http://www.arc-zone.com/blog/joewelder/2009/01/08/metal-of-the-month-chromoly/ Wed, 18 Apr 2012 17:35:41 +0000 hourly 1 http://wordpress.org/?v=3.3.2 http://www.arc-zone.com/blog/joewelder/2009/01/08/metal-of-the-month-chromoly/comment-page-1/#comment-8417 Don Hesprich Thu, 22 Jul 2010 18:12:51 +0000 http://joewelder.com/?p=236#comment-8417 Dennis, I have the same problem. The SFI states that if mild steel is used on a chassis, it has to be 0.120 wall min. If the car was ever certified, then any material on the car that is less that 0.120 wall is more than likely 4130. Any material in the roll cage area (on my Front engine dragster, from the motor plate back) that is less that 0.120 wall and is MIG welded needs to be removed. Currently I am completely replacing the back half of the car because mild steel was welded to 4130 with MIG. This might be fine in everyday use, but will not certify. I check tubing wall by drilling a 1/8 hole away from any weld. Then I take a piece of 1/16 welding rod that I have bent at 90 degrees and stick it in the hole. With the bent part of the rod held tight against the inside of the tube wall, I mark the outer wall of the tube on the rod with a scribe. I remove the rod and can measure the wall thickness. This method gives you a fairly accurate answer. When I did this on the dragster, the shoulder hoop was 0.049 wall. It was probably 4130, but that is still too thin for the SFI 2.6 Certification. Get the appropriate SFI spec. from http://www.sfifoundation.com/. This will help determine what you have to replace. If you have any doubt, replace it. It is better to be safe the have something break loose when your upside down at 150 MPH. Good luck Dennis, I have the same problem. The SFI states that if mild steel is used on a chassis, it has to be 0.120 wall min. If the car was ever certified, then any material on the car that is less that 0.120 wall is more than likely 4130. Any material in the roll cage area (on my Front engine dragster, from the motor plate back) that is less that 0.120 wall and is MIG welded needs to be removed. Currently I am completely replacing the back half of the car because mild steel was welded to 4130 with MIG. This might be fine in everyday use, but will not certify.
I check tubing wall by drilling a 1/8 hole away from any weld. Then I take a piece of 1/16 welding rod that I have bent at 90 degrees and stick it in the hole. With the bent part of the rod held tight against the inside of the tube wall, I mark the outer wall of the tube on the rod with a scribe. I remove the rod and can measure the wall thickness. This method gives you a fairly accurate answer.
When I did this on the dragster, the shoulder hoop was 0.049 wall. It was probably 4130, but that is still too thin for the SFI 2.6 Certification.
Get the appropriate SFI spec. from http://www.sfifoundation.com/. This will help determine what you have to replace. If you have any doubt, replace it. It is better to be safe the have something break loose when your upside down at 150 MPH.
Good luck

]]> http://www.arc-zone.com/blog/joewelder/2009/01/08/metal-of-the-month-chromoly/comment-page-1/#comment-1884 Dennis Thu, 22 Jan 2009 18:27:33 +0000 http://joewelder.com/?p=236#comment-1884 I am working on a racecar (nhra) and the rollcage is supposed to be chromoly. Some of the car appears to be tig welded, but the rest mig. How can I figure out the material with out spending big money on a ultrasound meter. I am working on a racecar (nhra) and the rollcage is supposed to be chromoly. Some of the car appears to be tig welded, but the rest mig. How can I figure out the material with out spending big money on a ultrasound meter.

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