Arc Welding 101: Addressing linear porosity

Q: We are experiencing linear porosity at the furthest point of penetration when welding heavy plate. The porosity is 0.3 mm dia., but it occurs regularly in every weld we’ve sectioned so far.

We are using a semiautomatic spray transfer process with a 0.045-in. ER70S-6 electrode, and a shielding gas mix of 91 percent argon (Ar), 5 percent carbon dioxide (CO₂), and 4 percent oxygen (O₂).

A: I suspect that your weld penetration profile is showing “finger penetration,” or a real deep area of penetration at the weld root. At this location, the profile is much deeper than it is wide. This will cause the area to open up during solidification.

Grab your copy of AWS D1.1 and check out the commentary section at C3.7.2, “Width/Depth Pass Limitations,” and Figure C-3.2, “Examples of Centerline Cracking.”

I was asked to troubleshoot a similar condition during a job interview for a former employer. To save money, they had switched from a 0.045-in.-dia. electrode to a 0.052-in.-dia. electrode. The high wire feed speed (WFS) with the larger-diameter electrode created a considerable increase in current, which equates to deeper root penetration.

Like you, they had this pore everywhere they sectioned, which I believe was more of a linear void. Although not popular, reducing the WFS eliminated the problem. P.S. I got the job!

Reducing current (WFS) typically will reduce this finger penetration, which should remedy your problem. One other thing: Yours is a weird shielding gas mixture. I’m not sure why you would go with so much oxygen, but I don’t know your whole story. If you can, replace the O₂ with more CO₂. Perhaps that will change your weld profile as well.