Differnece in Tubing

[Tau44]

I am confused?

What is the difference in DOM and HREW tubing? Pro's and Con's? Which one is better if you are going to build roll cages or something like that. I have seen roll cages advertised as being built in both of those. Which is better and safer?

Is OD tubing and HREW tubing the same?

Help, I am confused.......

Thanks,

Tau

[walker]

DOM is "drawn over mandrel" and hrew is "hot rolled electrically welded". DOM is the high dollar truely seamless tubing. Electrically welded is the common stuff. There is also a spiral seamed tubing, that is welded, that is called seamless too. Clear as mud? Good.
Now as far as roll cages go I think common tubing is fine, but do whatever your sactioning body saya if you are racing.

[snow]

There really is quite a difference between the two.......The Dom will be made of 1020 steel and of uniform thickness through out.......The ERW will be made of 1010 and not of uniform thickness.......... A strength difference of around 20,000 psi.........

The Dom is superior in all aspects........including the price....it costs twice as much.........

As has already been mentioned, You need to check the rules, the materials may well be specified.......

Most roll cage kits will be made of the ERW........with thousands of them out there, I cannot say that they are unsafe........BUT, A cage made of DOM will be SAFER....... In my book, DOM is worth the extra cost.........There are places to save money.......This is not one of them.....

[Compchassis]

This is where sanctioning bodies drive me nuts. Many of them specify that the fastest of the cars can be built only of moly tubing, and they only distinguish by moly and mild. They do not adress the fact that there are several levels of mild steel tubing. Not only that, but they allow moly cars to be built out of much thinner tubing, yet a car built out of thicker wall DOM tubing will in all likely hood actually be stronger than the moly car.

[Tau44]

OD is the thickness of the wall of the tubing? Is that correct?

THanks,
Tau

[Compchassis]

OD is the outside diameter of the tubing, ID is the inside diameter. Wall thickness is just that, the thickness of the wall of the tubing. The difference between the OD and the ID, divided by 2 is the wall thickness.

[tomasharvey]

This is from the NHRA.

A roll bar is required in any convertible running 13.99 seconds or quicker in the quarter mile, and in other cars beginning at 11.99. The roll bar is accepted in vehicles running as quick as 10.00 second e.t., provided the stock firewall and floorboard is intact, other than for installation of wheel tubs. The rollbar must be constructed of minimum 1 ¾ inch o.d. x .118 inch wall mild steel tubing, or 1 ¾ x .083 chrome moly tubing, and must conform to the following diagram:

Go to http://www.nhra.com/contacts/tech_faq.html for a good description.

One note of caution, I would suggest you buy your tubing from a shop that understands NHRA or what ever sanction body your dealing with. Many NHRA suppliers will guarantee the wall thickness. If you plan on running a certified cage the tech inspector with use a UT thickness gauge to ensure the wall is thick enough. Also, they will VT or visually check your welds. You cannot grind welds and it is best not to paint the welded area until it passes. Hope your building a drag car!

Tom
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