Welding Failure -4130Steel Pipe

By Kix

Date 12-04-2008 17:56

Can you take pictures of the failure please? This would help out a lot!

By chandramouli Date 12-05-2008 23:40

Picture Attached

Attachment: WeldFailure.ppt (200k)

By bozaktwo1 (***)

Date 12-08-2008 01:17

It's difficult to tell from that photo, but my first guess would be that that the use of the lower carbon, higher silicon filler wire and the lack of control for the post weld heat treatment have caused considerable weakening of the heat affected zone (HAZ). Looking at that weld, I would guess that it was not laid in by an experienced hand, and perhaps a small defect, such as a toe crack or slight undercut created a stress riser, causing the metal to fail in the HAZ. Is that weld inspected before the equipment is placed in service?

By bozaktwo1 (***)

Date 12-04-2008 18:11

First of all, welcome to the forum! There are a lot of people in here who can share a wealth of welding knowledge.

Second, I am sure we would all like to know what code you're welding to. For instance, I can answer D1.1 questions, but I know next to nothing about ASME. Lots of other guys know ASME pretty well.

From my experiences with 4130, your choice of filler isn't the best. The ER70S filler is great for low carbon steels, like A36, but once you start going higher with the carbon and add the other ingredients that make up a high strength low alloy steel, you run the risk of making an extremely brittle weld along the toes, where the filler dilutes with the base metal. That's likely 90% of your problem right there. Try a filler made for HSLA steels, like ER80S or ER90S.

The rest of it probably has to do with the heat treatment. In this case (in my opinion), the heat treat at 600F isn't really doing anything. What is the purpose for the heat treat? Is it just a stress relieve operation, or for hardening? What is the soak time? Do you control the cooling, or just take the heat off and allow it to come down to room temperature? Another consideration: did you preheat the joint?

I hope I have helped a little, but I am curious about the heat treatment parts.

By chandramouli Date 12-05-2008 23:44

Basically I am plastics Engineer, SO I am not sure about the codes. The weld region is heated treated to stress releive. Cooling is not controlled, it cools to room temperature.

Thanks & Regards
Chandramouli

By Kix

Date 12-08-2008 13:41

NHRA uses ER70S-2 to weld all their chromoly chassis. They switched to an ER80S-D2 for awhile, but now they're back to ER70S-D2. 3 very common fillers for 4130 tube chassis are ER70S-2, ER80S-D2 and ER309L stainless for racing applications. The stress releaving operations are unknown to me for NHRA. I know the baja 500 guys that are using ER309L on their chassis do not post weld heat treat or stress releave.

By bozaktwo1 (***)

Date 12-08-2008 17:26

I don't know the stress relief numbers off the top of my head, but 600F seems a little too cool. Also, not too sure about the soak time; I would think at least an hour.

I have had success welding 4130 with 70s, 80s and of course 8018 and 9018 SMAW. I suspect that using the 70s wire in a joint with that much stress could be a contributing factor to the failure; of course I have been wrong before. Since the joint is failing in the base metal in the HAZ, the filler is probably not playing a role, unless it's just a question of dilution.

http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=60316;hl=4130%2c%20stress%20relief

By MBSims

Date 12-06-2008 16:23

It looks like the force tore the base metal on the vertical tube. The fracture probably started at the top at the toe of the weld. My guess is that the vertical tube is too thin to restrain the bending moment without flexing through the thickness of the tube. Just based on dead weight, there is a 900 lb/ft moment force at the connection. If the 300 lb. weight is being dropped, then there is an impact load that is much higher than 900 lb/ft. You might try increasing the wall thickness of the vertical tube and/or adding a gusset or brace on top.

By tom cooper (**)

Date 12-09-2008 19:40

Aside from possible design fault as mentioned, when welding 4130 or any Cr-Mo you need to preheat to at least 300 deg F. We use 400 deg F preheat and stress relief at 1100 deg F for 1 hr/inch. 80s or 90s is the correct wire to be using and to match the chrome, probably a B2 or B3 wire should be used. That is what we do and we work 4130 all the time.

By Tommyjoking (****)

Date 12-10-2008 16:23 Edited 12-10-2008 18:54

THX Tom......preheat and post treatment is too often ignored when working with this "problematic" material!!

Besides the aforementioned possible engineering issues regarding material selection ????? Experienced welders always overbuild/engineer one off or small batch weldments. A well welded part, discounting any heat treat / normalizing, correct procedure, design or not, will often fail right next to the weld as in your picture. PROVIDED the materials being used are substantial enough for the loads being imposed my guess would be: The actual picture of the failure makes me look to the post weld heat treat/Normalizing.....I suspect the HAZ was not restored properly. I know that preheat procedure can reduce weld defect significantly on 4130 tig welds...but I am unsure on its mechanical benefits outside the actual weld deposit besides helping slightly reduce distortion in fixtured weldments. Just my $.02 as I am no expert on mechanical restorative procedure with 4130.

Tommy

By bozaktwo1 (***)

Date 12-11-2008 02:13

I'm still waiting for the OP to tell us whether the joint was preheated. I'd bet a buck or two it wasn't. And 600F is just plain worthless as a PWHT for 4130.

My $.02 plus your $.02 = $dang near a nickel. :)