Major grounding problem... looking for solutions.

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A little background:I'm not a welding engineer, but work for a welding company.  We have been tasked with adapting our equipment to a welding structure that another company has created... and is currently building.  There are alot of issues involved, but one that has me stumped right now is the grounding.Here is the problem:  (see included link to pic)http://s64.photobucket.com/albums/h1...GPROBLEM-1.jpgThe machine/structure has a static floor (does not move) and a rotating celing (rotating ring).  Pipe is fed trought the top, our machinery will rotate several times around and weld the pipe ends toogether, we remove our equipment, pipe slides down, repeat the process.  The major problem I encountered is how to ground the pipe.  The ground has to come out of equipemt (for telemetry purposes), attach to the pipe somehow, and be able to rotate around the pipe since the whole point of this structure is to not wrap cables around the pipe (for time saving purposes).  The only solution so far is some sort of slip ring, but this comes with some problems (current fluctutations, maintenance, wear, etc).  Any other ideas out there?Thanks.
Reply:Is the outside surface of the pipe clean and free of scale and such, where you can make good electrical contact with it?I'm picturing either block type contact of bronze that is spring loaded against the pipe and rotates around with the weld head, or a braided copper strap that wraps the pipe and is spring tensioned against the pipe as it rotates around with the weld head.If the strap ground idea fits into the details of this machine, I would favor this system over the bronze block type contact.  I have used the strap type system enxensively in high production pulsed mig of auto components for many years with excellent success.  The strap makes good electrical contact because it is plyable and conforming to the surface, and somewhat soft.  It is suprisingly durable as well, and continues to function well as it wears.  Additionally it is inexpensive, readily available, and simple to install.  A quick disconnect could be attached to one end for rapid setup.Let us know what you come up with.
Reply:The outside of the pipe will be "relatively" clean... no scally rust flaking off, but not buffed cleaned either.   Also, metal is exposed only 12" from each end.I had thought about using a tension chain attached to a trolley that would rotate the ground lead as to not get tangled... but did not know if that type of system existed... sounds alot like your strap system.  Let me look into that.  Thanks.
Reply:I'd +1 on the copper braid if you can, also for less money but maybe more fab work you could look into big brushes like the ones pictured below.Maybe have something fabricated to attach to the welding torch system, But electrically isolated and run under or next to the torch mount. I should add that when the ground is very close to the arc it can affect the arc direction.Anyway, the larger brush pictured is rated 200A , the smaller 150A in open air.Matt Attached Images
Reply:A couple concerns I noticed after looking at your picture.1 - I like the copper braid idea too, but do you have enough clearance between the pipe bug and the insulating coating on the pipe?  To use the braid ground strap idea, you may have to increase the area stripped of coating at the ends of the pipe sections.2 - If this is a pipeline construction machine, say on a lay barge for example, then how sensitive are you to the possibility of arc strikes?  My intuition says that the chance of getting one is pretty low with the large contact area of the copper braided strap.  But do you have a zero tolerance for arc strikes on the surface of the pipe?  If so, you might have to look at a ground connection that rides in the weld joint bevel and over the cap to ensure any arc strikes are in the weld area.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:@ MattI was looking into big brushes yesterday.  Looking at how to attach them to the bug... I would need at least two beacuse I was planning on grounding them to a seperate band in order not to arc to the pipe, but since the band has to open like a clam shell, there will be a spot where the brush will have to jump.... so we need at least two for continuity.@ A_DABWell, your words were profetic.  I was updated on the pipe lining and now we only have 6 inches of exposed pipe.  And yes, we cant have arc contact on the surface of the pipe.  So thats why I think a secondary band will be necessary.I will post another picture of the new concept as soon as I have it ready... I would apreciate any feedback.
Reply:This problem is very interesting….I will toss in my 2 cents…I will try my best to describe my idea.  Imagine a cable reel with an inside diameter large enough to accommodate the work piece passing through it.  (Cable reel is horizontal with the pipe passing through center axis).  On the top side of the reel, we fabricate a quick release manual clamping mechanism (band clamp).   Basically the operator would latch this device onto the pipe and allow the ground cable to wind itself onto the reel while welding.   When the weld is complete, the operator would release the latch to allow the ground cable to be pulled off the reel.  The ground cable would require some rigging to guide and then draw the cable off the reel between welds ( pulley and weight, or long spring).