input needed: Why tubing and not pipe for rollbar/cage?

I've purchased and installed 2-12 point cages from Chris Alston. They meet NHRA specs. and can be used with confidence. Art Morrison would be just as good, and there are probably others. They will bend the main hoops to your needs. The price is not high. A 4 point roll bar is $162 and a 12 point cage is $278, in mild steel tubing. You can't match the uniformity of the bends with a home bender. A roll bar is required if running 11:00 to 11:99. A roll cage is required for 10:99 or quicker. This is for door cars. Get a NHRA rule book and study it thoroughly or you probably will get booted out during tech. at your local sanctioned drag strip.

 

Actually, NHRA lowered the requirement for a roll bar down from 11.99 down to 11.49 this year. So, for a full body/OEM floor'd hardtop car a roll bar is good from 10.0 to 11.49. Faster than 10.0, and a roll cage is needed.

The roll bar requirement for a vert is 13.49.

If you're still thinking of having your friend bend the tube on a "bow and arrow" bender, do some test bends first. Those bender tend to crimp the tube inside the bend, not saying his will, but just in case, do some test bends first. I like rotary draw benders for roll cage work.

Get a rulebook, don't cheap out on safety equipment, and have fun!

Hank

 

Not all pipe has welded seams. I specify seamless pipe all the time. I won't use it for a roll cage, though.

 

I was in the dark about pipe/tube/and dom myself untill I studied it.
I had to check the net for refeshing my memory but here it is in quotes
"
[FONT=Arial,Helvetica,sans-serif]Pipe vs Tube[/FONT]


[FONT=Arial,Helvetica,sans-serif] What's the difference between a pipe and a tube?[/FONT]

[FONT=Arial,Helvetica,sans-serif] More often than not, people guess it has something to do with the quality of the materials, but that's got nothing to do with it. The difference between a pipe and a tube is how they are measured, and ultimately what they are used for. [/FONT]

[FONT=Arial,Helvetica,sans-serif] A pipe is a vessel - a tube is structural.[/FONT]

[FONT=Arial,Helvetica,sans-serif] A pipe is measured ID - a tube is measured OD.[/FONT]

[FONT=Arial,Helvetica,sans-serif] How they are measured... Pipes are measured ID or inside diameter because they are vessels. Tubes are measured OD or outside diameter because they are structural. [/FONT]

[FONT=Arial,Helvetica,sans-serif] Pipes have a consistent ID regardless of wall thickness. In other words, a 1/2" high pressure pipe may need a 2" thick wall, but the ID will still only be 1/2" even tho the OD is 4.5". [/FONT]

[FONT=Arial,Helvetica,sans-serif] Generally speaking, a tube will have a consistent OD and it's ID will change. Engineers see tubes and pipes with different eyes. [/FONT]
[FONT=Arial,Helvetica,sans-serif] A tube is structural.[/FONT]
[FONT=Arial,Helvetica,sans-serif] By having a consistent OD they can vary wall thickness, changing the ID, to increase strength. Because they are consistent OD, they have predictable characteristics. [/FONT]

[FONT=Arial,Helvetica,sans-serif] Again, the difference is simple, it's how they are measured and what their intended uses are."
There you have it. the only technical difference between pipe and tube is in how they are sized for engineering purposes, not the materials or workmanship.
from an engineering perspective the inside diameter of pipe is fluid flow essential. Volume is transmitted through a space.
The external diameter of tubing is essential because stress is transmitted along a surface.
Both electrical and mechanical stresses are transmited at the surface which is why a 2" tube will support in compression and tension almost as much as a 2" rod. This is how a small scratch in the surface of a car part can cause it to fail. it's how you can rip a bar of steel apart with your hands by bending it if you score it with a blade first.

I would assume the "pipe" thought of as inferior in quality was water pipe made of mild steel and not carbon, tool, or chromium-molybdenum steel.
Most all pipe is formed from sheet, rolled, welded and with the case of dom is drawn over a mandrel and worked further to guarantee consistency. just like hammerwelding a joint.
that mandrel has to be attached at one end or the other to something it can't float in the middle of the pipe magically resisting movement and if it was at the finished end...where does the tube go?
The mandrel is fixed to the beginning end of the tube/pipe forming process. sheet is wrapped around the mandrel, welded and then stepped through dies around the mandrel to size it. it is drawn meaning there is a pulling of the tube from the finished end, it is not being pushed over the mandrel. I don't remember much about the non welded pipe but seem to remember they essentially forge the billet into a thick short blank with a hole in the middle then roll it smaller and thinner as it gets longer.
[/FONT]

 

That's not accurate. For a given stated pipe size, the OD remains the same regardless of Schedule number (wall thickness). As the wall thickness increases, the ID reduces. http://www.engineersedge.com/pipe_schedules.htm

Bob

 

Found this but yup I guess pipe isn't exactly the same inner diameter as the nominal identification calls for:
Pipe vs Tube

Round pipe is commonly available even at your local hardware store. Tubing is available at your metal supplier. Price the material beforehand, and steer clear of seamless tube (aka DOM, drawn over mandrel). It is very expensive.
Tube is called out by the outside diameter (OD). A 1" round tubing will be exactly 1". Tube is available in thin wall (0.065") and thick wall (0.125"). To find the inside diameter (ID), double the wall thickness (ie .125x2=.250") and subtract from the OD.
Pipe is called out by its inside diameter rather than its outside diameter. Therefore a 3/4" pipe will actually measure 1.05" OD. A 1" pipe will measure 1.315" OD.
Though the pipe is called by the inside diameter, the actual ID is slightly greater. A 3/4" schedule 40 pipe has a wall thickness of .113". The ID is therefore .113"x2=.226". 1.05"-.226"= 0.824".
Why Doesn't Pipe's Real ID and Called ID Match?

Advances in pipe making are to blame for the mismatch between the called out size and the actual size. Old pipe was weaker than today's pipe, and to perform at the rated pressure had to have a thicker wall than is necessary for modern pipe.
But if the OD size of pipe was shrunk, new pipe would be too small to fit old pipe fittings. So the wall thickness became thinner and the ID increased.

 

I have used pipe, I think if its just for a street rod that may or may not get crunched ..I will use it..but you never know , the dragstrip another thing, follow the rules,

 

Perspective here guys. The guy is building a street car and is using the steel to replace the wood that holds the body together, add a bit of a safety factor, and may show up at the drag strip sometimes.

Doesn't sound like a mid 11 second car to me. Slower then mid 11 second most drag associations do not require a roll bar at all, so he will be above the curve with any form of a roll bar. Been to the HAMB Drags, a true street driven rod that can run mid 11s is a rare critter. I suspect they would not turn away a car with a cage built from black pipe if the welds were good and the car was slower then the speed requirement for a roll bar.

Since it will be a street car, there is a good chance the roll bar material will be covered by an interior, or almost hidden by tin work. I can invision holes drilled into the roll bar to mount stuff. Black pipe was used for years and years in roll cages on circle tracks across the country and many were mashed bad, bent baddly, but still held up. I guess for the intended purpose, the black pipe would do the job, and would offer much more protection then the original rotted out wood structure.

All that said, it would be advisable to see what the cost difference between the pipe and the tubing and make a decision based on the information available. The amount of roll bar material required to build the car may have an effect of which direction to go, as could the availability of the dementions of material needed. The tubing offers several advantages over the pipe, but how the car is finished could effectively remove or reduce a lot of those advantages.

Now, IF he was building a car intended for racing, tubing would be the smart way to go. Gene

 

the biggest difference between the two in simple terms is pipe is made to carry stuff inside. Tubing is structural. Pipe is not made to be structural. Tubing is the way to go period.

 

pipe is made to be straight, you can bend it , but it wasn't designed to be used that way. I'd do the tubing cage. After all its "just" your family.

 

http://www.steeltubeinstitute.org/pipe_applications.htm

Would you be surprised to know you've driven over bridges, and sat at ball games built with pipe for structural support?

Would you be surprised to know that you can get pipe in many different grades of steel?

The problem is blanket statements. And this is a never ending Internet Special Olympics event.

Being this is only a 3 yr old thread, I've got no post, and don't know shit I'll turn the soapbox over to someone better qualified to edumicate the masses.

 

I'm gonna edit ya

"the biggest difference between the two in simple terms is pipe is classified to carry stuff inside. Tubing is classified for structural use.
Both are made by the same manufacturing process' out of a variety of same materials to meet the need of different purposes."
...which is better than I could have said without ya

Or in my own findy words, I think the only difference between pipe and tubing of equal size, formed from the same gauge of the same steel is one of nomenclature and application not a difference of physical properties.
Y'all are taking the difference between hard, cold rolled chrome-moly steel compared to softer, cold or hot rolled low tensile strength steel and applying that knowledge to 2 words "pipe" and "tubing" neither of which literally has anything to do with describing structural physical properties and everything to do with a name reflecting what yor going to use it on.
I'm surprised someone hasn't said yet "How come brake tubing isn't called brake pipe" or how come we say the phone rings when it has a speaker not a ringer
It's like asking...what covers the engine better, a hood or a bonnet?

 

pipe could snap and not just buckle or bend like tube.

 

Why?

 

Because it is weak..As you said its not made to be structural. If a car flips it might not hold its weight.

 

No it's not, you are in a word, WRONG. They are different. Nice of you to play but to give that advice is pretty bad. Try welding black pipe, which is what he is talking about using, and regular steel tubing. Big differences that you can tell almost instantly. You can also tell if you put it in a bender...

 

I think your all wrong...and right at the same time!

I've used pipe for lots of stuff...never had a problem bending or welding it.
The wall is thicker so any difference in material strength SEEMS to be made up by that difference in thickness. I don't know that for sure though. I'm not an Engineer....
There is a weight penalty due to the thicker wall of course.

I think theres just such a variety of materials that "pipe" can be made of, that people tend to grasp onto the worst and apply it to ALL pipe!

Pipe snapping off...seems to me that people are thinking of the old super brittle CAST iron pipe of old. Nobody is gonna use that...but its "pipe" so it gives ALL pipe a bad name.

You can bend the crap out of real steel structural pipe.
I've bent it with my home built HF style bender into all sorts of bumpers and rock sliders etc for 4x4's...no issues unless you try to bend it with the weld seam on the outside radius of the bend. Then the extra resistance from the weld will have the pipe refuse to stretch properly and usually split across the weld seam.
I always use the seam as a side guide to keep the bends level so the stretching across the seam is a non-issue. Never had problems.

On Pirate4x4.com there was a huge thread about pipe VS tube for rollcages.
A pipe "supporter" made a complete Exo-cage for his Toyota pickup and then rolled it over consistently thru a season of 4 wheeling.
End result some bumps, scrapes...minor misalignment and a crack in a weld on a lower corner...more from normal flex/vibration than any issue with strength.
Tube would have formed the same crack due to the design lacking any gussets in that area and vibrating in normal use.

Pirate members basicly had to admit that pipe wasn't nearly as bad as everyone made it out to be! That was a REAL WORLD test and the multiple rock impacts to the pipe cage simply don't lie!

Tube is the best to use in a build where you have access to the proper bender and the extra cash...but if the fabricator is willing to do a quality install despite using the cheaper pipe, it CAN give good results.

The key is to do a good install with good joint fit, careful welding and proper gusseting. Pretend your using the finest DOM and it will work. How could it not? It's still thick, malleable steel...not bamboo!
The problem is that many people will just throw a cage or whatever together with less planning and care IF its pipe, than they would if it were precious DOM tube.
If your sloppy your results are compromised right from the start...and it doesn't matter what material was used.

 

Back in the late 60's /early 70's my dad built lots of circle track roll cages using schedule 40 gas pipe. I personally some of his cages and similar other cages take some nasty rolls and flips without breaking or anyone getting injured. I have built alot of projects using gas pipe, an it bends and welds nicely. I would not use gas pipe in a race car now because tubing is so much nicer and it fits my bender the way it should. Stick welding is not allowed by most sanctioning bodies and I really don't know why because it is as strong as any other welding process, but rules are rules.

 

I hear people talk about pipe spliting and breaking on impact, quite frankly, I've not seen this happen any more then I've seen tubing split under the same conditions. I have seen a main hoop roll cage tubing shear off at a frame, but I suspect it was improperly welded chrome moly.
I spend many years around dirt track racing, back in the days when pipe was what you used for roll cages. I've see pipe smashed close and twisted like a pretzle without splitting or shearing off. Seen cages wrecked so bad, there wasn't a straight pipe in the whole cage, the material held up just fine.

Many of the cages that failed back in the day, were built from conduit, poorly welded, or poorly designed. Many car fabricators figured the easiest way to make cars faster was to reduce the weight of the cage, some truely scary stuff started showing up and failing at an alarming rate. Many sanctioning bodies began requiring a minumium wall thickness. To get that mimumium wall thickness required the use of tubing, because pipe was too thick, and conduit was too thin. Once the tubing was the normal, pipe cages started disapearing, because of the weight, not a safety issue. Somewhere along the line, the pipe got the bad rap for all the crap that was used before the mimium thickness wall was adapted. Before the use of tubing happened, cages failed, so the pipe must have been the problem - not.

Nothing wrong with using tubing for a roll cage, and if weight is not a factor, nothing wrong with a pipe cage either. Just cut off the threads, and remove the paint before welding. Gene

 

I've seen plenty of stock cars and owned a couple with the heavy black pipe roll cages. Maybe not the prettiest things in the world, but I never saw one fail even in heavy crashes.

Advantages: It is easily available at Lowes, Home Depot, etc. Cuts and welds easily. If you screw up a piece, toss it and make a new one since the price is right.

Disadvantages: Heavy, not as nice appearing as tube, "experts" who got no clue will get in your face about it.

I still see it used on saturday night special stock cars for rub rails and bumper reinforcement.

Bob

 

One night at Islip Speedway, my brother walled someone that really was begging for it and the car folded up like a tromped on beer can. After the car was brought into the pits we had a look and the entire front cage was built from either .050 or .065 wall tubing. I can see building in a "crush zone" but this was dangerous.

Bob

 

So where are you guys shopping that DOM tubing is prohibitively expensive?

 

I am a newbie, but this is what I do for a living.D.O.M. is more expensive and not needed. Get erw tubing 1 3/4 .130 wall and it will do great for your application. If you are going to have a Cage not a roll Bar then you can get by with 1 5/8 .130 wall.. I have had a customer wreck at 160 with a 3000 lb. car flip 6-8 times on a concrete wall with a erw cage and walk away un hurt..I tig weld everything for strengh and looks..I buy mine from Shapiro supply you can google them,you get a good price break when you buy 4 or more sticks. I have been 3.90's in the 1/8 and when I started racing(second generation) my dad told me " if you got a $10 head put a $10 helmet on it"..So I am one to do something right and SAFE..ANYTHING CAN HAPPEN ON THE TRACK!!!!!!! Good luck, Dan Parker parkerchassis.com

 

Not needed? Depends on how you look at it. I work with both ERW and DOM tubing every day, and I can say with confidence that the DOM holds its shape better when bent, TIG welds more smoothly, and is MUCH better for machining, when necessary...so maybe there is a difference in material properties. Plus, the wall thickness tolerence for DOM is much tighter, so you can use .120 wall tubing (instead of .134) for straight chassis members without worrying about sonic testing, resulting in a lighter chassis structure.

When bending ERW, the tube seam should be aligned on the inside of the bend to relieve tension stress on the seam. This is also not necessary with DOM, as the seam area has been stress-relieved in the drawing process.

To anyone who thinks hardware store pipe and tubing are the same material...try this. Take a piece of 3/4" SCH40 black pipe and a piece of 1"X.134 wall ERW tubing. Smash the first couple of inches flat with a hammer. The pipe will usually crack along the sides, the tubing almost never does. Does it matter in a roll cage application? Probably not...but maybe.

 

I agree dom is a better choice,if you get a roll bar kit from anybody,chassis eng.,S&W, etc. they are all erw in the 6 point mild steel. I have never seen erw fail in some BAD wrecks.I have seen chromemoly fail many times(mainly because of improper welding,another subject). But for the average guy I believe the erw will do just fine and 10 times better than the pipe he original question was about. You are correct on the .134 wall thickness I had a brain fart this morning..Just my opion. Thanks Dan

 

just don't use pipe, end of story. You really don't need to understand more than is already on this thread, just don't do it.
have fun
wil
www.sakowskimotors.com

 

and why is it weak?

 

My old business used A500 pipe structurally, mill certs showed minimum 50 KSI yield, 65 KSI tensile. Only reason not to use it is weight and bender won't have oddball size dies.

 

Looking at this thread again, I think I see a problem...or at least a source to some of the confusion.
I think everyone is in agreement about DOM being the very best to use IF its available in your area, IF you have a proper tube bender available AND if DOM is not priced thru the roof due to its being Special order only...as it seems to be around my province!

The BIGGEST confusion seems to be the definition of "pipe" itself!
The stuff I've been using is, I think(!), ERW Schedule 40 structural PIPE.
Is it correct to call this ERW steel "pipe"?
It's listed by schedule size and inside diameter around here...so I've been calling it pipe.
Now I'm seeing some guys here calling it tubing.
Is it available both ways????

I'm wondering is there a huge difference in everyones local pipe quality, (due to the EASY availability of DOM in that area), that makes one guy say pipe welds like crap while in some other area, myself and others have welded it effortlessly.
One guy will say its easy to snap...another will put his life on the line under a cageful of it.

Now...thats weird to me.

Guys who haven't used it at all spout off all kinds of old wives tales and drivel of course, but thats normal. It's the internet!!! Lol

BUT...there are some quality builders on both sides of this fence and that makes it very interesting to have so many wide variations on if "pipe" really is good or bad.

I'm wondering is this "structural pipe" something that the steel suppliers came up with to allow building contractors or whomever a way to have quality ERW strength, while still allowing the use of the easily portable PIPE style benders and even the ability to use pipe threaders on the ERW to allow screw together construction where needed in certain jobs? Like custom Scaffolding or lighting towers...or anything along those lines...

I'd really like to see a "supplier" come on here and explain just how much difference there actually is in weldability and strength between the common grades of Schedule 40 "pipe"...never mind trying to compare pipe to DOM!

 

It doesn't take a supplier. Just a little research. Why worry about whether those long lengths of tubular steel are called "pipe" or "tubing". What's important is that you use a materials of sufficient strength to avoid failure. Sanctioning race organizations normally specify "tube" because it's implicit that the grade will be ASTM A500 series, whereas allowing pipe would likely to lead to roll cages made from any unknown variety of materials. Here's the structural tube grades:

ASTM A513 Type 1
Hot Rolled Electric-Resistance Welded (ERW) Carbon Steel Mechanical Tubing
ASTM A513 Type 2
Cold Rolled Electric-Resistance Welded (ERW) Carbon Steel Mechanical Tubing
ASTM A513 Type 3
"Sink Drawn" Hot-rolled Steel
ASTM A513 Type 4
"Sink Drawn" Cold-rolled Steel
ASTM A513 Type 5
Drawn Over Mandrel (DOM)
ASTM A513 Type 6
Drawn Over Mandrel Special Smooth ID (SSID DOM)
ASTM A512
Cold-Drawn Buttweld Carbon Steel Mechanical Tubing
ASTM A519
Seamless Carbon and Alloy Steel Mechanical Tubing
ASTM A500
Welded Structural Tubing

This doesn't mean that "pipe" won't do the job. Some grades have a yield strength greater than the ASTM 500 materials. Pipe can range in yield strengths from as low as 30K to strengths exceeding ASTM A500 tube, but most guys using pipe are going to get A53 from the plumbing supply store instead of the less common higher grades.
What matters is that you know the material properties, and size the pipe or tube in the structure correctly. You could build your roll cage out of wood if you use enough of it, but it wouldn't have a favorable strength to mass ratio. Same applies to steel. Use pipe with a 30K yield, and it'll take more of it than using A500 tube.

Bob