitted with a thin welded pad and three identical grounding lugs welded on top of that plate. My guess is that because of the proximity to the cable tray, the original designer was concerned about a voltage being induced on the pipe from the cables and placed the grounding lugs to prevent any static charge build up.

My issue is that I've read about grounding requirements for equipment but I can't find anything in the Owner's standards or in relevant Code that talks about requirements for grounding pipe. Hoping someone can provide me any info that'll send me in the right direction.

Picture of the lugs here:

http://files.engineering.com/getfil...35-acb5-c4b936b988a6&file=20180329_143553.jpg

Thank you,

SMEIT

 

[LittleInch]

I'm a little confused by this?

Is this pie buried or part buried or??

Has it got an electrically insulating coating?

If the cable is armoured, then there should be no interference or induced current - you only get that from bare overhead wires normally.

I'm just not sure really what your question is?
Pipe earthing on racks is part of the earthing design.
You don't normally earth buried pipes, partly because they often have CP and also there is no reason

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

 

[SM.EIT]

Hi LittleInch - thanks for your response. There's an entire circuit of pipes installed some (this one included) are partly buried, though, not by design. However, the lines run in very close proximity to the ground. There's no insulating coating either and I am 99.99% certain the cables are armoured.

My question was: are there any code requirements for electrical grounding of pipe, if so, which code? I haven't been able to find one that covers this topic.

Thank you.

 

[LittleInch]

It's really an electrical issue, not a pipe code or design issue and to me seems to depend a lot on the designer. Some plants you can't move for earthing strips and rods, others they just earth the main structure and assume everything flows through that.

pipe is generally pretty good about transmitting electrical charge to the nearest point through welded or bolted connections so you don't normally get a static charge.

I guess there was a reason why these things are there, but probably lost in the mists of time and based on some premise which may no longer be applicable.

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

 

[dik]

We often weld stainless steel welding lugs to frames, etc. and even HDG the frames. The lugs are often threaded for NEMA 2 connectors.

Dik

 

[bimr]

"No special grounding requirements are necessary for metal piping systems when they are continuous, and therefore, part of the installation considered as properly grounded."

Classifying Explosion Prone Areas for the Petroleum, Chemical and Related

Cable Trays

 

[SM.EIT]

Thanks for the input from everyone.

I guess I'll never know why these were required.

 

[bimr]

The plate look like a bonding plate. Bonding is used to connect various pieces of equipment together so that there is no potential voltage between the various components.

You have not stated what wires are connected to it.

If the wires are in trays, is it possible that the trays are not continuous? If so, perhaps the trays are being bonded together.

 

[KevinNZ]

On our power station projects there is an earth matt under the whole station. Pipe is connected the earth grid with an earth wire attached to the pipe shoes. Above ground pipelines running way from the station has an earth wire buried next to the pipeline with connecting straps from the pipe shoes.

This earthing is to prevent voltage levels between the steel pipe and the ground.

This can be over kill. Station fault levels and ground resistance can be studied. Often the piping shoe-support-foundation provides enough earthing .

AS/NZS 4853 covers this.

 

[dik]

In some switchyards I've been involved with, if the platform for the equipment is not at the equipment 'ground' and is to the earth type ground, the potential between the platform and the equipment can be several hundred volts. For that reason, your platform ground should be to your equipment ground.

Dik

 

[SM.EIT]

bimr, the wires attached to the posts are connected to the earth grid. The plate was used to allow for a tapping connection between the plate and copper posts since we don't have a welding procedure for copper. The cable tray runs overhead the piping so there isn't any physical connection between the two.

KevinNZ, I agree that it seems like overkill and a pipeshoe (of which there are many) would be a more ideal location for attaching a ground wire to. I was thinking maybe it's because all of our pipe shoes rest on concrete sleeper blocks which would insulate itself from the ground but that wouldn't have any affect on the path of the electrons through the grounding wire. And thanks for the reference! I would like to better understand the reasoning behind why this may have been required.

Thanks again everyone for your input.