Tack Weld with rod bars.

Date 07-03-2005 03:02

At our training facility we tack weld in two ways.
First, tack welds are put directly into the joint.
Secondly. we used, what we call bridge tacks. They are 1/4" pieces of cold roll steel about 1/2 " long. They are put in the groove of the joint and tack to the walls of the pipe. As you weld around the pipe, then you remove them one by one. This method avoids any stop & starts in the root of the joint to any existing fused tack welds, which you would normally have.

By JCaprarulo (**)

Date 07-03-2005 12:53

Thanks a lot for your information.
Main problem what I've founded is about bridge tacks material and its dilution with base material inside groove or even outside upon base material.

By G.S.Crisi (****)

Date 07-04-2005 17:07

Then I suggest you to use, instead of rod bars (or bridge tacks), what in the States are called "strongbacks" and in your country (Argentina) "perros". Any piping foreman will know what I'm talking about. If not, let me know your fax number and I'll fax you a drawing.
I've used them extensively back in my days of erector engineer with no problem at all. Also, their use is allowed by the Codes (B.31 etc.), provided you apply the tacks with the same eletrode (rod or wire) type with which the weld will be done, and grind thoroughly the rest of the tack after the strongback (perro) has been removed.
Giovanni S. Crisi
Sao Paulo - Brazil
P.S. Did you like the "4 a 1"?

By JTMcC

Date 07-04-2005 19:18

I think it depends on your application. On inside process or power piping I think you'll see quite a few things welded on the pipe for fitup purposes. But in cross country pipeline work, where the pipe is and always has been considered sacred, even an arc burn on the pipe/fitting means a cutout. In that world you wouldn't want to suggest tacking bars across the joint.
I'd look closely into what is considered acceptable practice in your specific field, and go from there.

JTMcC.

By JCaprarulo (**)

Date 07-04-2005 20:09

Thank a lot Giovanni for your suggestion and I agree with you about "perro" being the more extendended fitup system in Argentina,except for pipelines, but my question is more related metallurgic considerations.
For example if you intend to use construction rod bars (very high carbon content), etc.
P.S. "3 a 1" game before like me much more.

By medicinehawk (**)

Date 07-06-2005 08:04

Here in New England, we have the policy: "You tack it- you weld it." When you have teams of fitters/welders, it is customary for the welder who tacks(the pipe joint) to go ahead and weld it using the procedure required for that systems application. I do alot of power piping where licensing (of the journeyman) is required as well as NDT of the pipe joint (usually radiographic inspection). Having this policy eliminates unneccessary whining because a welder will be responsible if he actually fit-up the joint and cannot blame anyone(but himself) if the weld should fail.
I don't care about the mechanical properties I am joining together (although I have been taught about all that)...the bottom line is that I have to trust whoever engineered the system I am working on, that the process I am using is right for the joint I am welding. If the WPS says use E-XXXs wire to weld the root & hot pass of a weld and XXXX for the balance.....then that is what I will use with a gap which also corresponds to the parameters set in the WPS. If things are done according to those guidelines then bridge tacks are not necessary and good welders can make tacks part of the weld and there should never be any issues regarding the soundness of the joint.
You want to know about fit-ups of joints? Send me an e-mail and I'll try and give you that information although there are documented sources where you can find that out, but the bottom line is that you have to follow the procedure required for that alloy.
Hawk

By JCaprarulo (**)

Date 07-06-2005 10:56

Absolutely clear your explanation, thanks a lot for it.

By medicinehawk (**)

Date 07-07-2005 08:21

NP.
Be well.
Hawk