Welding A572 Gr 50

[Steelforbrains]

We are welding 3 rings together. One ring is a 1"x8" flat bar rolled the easy way to an 82 3/4" ID. The other two rings are 1"x5" flat bar rolled to a 82 3/4" OD. The rings are to be welding into a c channel shape with a full penetration single V-groove corner joint on each end of the 8" plate (resulting in an 8"x6"x1" channel rolled flange in) Every 10" we will be stitch welding a 3/4"x5"x6" plate inside the channel to brace the flanges. We are using a FCAW-G process with C25 shielding gas and an E71T-1 electrode. All plates are A572 Gr 50. My AWS charts recommend a 50 F preheat for this thickness. My questions are:
1) Should I be using a higher preheat since my joint is highly restrained?
2) What is the best way to measure my preheat?
3) Do I need to monitor my interpass temperature?
4) What diameter wire should I be using?
5) What is the largest weld that I can make in a single pass?

After this piece is welded it will be welded to the outisde of a cylinder mesuring 72 3/4" OD by 60" long and 3/8" thick. The cylinder is A36 steel. I plan to use a 45 degree single bevel groove weld to form a T-joint between the cylinder and the 1"x5" plates, with a 1/8" root face and and no root opening. I plan to use the same wire and gas.
6) Do I need preheat for this weld?
7) Should I stress relieve the assembly after welding?
8) I also want to machine the outer face of the 1"x8" plate to true it up with the cylinder. Then I want to case harden the outer surface. What is the best way to case harden this piece (flame, induction, other)?
10) How much hardness can I expect out of this material/how deep?

I know that is a lot of questions but I appreciate any help I can get.
Thanks.

 

[metengr]

Steelforbrains;
I can tell from your questions that you obviously do not have a qualified weld procedure for this job, and from my perspective this would seriously concern me. A 572 is a high strength low alloy modified structural steel. A-36 is structural steel. Have you sized your welds properly for this application? Do you intend to perform nondestructive testing after welding?

The answers provided below will not be all inclusive, and you should seek professional assistance in developing a suitable welding procedure specification for this job.

The following below should answer most of your questions;

1. I would recommend a minimum preheat of 150 deg F for all welding.

2. Preheat should be verified with Temp sticks or a portable contact pyrometer to assure preheat and also to monitor maximum interpass temperature.

3. You need to establish a maximum interpass temperature to minimize distortion during welding, and to avoid adverse effects on base metal toughness for the A 572 material from too much heat input.

4. Yes, I would recommend a post weld heat treatment after all welding is completed to reduce harmful residual stresses from welding for this application.

Get some professional help in assuring proper design of the welds (size) and development of a qualified welding procedure using the suggested base materials.

 

[BillPSU]

Another process problem for this kind of part is that you will have to stagger the weld around the part avoiding the weld pull. You will have to do sections of weld on alternating sides of centerline and probably on alternating sides of the ring to avoid excessive weld distortion.

 

[Goahead]

With reference to your requirement to case harden, it would not be an easy thing to do.
Flame and induction case hardening depend on carbon content of the steel. Low carbon steel would not harden appreciably.
Resorting to carburizing requires a large carburizing furnace.
Quenching from austenitizing temperature is not an easy feat for those dimensions, and distortion is likely to be important.
Depending on the actual requirements of your construction, if you need only certain surfaces hard, maybe thermal spray or hardfacing would provide the hardness you want.

http://www.welding-advisers.com/

 

[JoeTank]

I have designed many built-up structural rings of various configurations. Normally I use such rings in the design of large diameter storage tanks, bins and silos. Never have I had to use full penetration welds to join the components. Double fillet welds normally suffice for my applications. Can you re-evaluate the need for such heavy welds?

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com