Hello
Is there any difference in strength between equivalent box sections of ERW or RHS

Cheers
David

Electric Resistance Welded Rectangular hollow section.

its all one thing

Thanks
I have ERW and RHS here now and they certainly look different

I shall take a piccie and show you what I mean, maybe I'm getting the terminology mixed up

Cheers
David

Both exactly the same, generally the terminology difference in in the wall thickness, below 2.5mm is ERW and above is RHS

ERW is electric resistance welded and is generally thin wall section in the region of 1.6mm.

RHS is rolled hollow section not rectangular and as its name suggests is made in a different way. This has a much thicker wall thickness than ERW.

John

not true, both are exactly the same, they are all formed from slitted steel strip, roller closed and resistance welded, on a slit and weld mill.

(I have worked for a few years in the steel industry, though at a seamless tube plant, and my mate installs weld inspection lines at welded tube plants)

The differences such as more and less rounded corners, and exact weld position etc, vary from one tube mill to another, and you may see bright finished welded tube (usually the thinner stuff) and grey dull finished tube.

This difference is purely that a lot of the thinner stuff is slit and welded from bright finished cold rolled mild steel sheet whereas the dull ("black" finished stuff is slit and welded from hot finished mild steel sheet.

When buying mild steel sheet I always specify CRMS up to 3mm thickness as it is much cleaner to work with and needs less cleaning prior to welding.

I've always maintained that Ron's use of the term RHS in the book has been very confusing...I guess technically speaking unless tube is cold or hot drawn (rare for square/rect) then it is more or less all electric resistance welded rolled hollow section...regardless of size...

However, agreeing with Mark..the sizes we use are generally referred to as ERW square/rect tube.....if you ask for that when buying you will have the least problems.....the RHS terminology is more used for the bigger/heavier sizes.

Edit: Just noticed NSdev's response which very much corresponds with mine......so it must be true..

[Edited on 26/9/06 by Alan B]

But if RHS only describes tubing that is rectangular and hollow, it shouldn't matter how it's made...

What is DOM (drawn-over-mandrel) tubing called over there across the pond? In the US it's either called DOM or "seamless".

quote:

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Originally posted by kb58
But if RHS only describes tubing that is rectangular and hollow, it shouldn't matter how it's made...

What is DOM (drawn-over-mandrel) tubing called over there across the pond? In the US it's either called DOM or "seamless".

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Also dead right Alan B, CDS or CFS are cold finished seamless, usually drawn or pilgered down from hot rolled seamless tubing.

Hot rolled seamless or hollow bar are exactly what they say.

DOM is ERW tube drawn over mandrel and through die.

The state of the steel is more interesting/important than how the tube was made. I suspect that there are more then one locost rolling around with suspension gear made of hardened steel, annealed or normalized are much nicer.

I thought I would tag on a question here....

I was calling around for prices on tubing. I was asked if I wanted cold or hot formed tubing. Which one should I be looking for?

cold formed, resistance welded.

Hot-rolled has a burnt crust on the surface that must be ground (not sanded) before welding. It can be used but it sucks having to grind everything first.