Low Hydrogen Electrodes

[99491]

I have a quick question.

I have only encountered jobs (tank building) where the shell plates are to be built using a E6010 filler and E6013 cap which has proved to be easy to use in the past. I am now working on a job where the client is demanding we use E7018 on the shell joints (root and cap). We are of course pre-heating and shielding well and radiography is not a problem however we seem to be experiencing alot greater distortion on the joints compared to the other procedure.

Can anybody explain why these electrodes cause greater distortion yet the current and weld speed is the same?

 

[Ron]

E7018 electrodes generally require higher current per size than either the E6010 or E6013.

Are you doing post-heat as well?

 

[99491]

No... Is post heat a requirement with E7018?

 

[Ron]

Not usually, but depends on the thickness of the part, number of passes, etc. If you're getting distortion, you might want to consider it or you might consider going to smaller electrodes and more passes.

 

[gtaw]

Distortion is proportional to the number of thermal cycles and inversely proprotional to the square of the thickness.

Higher strength steels that are required to be welded with low hydrogen electrodes are often thinner than their lower strength counterparts, thus the distortion experienced is greater. In other words, 1/8 inch thick plate will have four times the distortion expected with 1/4 inch thick plate, all else considered to be equal.

You can reduce the distortion by using fewer weld passes, i.e. larger electrode diameters and fewer weld passes. Weave beads with higher heat input will result in fewer weld passes and will heat the "through thickness" more uniformly than small stringer beads. The difference in temperature is the root of the distortion experienced. The more uniform the heating, i.e., less delta T, the less distortion will be experienced.

Best regards - Al