Multi-pass submerged-arc welding 3

[Metalguy]

We are performing a lot of multi-pass submerged-arc welding (SAW) of low-alloy steels (P3), and are getting too many small slag inclusions in the welds.

What would be the most likely causes of this: failure to remove all the burned slag from the previous pass, a problem with the angle/position of the wire with respect to the weld groove, or something else?

 

[CWIC]

There are a number of sources for the slag inclusions in your SAW welds. Your application is not a difficult one to weld with this process.

1.) The basic welding parameters (amperage/voltage/arc travel speed/wire feed speed) may be incorrect.
*Excessive arc voltage has been problamatic in flux removal for one of my clients.
*High travel speeds will trap flux before allowing it to melt.
*High amperages tend to trap slag were the molten pool "boils over" from the actual weld pool. This is also associated with high wire feed speeds.

2.) I am sure you have already determined the flux/electrode combination to be satisfactory for the application.
*The type of flux used is factor to consider as well as the storage of the flux makes a BIG difference (i.e.: high humidity, exposure to any moisture or contamination, etc.)
*The amount of flux deposited during welding can affect the weld quality as well. (Excessive flux deposition?)
*If the flux has been reclaimed, there could be a contamination problem.

3.) Technique would be considered such as work and travel angles, electrode extension, etc.
*Cast and/or helix in the wire has cuased the arc to wander within the joint on a few occassions causing trapped slag.
*The starting method used can be considered.

By the way, you did not mention if you are using semi-automatic or mechanized/automatic process control or if your using single or multiple electrodes which throws more possibilities into the equation. There are many sources for the discontinuity noted in your post, perhaps more details could help.

 

[Metalguy]

This is single-wire, not tandem arc.

The flux is kept very dry all the time-the shop is tired of me yelling at them. Voltage, current and heat input are fine. I will attempt to check the "boil over" weld pool-hadn't thought of this before.

I tried to give you a red start but the damn thing doesn't seem to work.

 

[sayee1]

Metal guy,
A few more questions: Where is the slag inclusions coming, I know you said it is interpass but is it near the side wall or towards the centre of the weld? What is the flux size distribution typically and what is the "flux burden" you are maintaining? Thickness of joint? preheat? interpass? Groove angle? These are again plates / pipes that would be in PWHT condition. Are you cleaning the scales/rust from the weld joint before starting the welding? Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[WayneBeng]

First thing I would check would be angle/postition. Having said that, You need to have your setting such that you get a slightly convex weld profile. One way of telling if your parameters are close is how well the flux peels off.

Electrode Stickout may have an influence as well. I find the closer you stick to 1" (25mm) the fewer problems you have.

If a round object, What diameter are you welding?

 

[Metalguy]

Sayeeprasadr,

Yes, the joints are very clean when they start-I inspect every one myself. I'll see if we can determine where the slag is located most. "Flux burden" is a new one for me-do you mean the amount of re-use? I'll have to find that out too. The groove angles are very narrow-just a few degrees. I forget just how many-will find out. These welds are about 160 mm thick, and preheat is maintained right around 150-160 deg C.

WayneBeng,

The profile is always slightly convex, and the flux litterally falls off well. I'll find the stickout amount tomorrow. The diameter of these shells is about 15'.

 

[sayee1]

Metalguy,
Flux burden is the amount of flux layer deposited and is usually linked with the stickout and the location where the flux is dropped onto the part being welded(In front of the arc etc.) This plays a more important role with inconel type of welding or when you get pock marks on the surface wherever the trapped gases are not being allowed to escape. Won't play so important a role with the slag inclusions. If you are welding a 160mm thickiness plate/pipe, with a narrow groove, then the welding parameters and the bead p-lacement are possibly the most important factors you have to fine tune to avoid slag inclusions. BTW what method of seam tracking are you using in such a case? and can you spell out the wire dia, I, V and travel speeds typically being used? Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[Metalguy]

I'm still gathering data, but it's starting to look like a wire/groove alignment problem. Seems the setup isn't rigid enough to keep the wire where it belongs. Lasers have been added for guidance, but we have to eliminate the side-to-side variance from the non-rigid setup.

 

[sayee1]

Good metalguy now that you seem to have pined down the problem, keep us posted of the results when you are through! Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[Welder1]

With narrow gap SAW the angle between one weld face and another on the deposited weld is critical. This is likely contributing to the slag entrappment issue you have, assuming root and cover passes are not seeing this problem.

If adjusting parameters won't solve the problem you may need to look at smaller weld deposits on the middle passes. This will thin the weld metal deposit on each pass and increase the included angle between subsequent weld passes. This will certainly help the slag entrappment problem. William Roth, PE, CWI