Aluminum Pipe Bus splitting

[apowerengr]

Does anyone have experience with 3" AL pipe bus splitting along its major axis for 1-3'? This is not a welded joint, the installations are outdoor, open air bus supported at 20' spans, no other mechanical loads exist, connectors are bolted-mechanical connections with aluminum bolts which were torqued per specs, the pipe is not deformed or oblong, no significant through faults have been experienced, load is not more than 50% of the rating of the bus per Alcoa tables, there are not end plugs in the pipe so water ingress/freezing should have plenty of room to expand without splitting the pipe.......I don't know what to think.

The visible splits are on the bottom of the pipe with the gap at the split 1/4" wide.

The installation is approximately 20 years old.

So I'm thinking can the splits just be welded or does the bus have to be replaced?

Any thoughts are appreciated.

 

[ruggedscot]

Whats the atmo like where you are any thing that could be corrosive to aluminium ?

Welding would I think cause you problems, it amy alter the characteristics of the bus and give you hot spots... replacement is probably the better bet here,

 

[Marmite]

UK practice is to fit plastic end caps to Aluminium busbars to prevent the ingress of insects, birds, moisture and other pollution. The end cap has a 2mm hole for pressure release. Is it possible that moisture has pooled in the bottom of the tube and eventually corroded through? If so I would replace the tube and fit end caps, or you could possibly fit stepped connector plates at one end to make the tube self draining. If you replace the tube it will give you the chance to cut it in half and identify the root cause of the split. It's probably cheaper than trying to weld the old tube in any case.
Regards
Marmite

 

[Compositepro]

Sounds like freezing water caused the problem. The water probably collected in a sag in the tube. Water at the interface between filled/unfilled tube would freeze first because of the extra heat transfer along the unfilled tube. This will form plugs on both ends of the water filled tube section. When the rest of the water slowly freezes the tube will burst.

I've seen a steel tube in a farm-tractor frame split by freezing water.

 

[subtech]

Along with the water, you can expect animal inhabitants as well. Animals bring debris of all sorts.
As soon as possible, I would inspect the bus for a buildup of debris which can hold not only moisture, but corrosive contaminants.
Another point to consider is mechanical stresses caused by oscillation. Your bus should have some means of mechanical dampening employed. Where I work, we install 266 Kcmil ACSR inside 3 in. tubular bus (nearly its full length) to dampen oscillations. Larger tube bus usually requires a larger diameter conductor.(We use 397 Kcmil ACSR in 5 in. tube bus)
The ends of your bus should be capped. We use aluminum caps supplied by the tubing manufacturer. They are tack welded in place.
It is wise to employ "weep holes" in the bottom of the bus tube mid span between support points anywhere the support points are 12 feet or further apart. Three weep holes approximately 3 to 6 inches apart, 1/8 in. to 3/16 in. diameter are commonly used.
If you choose to weld the cracks in bus, I would highly recommend that you consult the tube manufacturer for advice on tube prep, welding method, and the alloy of fill rod or wire to be used.

 

[waross]

If the splits are parallel to the flow of the current and not affecting any hardware, why go to the expense of welding? How about a non metallic filler. Quick and cheap and it will prevent the ingress of insects and dirt.


Bill
--------------------
"Why not the best?"
Jimmy Carter