Gas Metal Arc Weld in the field? 3

[osol]

I have a project where some field modifications are needed to an existing structure. I need to add some brackets to an HSS7x7 column. The brackets will need to be flare bevel welded and I have some pretty high demand forces. Table J2.2 of AISC 360-10 specifies effective throat thicknesses for flare bevel welds and it seems like I would only get sufficient capacity if I specify GMAW or FCAW-G welds. I am wondering if these weld types are practical/feasible for field modifications?

Any guidance would be helpful. Thanks!

 

[kingnero]

I don't know the context of this table, but I am having trouble with it. There is no problem getting to the throat you want.
Get someone who knows what he is doing. There are some risks associated with field welding, but this is a walk in the park for a good welding engineer.
Open arc welding is preferred when outside, windy, ... but so is mma/smaw. (Short-arc) gas shielded welding is also possible but will need protection from rain/wind. There are however some restrictions on the HSS, especially if it's cold formed.

 

[gtaw]

A word of caution, GMAW refers to globular, pulsed, or spray. If you welding positions include vertical, horizontal (grooves), or overhead, you will be limited to pulsed or short circuiting transfer, the latter not being prequalified.

You would most likely have to put up wind breaks to keep a breeze from blowing the shielding gas away.

FCAW-S may be a choice deserving some consideration.

Best regards - Al

 

[osol]

Al,

Thanks for your response. Yes my specified weld is vertical but unfortunately FCAW-S does not give me the needed capacity. Only FCAW-G and GMAW.

 

[kingnero]

The capacity is not dictated by the process. Apparently here it is, according to this standard, but I see no reason for this. Why wouldn't a multi layer fillet weld be an option?

 

[weldstan]

We regularly used FCAW-G in the field with CV power supplies. GTAW is also regularly used. Wind blocks are essential when wind velocity is 5 mph or greater.

 

[dauwerda]

osol, keep in mind that the effective throat shown in table J2.2 is for a flare groove weld that is filled flush. If your geometry allows, you can do a flare bevel with a reinforcing fillet weld over the top to achieve your required effective throat.

kingnero, the effective throat is dictated by the process for a flare bevel weld on HSS (for a prequalified weld). This is because you have a root opening of 0 at the root of the weld, the effective penetration into the root is dependent on which weld process is used.

 

[jdonville]

If there is some doubt that your weld will not have enough *PREQUALIFIED* capacity based on the process, would there be a way to test the weld (using a more common field process such as SMAW) after it is installed? Could you try non-production test weldments in that environment to ensure that SMAW (or some other process) gets you what you need?

 

[gtaw]

The weld size of a flare groove (bevel or V) is dependent on the welding process and the position. The limitation is reasonable considering the "groove angle" approaches zero as one gets closer to the point of tangency.

If the manufacturer is convinced a larger weld size is possible, they can qualify the procedure by welding a sample, slicing it and performing macro etch examinations to verify the weld size achieved.

The strength of the weld is a function of the tensile strength of the filler metal and the limitation imposed on the allowable unit stress in both shear and tensile of the base metal being welded.

Granted, some welding processes are "hotter" so they produce more penetration as reflected in the table cited. However, the GMAW transfer modes conducive to welding in the vertical position have limited heat input or the molten metal would run down the welder's pant leg!


Best regards - Al

 

Field GMAW won't pass wind test.
Sorry.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[gtaw]

One must consider the definition of a field weld. The designation of a field weld simply means the welding is performed in a location other than the original shop, i.e., shop welding.

I've been on many projects where the "field" welding was performed on-site where there where four walls and a "roof" totally enclosing the area where welding was being performed. For all practical purposes they were welding in a "field shop". Wind, breezes, rain, snow, etc. was of no consequence, but still, it was considered field welding.

Best regards - Al

 

[ronsimpson]

This weld, made with GMAW, has no smut on the weld itself, clearly visible cleaning lines, and a little smut outboard of the cleaning lines.
All welds, whether produced with GTAW or GMAW, should be bright and shiny, with no gray or black coating on the weld itself. You also should be able to see a shiny cleaning stripe, about 1/16 to 1/8 inch wide, on either side of the weld. These cleaning stripes indicate the area where the reverse-polarity GMAW arc-or the reverse-polarity portion of an AC GTAW arc-has removed the oxide coating cathodically from the aluminum during welding.
It's OK to have a small amount of smut on the parent material outboard of the cleaning stripes. It's also common to see smut at starts, stops, and at corners. However, if the entire weld is coated with smut, you've done something wrong.

welderreview.com

 

[gtaw]

I see you mentioned aluminum in your post, but I don't see that it is relevant when welding carbon and high strength low alloy steels.

Best regards - Al