Repair of Forming Cracks in Structual Steel 3

[Hiserdude]

Can anyone tell me where I can find something to document the recommended repair for stress cracks in 5/8" A36 grade structual steel. The parts were formed and are showing stress cracks on the outside radius of the bend. I know that I have been told that you can repair these areas by welding the affected areas, but I have not been able to find any documented evidence that this is considered an acceptable method.

Thanks,

Mike Hiser

 

[BillPSU]

Hiserdude
Are the cracks running the length of the part along the radius or simply across the end of the formed section? If it cracked the length of the bend I would not use that part. Cracks across the thickness on the end of the part are normally not considered a problem.

A36 shouldn't crack along the length unless you are using a too small male punch .625 radius or smaller, or an undersize vee die smaller than 5", or higher strength material has been use such as a 50-60 ksi material, or the parts are formed along the grain instead of across the grain. It could be a combination of the conditions.

 

[Hiserdude]

BILLPSU

Thanks for your reply. The cracks are not the entire length of the bend. They vary in length from 1/8" to 1" in length, but are well represented along the surface. The punch radius used was indeed identified as being small. The issue that we are faced with is more to repair the surface so that there are no questions from our customer with regards to the strength or integrity of the part. We just want to be sure that welding to cover the cracks is an appropriate method.

Thanks.
Mike

 

[BillPSU]

Hiserdude
Cosmetically you can fix the problem with welding the cracks closed and grinding flush then when its painted nobody knows. Structurally I would like to know that the stresses in the corners are well within design limits as you will not know the penetration of the weld unless you completely grind out the crack and weld. If you have past experience with this particular part then let that be your guide.
The real question is how do you avoid this in the future. If this has been a recurring problem stronger measures should be used. Someone not changing the punch to improve time performance or not having the correct radius punch available due to the cost of the tool are both examples of people not wanting to do a quality job. Quality is built in not inspected in or repaired.

Bill

 

[gbent]

I would not weld without knowing the application and stresses. If you weld perpendicular to tensile stresses that are cyclic, your weld will cause cracking after some number of cycles. I don't know how long it will take, but it will happen. Guaranteed.

 

[plasgears]

Blend out the cracks to semicircular bottoms, and weld repair using a ductile version of the base metal. This will help avoid further cracking and damage in service.

 

[adrianviorel]

just hope the opinion of a elbow supplier could help: Usually, elbows are grinded up to elimination of any cracks. After this operation thickness must be not less then required one. If we cannot eliminate the cracks, elbows are simply rejected. Anyhow, ANSI B 16.9 and related standards are quite restrictive about this

 

[Widmanstatten]

Hiserdude,
You can not do anything else than welding for those cracks on formed parts, additionally you can not be sure whether you copmpletely removed or it remains over there provided you completely remove the crack as BillPSU said.

The important thing is to build up a system to prevent the future problems. This is a general problem if you are using a small punch to form the parts. I suppose you to bend the parts at a temperature to prevent cracking step by step (for ex. you start with 90 degree and increasing)

 

[XELR8]

I would grind out the crack until you got to the parent metal and then weld the void back in with a E7018 weld rod.

There are rolled radius limits for different steel thicknesses in ASME. I forget the paragraph number. You can use this information as a guide.

If the material cracks are from forming procedures you may want to use a thinner metal or increase the radius.

I would need more information about the geometry to make a conclusive evaluation.

 

[kbravo]

The Cracks that you are talking about are also due to the way the grain in the steel runs when you are forming it.. If you form aginst the grain it will not crack, but if you form the direction of the grain it will crack....., Your best bet is to Grind out the crack untill you reach parent metal, and reweld...Good Luck..