DOM vs ERW tubing ID?

||The answer is really simple, I think. || ||NHRA uses an ultrasonic inspection device. ||It is able to resolve variation in thickness down to a few ||thousandths. of an inch. I believe that it will work through ||paint, though with some loss of accuracy. It should be able ||to pick up the seam of the tubing. ||The regional technical folks may be able to help you or ||suggest who may have the equipment to do it for you. ||Here's the Southcentral chassis inspectors. ||

Great! We'll just specify that new logbooks will only be issued to cars with verifiable tubing documentation or an NHRA tech certificate :)

|| || ||Rex B wrote: ||> ||> I have a car with a rollcage installed when I got it. ||> Racing organization rules now require DOM-only construction. ||> Is there any way to tell what this cage is contructed from, without cutting it? ||> Texas Parts Guy

Texas Parts Guy

What can't you use paint remover on a portion of the hoop and look for the weld HAZ? Is this a "I have to check one car, once", or "I'm SCCA Regional Tech and I have to check 100 cars all on the same weekend"?

Since I'm in sort of the same business (CASC tech inspector), what certification is acceptable to SCCA? I have yet to be presented with any sort of certificate on the tube itself, but I have had written doc's from P-Eng's shown to me. Otherwise I take the lowest common denominator approach - the wall of the tube has to be the thickest spec for the lowest spec of tube...

We typically have spec's for ERW, DOM and Cmoly.

Brian

>

||What can't you use paint remover on a portion of the hoop and look for the ||weld HAZ?

I can do that

|| Is this a "I have to check one car, once", or "I'm SCCA Regional ||Tech and I have to check 100 cars all on the same weekend"?

This is in regard to a car I own, but I also wanted to know, since this is a new rule, how the average SCCA tech guy could enforce it.

||Since I'm in sort of the same business (CASC tech inspector), what ||certification is acceptable to SCCA? I have yet to be presented with any ||sort of certificate on the tube itself, but I have had written doc's from ||P-Eng's shown to me. Otherwise I take the lowest common denominator ||approach - the wall of the tube has to be the thickest spec for the lowest ||spec of tube...

Tube thickness is the same spec for both. In the past, the spec has been 1/4" larger OD tube for ERW, so in trutch they have had a need to be able to differentiate all along.

Texas Parts Guy

You can't depend on finding the HAZ and blueing on the tube. If you have some top quality ERW tube that was prepped for painting by sanding, it will be very difficult to find the seam of ERW. A Rockwell test can tell the difference between two samples (DOM is harder) but probably not good enough to

The SAE design competition's that I deal with require that the roll stucture be constructed of specificed material and backed up with a "Mill Certificate". This is the test report prepared with each batch of better quality tubing. It should have the tensile, yield, elongation, and chemical composition as a printout on mill letterhead. Stop at the local high volume steel distributor to see a sample copy of one.

You still have the issue of "is the tube on the vehicle the same stuff as the mill cert?" In the SAE competitions I deal with, there is a mandatory safety report that includes key structural details, the mill cert, and is signed by the team captan and the advisor. (Advisor functions as the PE in this case) At the competition, the safety report is pulled up, the inspector gets out an ultrasound probe and checks the cage where ever he feels like, and the job gets done.

How this would work in the other competitions is less clear to me. The incentive to cheat on it is substantial if you have already built the vehicle.

Your use of the lowest common denominator is a good policy.

If I were king for a day on this I'd probably go this route:

1) Specify DOM tube for all critical roll structures. 2) Design the diameter and wall rules so that using the slightly softer ERW will not affect the safety appreciably. If someone cheats, at least they don't get killed. They might save a few bucks but they won't gain a weight advantage. 3) Grandfater in the old frames for a certain number of years, depending on how long they tend to last. 4) Use a steel stamp (like on the O2 bottles) to put a date code the first time a roll hoop is used.

I have mixed emotions on specifying DOM for roll cages. I actually like high end ERW better because it is slightly softer, takes welds better (fewer HAZ issues) But DOM is a more uniform product from batch to batch and vendor to vendor. If I specify DOM, I get DOM. Good ERW is great stuff, bad ERW is trash.

As a side note: We used huge quantities of ERW chome moly. It was special ordered from our regular ERW mill, they just ran different strip stock through the mill. Cost was less than half of the cost of regular seamless Chrome moly. But I'll bet you would have no idea how to handle it in the rules book!

Brian wrote:

On Fri, 09 Jul 2004 14:57:16 GMT, snipped-for-privacy@REMOVEtxol.net (Rex B) calmly ranted:

They could simply say "Bring your rollbar (and any other) certifications with you to checkin or you don't race." Since it's their game, they set the rules. :(

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On Fri, 09 Jul 2004 15:15:07 GMT, RoyJ wrote:

||You can't depend on finding the HAZ and blueing on the tube. If you have ||some top quality ERW tube that was prepped for painting by sanding, it ||will be very difficult to find the seam of ERW. A Rockwell test can ||tell the difference between two samples (DOM is harder) but probably not ||good enough to || ||The SAE design competition's that I deal with require that the roll ||stucture be constructed of specificed material and backed up with a ||"Mill Certificate". This is the test report prepared with each batch of ||better quality tubing. It should have the tensile, yield, elongation, ||and chemical composition as a printout on mill letterhead. Stop at the ||local high volume steel distributor to see a sample copy of one. || ||You still have the issue of "is the tube on the vehicle the same stuff ||as the mill cert?" In the SAE competitions I deal with, there is a ||mandatory safety report that includes key structural details, the mill ||cert, and is signed by the team captan and the advisor. (Advisor ||functions as the PE in this case) At the competition, the safety report ||is pulled up, the inspector gets out an ultrasound probe and checks the ||cage where ever he feels like, and the job gets done.

Formula SAE?

||How this would work in the other competitions is less clear to me. The ||incentive to cheat on it is substantial if you have already built the ||vehicle. || ||Your use of the lowest common denominator is a good policy. || ||If I were king for a day on this I'd probably go this route: ||1) Specify DOM tube for all critical roll structures. ||2) Design the diameter and wall rules so that using the slightly softer ||ERW will not affect the safety appreciably. If someone cheats, at least ||they don't get killed. They might save a few bucks but they won't gain a ||weight advantage. ||3) Grandfater in the old frames for a certain number of years, depending ||on how long they tend to last. ||4) Use a steel stamp (like on the O2 bottles) to put a date code the ||first time a roll hoop is used. || ||I have mixed emotions on specifying DOM for roll cages. I actually like ||high end ERW better because it is slightly softer, takes welds better ||(fewer HAZ issues) But DOM is a more uniform product from batch to batch ||and vendor to vendor. If I specify DOM, I get DOM. Good ERW is great ||stuff, bad ERW is trash. || ||As a side note: We used huge quantities of ERW chome moly. It was ||special ordered from our regular ERW mill, they just ran different strip ||stock through the mill. Cost was less than half of the cost of regular ||seamless Chrome moly. But I'll bet you would have no idea how to handle ||it in the rulebook!

The existing rules allowing ERW in greater diameter was working fine. I'm not sure why they changed it, except possibly as the result of litigation that the membership is never privy to. I personally T-boned a car with an off-the-shelf Autpower ERW cage a few years ago. I was doing maybe 40 mph and hit the car square in the passenber door. The front of my car was trashed, the door of the other car was wrapped around and through the horzontal door bars of the cage, but the cage was not bent in any way. It probably helped some that the track was wet and traction was low.

Thanks for the input

|| || || ||Brian wrote: ||> What can't you use paint remover on a portion of the hoop and look for the ||> weld HAZ? Is this a "I have to check one car, once", or "I'm SCCA Regional ||> Tech and I have to check 100 cars all on the same weekend"? ||> ||> Since I'm in sort of the same business (CASC tech inspector), what ||> certification is acceptable to SCCA? I have yet to be presented with any ||> sort of certificate on the tube itself, but I have had written doc's from ||> P-Eng's shown to me. Otherwise I take the lowest common denominator ||> approach - the wall of the tube has to be the thickest spec for the lowest ||> spec of tube... ||> ||> We typically have spec's for ERW, DOM and Cmoly. ||> ||> Brian ||> ||> ||> "RoyJ" wrote in message ||> news:L_hHc.9806$ snipped-for-privacy@newsread1.news.pas.earthlink.net... ||> ||>>But that still doesn't get to the ERW versus DOM issue. ||>>

||>>nic wrote: ||>>

||>>>The answer is really simple, I think. ||>>>

||>>>NHRA uses an ultrasonic inspection device. ||>>>It is able to resolve variation in thickness down to a few ||>>>thousandths. of an inch. I believe that it will work through ||>>>paint, though with some loss of accuracy. It should be able ||>>>to pick up the seam of the tubing. ||>>>The regional technical folks may be able to help you or ||>>>suggest who may have the equipment to do it for you. ||>>>Here's the Southcentral chassis inspectors. ||>>>

||> ||>

||> ||>>>

||>>>Rex B wrote: ||>>>

||>>>

||>>>>I have a car with a rollcage installed when I got it. ||>>>>Racing organization rules now require DOM-only construction. ||>>>>Is there any way to tell what this cage is contructed from, without ||> ||> cutting it? ||> ||>>>>Texas Parts Guy ||> ||> ||>

Texas Parts Guy

The last event that I went to did just that. They started strictly enforcing a new for 2004 rule that had not been enforced at the 2 previous 2004 events. 117 vehicles registered, some driving 1500 miles or more for a 4 day event with an average team size of perhaps 5 people Perhaps 85% failed tech inspection. Fix involved getting some not very common parts air freighted in since the local maket could only supply enough for 20 teams or so. Picture 70 teams and 350 people sitting on their hands waiting for the next day shipment. It was very quiet on the test track. It was very noisy at the next rules committee meeting.

My team did fine, my team leader has a knack for being first in line. We had the test tracks pretty much to ourselves on day 2 of the event.

I have no real problem with the intent of the rules change, only in the way it was implimented. An e-mail saying that they would be enforcing it along with pictures of qualifing and non qualifiing parts would have made life so much eaiser.

Cheers.

Larry Jaques wrote:

And what would have been even better would have been for the inspectors to pass that that equipment for one or two events, but point out that the non-compliant part would not pass after such & such a date.

Something like that. Or just let it slide since this was the last event of this season, do it right next year. The organizers got an earfull from me and quite a few others.

Jim Levie wrote:

As a former SCCA/CART tech inspector, I'm wondering what the basis was for their judgment in the first place. The seamless/ERW debate was held in the late 1950s, and ERW won, all over the world. DOM wasn't an issue then; it was seamless or plain, unworked ERW.

So, what happened? Did some failures start to show up? Or was there one case, and, if one case, did it really show a weakness in welded-seam tubing, or simply a quality failure? Or have the suppliers of ERW slacked off on quality because they know DOM will be used for critical applications in most cases?

It sounds like somebody got a little overwrought. When I think of the things we used to let pass, this one sounds trivial.

Ed Huntress

Ed, I don't recall seeing any discussin, just a notice of a change in the requriement for 2004. Typically, when a construction requirement changes for a safety-related item, it's insurance/legal driven and no one at National will discuss it. And that attitude is a separate problem. Texas Parts Guy