Tube vs. Pipe

[stone]

i have dom and hrew on my buggy. the hrew parts that have been in flops have big dents in them and the dom sections have nothing. thats all the real world experince i can offer to this topic

 

[pheery]

who all do you know that pipe has failed? why has it failed? what happened? anybody have an experience? or is this all pbb talk?

 

[Rich]

Then why not spend the extra couple dollars per foot and go with 4130 instead of *comparitively* weak DOM ?

Because some of us don't TIG, and stress relieving every weld is a pain in the ass.

 

[SHINTON]

Would pipe be ok for using in my antiwrap bar?

(Basic design would be the tractor link up front, welded into a pipe or tube, with tube/bushings in the back on top/bottom)

I have that 1.75" tubing I did with group buy from Rich...any reason NOT to use it since I have 20' lying around?

Sam

 

[Rich]

I have that 1.75" tubing I did with group buy from Rich...any reason NOT to use it since I have 20' lying around?

Sam

Should be strong enough, it's only 10% weaker than 1.5" .250.. I say go for it.

 

[rockcity]

Then why not spend the extra couple dollars per foot and go with 4130 instead of *comparitively* weak DOM ?

Because 4130 is brittle and a PITA to weld and stress releive, as Rich said. Don't get me wrong, I'm using some 4130 parts on my buggy, just not the cage.

And, DOM is $$$ enough. TIG welding isn't the hard part, its all the work involved prior and after welding thats a PITA.

And, most comp buggies don't even use 4130, so why would I as a recreational user?


I've got some 1.5" x .25" DOM if you need some. I can ship up to 6' lengths

Rob

 

[pheery]

who all do you know that pipe has failed? why has it failed? what happened? anybody have an experience? or is this all pbb talk?

anybody? bueller, bueller, anybody?

 

[Rich]

Pat - it all depends on what size/thickness of the pipe.. You CAN make it as stong as tube, it just needs to be thicker, and therefore heavier.

Just saying "a pipe cage failed" means very little. a DOM cage would easily fail too, if you use 1.25 .063 tubing

Yours has obviously been used, and is holding up...so run it, and don't worry 'bout it.. Again, the design is more important than the material anyway...

 

[pheery]

it isnt a challange, i am actually trying to educate myself here with real world stuff not hearsay. curiosity is getting the best of me, apparantly people have some vast knowledge through racing applications and what not, i really would like to know more about the actuals, not just what everyone reads and hears.

but my experience has been that pipe works, as has several others. but i agree that design is key.

 

[Rich]

I hear ya, and please don't misunderstand me, I'm with ya on this.. Just that alot of what we might hear about failed cages could have just as much if not more to do with the design rather than the materials involved, or the trails run, or, or,...

The variables kill it IMO, so "real world" is really hard to use...

Along the same lines, you'll always see something like this about "what tire to run".. Some guys will swear by the more extreme type tires like Krawlers, IROK's, SX's, etc.. and then you'll get a "well, my BFG All-terrains have never gotten me stuck before"

If you remove all variables such as design, material size & thickness, etc... you know that structural pipe is lowest in strength (other than poop pipe), followed by the 1010 rolled tubing, then 1020 DOM, then the 4xxx cromo, on and on... It all just depends on how comfortable you feel with each, right?

For example, my cage is 1.75" OD .120 1020 DOM.. If yours, with similar design, struct. pipe at ~1.5" ID sch.80, might be every bit as strong (assuming your batch is consistant in thickness down the length of the tube), it'll just be alot heavier.

IMO, the consistency matters alot too, since you either make all your designs assuming the worst (thinnest), or you're misleading yourself (I think Braxton mentioned this?)

Some good data in this thread, despite some of the pissing...

 

[drkelly]

Would pipe be ok for using in my antiwrap bar?

(Basic design would be the tractor link up front, welded into a pipe or tube, with tube/bushings in the back on top/bottom)

I have that 1.75" tubing I did with group buy from Rich...any reason NOT to use it since I have 20' lying around?

Sam

Sam,

I built my traction bar out of pipe. It was fairly thick, but I don't remember schedule number etc. I ran it on my Bronco for 1 year, which was a lot of wheeling that year, and never had a problem.

Here is a picture:

I made the crossbar from a piece of pipe also and some cut up brackets I got out of the dumpster at work:

Danny

 

[SpydyrWyr]

Looks good! That's a testimonial for tension/compression loading for the pipe. However, with regard to exo/interior cages, the loading will be more impact, bending moment, and shear.

 

[drkelly]

Good comments from Rich about weight as well. Pipe is NOT heavier than tubing when talking about material density. I am tired of people stating that. It is only heavier if you use thicker wall material in an attempt to achieve the same strength as DOM. The way that statement gets thrown around I think some people out there actually think a piece of pipe the same length and wall thickness as DOM is heavier.

After all this, I will probably have a horrendous roll my first trip out and crush my cab. I am treading on thin ice with my cage though because I am using schedule 10 pipe that measures about 1.9" OD and has a wall thickness of 0.105" in an effort to keep the weight down. I would not have done this on a Jeep or open top vehicle, but this is an exo-cage. If it rolls on jagged rocks, it will most likely dent easily as Stone mentioned his HREW has.

DK

 

[shawn]

Because some of us don't TIG, and stress relieving every weld is a pain in the ass.

Hmmm.... seems like I heard that before.... who was it.... all the way back on PAGE ONE of this thread.... um.....

 

[braxton357]

Point is, saying things like "noone's life is worth the extra couple dollars saved" when debating pipe-vs-tube is pretty irrellivant. If that is your sole argument, then you're only doing yourself a disservice by "just" using DOM.


P.s. Plenty of rockcrawling chassis builders are using crmo for comp rigs. None that I know of stress relieve further than hitting it, and a couple don't even tig it.

 

[Rich]

as I understand it, you're only going to reap the benefits of the cromo if it's Tig'd with the right filler, and then stress relieved, otherwise, it's only as strong as the weld, which is no stronger than 1020?

 

[shawn]

Not necessarily. I mean, it's best if you do. But you can GMAW or GTAW it up to .120 wall thickness without having to worry too much about stress relief. That's assuming you know WTF you're doing with a welder in the first place.

 

[braxton357]

as I understand it, you're only going to reap the benefits of the cromo if it's Tig'd with the right filler, and then stress relieved, otherwise, it's only as strong as the weld, which is no stronger than 1020?

They're doing it for dent resistance. But yea you're pretty much right.

 

[rockcity]

OK, well, I've had a thin wall (.095") chromo weld crack and IMO fail due to not stress releiving it. I've welded lots o 4130 and you "can" weld it all sorts of ways, but its not necessairily the process of welding, but rather the stress releiving it that is important. I've even stick welded it, but for a cage, I'd TIG and stress relieve it, if not, it will break at the weld. The weld will not fail, its that small part just past the weld where it fails...

I'm no engineer so I have to rely on experience and common sense. Pipe is for pressure applications and tubing is for structural applications, its made that way for a reasone. Sure design is key factor, but why design with the wrong material for the application? I only know from experience and not "hearsay"

I'm not saying Pipe cages are bad, I'm just saying I wouldn't build one and don't expect me to ride up Lion's Back @ Moab in one...

and yes, there are a lot of chromo comp rigs, but compare that to the total amount of comp rigs out there and then do your figuring...

Rob

 

[rockcity]

They're doing it for dent resistance. But yea you're pretty much right.

they are also doing it for the weight, but minimum is 2500# and a lot of the moon buggies are close to that anyway without chromo

 

[shawn]

OK, well, I've had a thin wall (.095") chromo weld crack and IMO fail due to not stress releiving it.

It couldn't hurt. But that's per .... um.... either Miller's or Lincoln's.... not sure which.... ASTM? Damn, now I'm going to have to find it.

But yeah, some-damn-body semi-official said you could do 4130 with any process up to .120 wall thickness, no stress relief. They were referring specifically to car and airplane applications, and I was looking at it not more than a month ago.

I'll see if I can find it and let you know the specifics. I agree, tho..... if it were me, spending the extra cash for the chromoly, I'd be spending the extra time on the stress relief regardless.

 

[braxton357]

they are also doing it for the weight, but minimum is 2500# and a lot of the moon buggies are close to that anyway without chromo

Not so much in rockcrawling as they do in nhra or scca type racing. The only weight advantage crmo has over other tube is that in most sanctioning bodies you're able to use thinner tube... People are still using 1.5x.120 in most places, they're just using crmo...because as you said, there really isn't a need to go much lighter anymore, just stronger...and more expensive.

 

[rockcity]

oh yeah, def. but if they are using 4130, I can damn well bet they are welding it properly and such. I just don't have the time, money, or patience (unless I'm getting paid) to do it...

so I'll stick with the 1020 DOM

 

[CasterTroy]

your a mechanical engineer? shouldn't you have learned things of this nature? or am i completely off in what engineers do?

There are several different fields of Mechanical engineering

MFG engineer
Fabrication engineering
HVAC engineering
Plumbing Engineering
Electrical engineering


All can derive from a degree in "mechanical engineering"


BTW...hellova topic (asside from the pissing and moaning)

 

[thurgood]

"4130 is an air hardening steel. ..... At the completion of welding, the entire area surrounding the welds should be eavenly heated to about 1200 degrees F and allowed to cool in still air or covered in lime or dry sand."

From Caroll Smiths "Engineer to Win"

"Right up front, I will tell you that it is not possible to accurately stress relieve a welded 4130 steel assembly by heating it red-hot with an oxy-acetlyene torch in an open air workshop. Stress relieving a welded 4130 assembly such as an aircraft engine mount or a race car rear suspension member is a metallurgical process that requires at least six hours to do correctly. The steel grain structure must be brought up to about 1150 degrees F, held at that temperature for several minutes to a couple of hours, then slowly cooled back down to room temperature. This very specific process absolutely cannot be accomplished by a hand-held torch in a welding shop."

From Performance Welding by Richard Finch


So yeah, the most reliable source for info on building race cars says to stress relieve it, but another book on welding says its not possible to do correctly, so don't try because you'll weaken the metal more than just leaving it in its natural state. I don't stress relieve 4130 after welding and I've never had a problem, but I work on tiny stuff and don't magnaflux it to make sure.

Typically failures occur beyond the weld at the edge of the heat affected zone from what the books say.