Question about welding and heavy duty truck frames.

By Kix

Date 06-23-2008 12:46

You always see those "do not weld on frame" stickers on big truck frames, but why? What is it that makes them so difficult to weld successfully? Could it be hydrogen embrittlement next to the weld? I realize that this material is usually some type of steel that is quenched and tempered to give it the hardness and strength it needs to get the job done. I also realize that when you weld on it, it changes the desired characteristics of the steel therefor creating weak spots.
I've seen some frames welded with GTAW, SMAW, and GMAW without any prob, but I have also seen some welded that have cracked again near or next to the weld. For example, I saw a crack in a frame repaired with GTAW, it didn't even penetrate half way through the frame and it cracked right next to the weld. This was obviously in a stressed area and you would of thought that if it was going to crack again, that it would have cracked through the PJP weld and not next to it. Well, I would of though that anyway.;-) In that particular instance, I was thinking Hydrogen embrittlement. So do you think a bit of preheat, weld it with a low hydrogen electrode, a good interpass temp, and an annealing process done afterwards might have given a successfull repair? This kind of stuff really interests me and I love to know why things happen.

Ray C.

By GRoberts (***)

Date 06-23-2008 15:08

Well, for one thing, any weld is going to be a stress riser in a high fatigue situation. Never a good thing. Also, the rig manufacturer's can't control the way people weld to the frame, and half of the time, people would probably do it wrong, so I imagine that they would rather not take the chance. However, if you truly want to know if the steel is weldable, see if the manufacturer welded anything to it.

By 803056

Date 06-23-2008 19:57

The feds used to prohibit welding on truck frames up until about 2007 if I remember correctly. Then they changed their position and simply say that the welding must be done in accordance with the manufacturer's recommendations.

The problems include the fact that many frames are quenched and tempered steels that have heat input limitations. As you suspected, delayed cracking due to difusible hydrogen is also a concern.

The notch affects of partial joint penetration welds, weld discontinuities such as undercut, slag inclusions, incomplete fusion, etc. are a concern. The notch affects due to changes in geometry as well as metallurgical notches due to changes in grain size, hardness, tensile strength, etc. are also a concern.

Where the weld is located can influence the level of success experienced as well. Is the weld located in front of or behind the spring hangers? Is the weld subject to tensile or compressive stresses or a combination of the two?

What is the expected temperature range the weld will be operating in? Cold weather will have an effect of the notch toughness of the weld and heat affected zone. Any truck used to plow snow will experience impact loads at low operating temperatures.

The one thing I find interesting is that the feds do not require either the welder or the WPS to be qualified by testing. Anyone silly enough to take on the liability of welding on a truck frame when they don't even know what the nature of the base metal is free do so.

Best regards - Al

By DaveBoyer (*****)

Date 06-24-2008 02:31

The heat treated heavy truck frames made at Dana Corp's Parrish Frame plant were made from SAE 1027M. Cautions against welding are to prevent the manufacturer from being liable for somebody else's work. At Our plant fatigue tests were done on random production parts to insure quality, not on parts repaired by an outside party they have no control over.