THSCC Forums

In the case of an older, pre-existing rollcage, how does one determine if the tubing is either ERW or DOM? The new SCCA rules require DOM, but how can they or anyone tell?

_________________
Rich
http://www.v8mongrel.com/

ERW (Electric Resistance Welded) Tubing is recognised by the weld seam running along the outside, parallel to the axis of the tubing. However, the weld seam is more easily seen by inspecting the INSIDE of the tubing, since most ERW tubing is polished along the weld seam on the outside diameter, making the seam less noticable. Always look for the weld seam INSIDE the tubing.

DOM (Drawn on Mandrel) Tubing is seamless. It has no welds. It is manufactured at the steel mill using a hot-drawing process to assure a fully annealed (stress-free) condition.

How's that??

_________________
Brad

Thanks, that works. Now, on cage that is in a car, how can you tell if the seam, like you said, is poished on the outside?

_________________
Rich
http://www.v8mongrel.com/

I'll assume the cage is painted, so you should remove the paint around the circumference forming a ring, say, 2" in width, in an easily-accessable area. Use a paint solvent or a wire brush (or both). DON'T grind or sand it off. That would defeat the purpose. Try to leave the surface just as it came from the mill.

Upon close inspection of the, ahem, aforementioned cleaned area, you should then be able to make out either the weld discoloration or a shaded "line" maybe 1/8" wide, since the "polishing" that is done on ERW isn't really for cosmetics. Rather, it is done to reduce the weld bead down to the specified O.D. for the tubing---removing the "bump", as it were.

Really bad ERW Tubing is liable to have a line of pitting running along the weld area, where the bead failed to fill the entire seam. That would be really easy to spot.

Even if it's high-quality stuff the weld should be fairly easy to discern with a work-light.

Hope this helps.

_________________
Brad