MIG with positioner. (Root Pass)

Date 02-28-2011 17:34

It might help you if stated 'why' you had to stop, grind, and restart. Weld too large when you go over it? Lack of penetration as you go over it? Other problems?

Can you grind the tacks down some before the welding begins so you could just keep going?

I presume you are using GMAW short circuit transfer since you are using 75/25 Ar/CO2. It would be a little difficult to get a smooth weld over existing tacks with that transfer mode.

Have a Great Day, Brent

By kidblue (*)

Date 02-28-2011 18:17 Edited 03-01-2011 17:11

Brent,
Yes, I'm using short circuit transfer and we are having lack of fusion, even when before start welding the tack weld have been grind. The wire is ER-70S-6 0.035" on a 6" sch. 40.

Ron

By welderbrent (*****)

Date 02-28-2011 19:18

Is your work required to meet any particular code? Say API 1104 since you are working short arc on pipe? Shouldn't be to D1.1 unless you got your process qualified by testing.

Have a Great Day, Brent

By kidblue (*)

Date 02-28-2011 19:55

Mostly we work with ASME B31.1 or B31.3. My client now is the Fed. Gov. and we will install a mechanical room with a chilled water system. We have the National Certified Pipe Welding Bureau (NCPWB) pre qualified welding procedures.

By Lawrence (*****)

Date 02-28-2011 20:18

My first thought would be to increase travel speed and WFS toward the top of your range, as well as inductence to closer to maximum. Assuming that your GMA welds are done at top dead center, 1G with rotated pipe, on your new setup.

If the tacks are feathered out, a good hot root pass should provide full penn on the back and a flat to slightly concave face, while melting into your tacks with no lack of fusion. With the added control and consistancy (assuming good fit-ups) of your new system, you should be able to go much hotter and faster than when you were doing the joints manually.

Tell us more about your parameters and fitup...

Voltage
Wire feed speed
Root opening
Root face
Travel Speed
Postion of weld

By Milton Gravitt (***)

Date 03-01-2011 15:54

Have you given any thought about GTAW tack-up and making a small tack. Now on the GMAW you have stay out in front of your puddle to make sure you are burning the edge off,because if you get on top of the puddle it will show lack of fusion. Just my thoughts.

M.G.

By kidblue (*)

Date 03-01-2011 21:33

I wasn't at the shop today, but as soon as I get there I will look over the machine settings.

By js55

Date 03-02-2011 13:32

Milton hit it on the head. You will never really be happy, at least in my experience, with GMAW roots and a Bug-O unless you go to GTAW tacks and reduce the size of the tack. Then you can feather edge and run 360. You will still have a start tie in problem you will have to deal with.
Our solution was to semi auto the root and then use the Bug-O for FCAW.
One tip however, if you tack with GMAW run a root in opposite quarters and then grind all four tacks at the same time. That way you only have to stop once for grind.

By kidblue (*)

Date 03-10-2011 19:46

Thanks!, we just received the Bug-O and start to make some runs over the bevels. I guess it take some time to do something descent. Other thing is, I change the 75-25 to 100 CO2 I should have better penetration. I keep posting.

By joe pirie (***)

Date 03-10-2011 21:05

use to run a ton of gmaw on pipe using a positioner. you dont have the gun at 12.00 for the root pass
we ran it at about 2.00 knife edge 3/16 root opening. I f you have lack of fusion going over tacks perhaps
the tacks were put in incorrectly . if your not going to grind out your tacks the tacks must be put in properly with
good penetration. We always stopped before the tacks and removed them did thousands of welds with ver little xray repair
you weld over bad tacks you'll get a bad weld