Tuesday, April 19, 2011

Weave or Stringer?

Hi Paul,
I'm a big fan of "Practical Welding Today" and have recognized your input for quite some time. I have a very generalized and basic question for you about a weld situation we have, and I feel that you are more than qualified to give an opinion.

We build steel tanks mainly for containing hydraulic oil. The material is A36 picked and oiled and the gauge will range from 10 GA up to around 3/8".  We are using Lincoln 355M power sources, GMAW process, ER70-.035 wire and 90/10 gas. Almost all of the tanks are made with an overlap design vs. a corner to corner weld. This creates almost all fillet welds, mostly in the horizontal position, and a few in vertical. The question I have is, given this design and end product, do you feel it's appropriate to do a weave or a stringer bead when welding these? This is a big argument here right now. We used to allow weaving and we had great looking welds on our product with minimum leaks. Recently we have put a stop to all weaving and are demanding that all welders use straight stringer beads. Now we have welds that look very inconsistent and overall "poor".  We also have a great number of leaks which take a long time to repair and re-test. I know that weaving is NOT allowed in certain weldments, mainly when high strength steel like T1 is used, (Greater HAZ, slag inclusions, etc.). Do you think that on a simple product such as this when high strength is not an issue the weave method is acceptable? I don't believe the WPS for this weld states anything about weave vs. straight.

Please give me your opinion.

Thanks! Steve R.
Manufacturing Engineering Dept.

Hey Steve, Sorry for the delayed response. That 355m, do you use it in the Pulse or CV mode?  Also, your shielding gas and wire combination is going to tend to give you minimal sidewall fusion dependent on the mode of transfer used.  An increase in Co2 will tend to improve sidewall fusion.  It will also lead to increased penetration which could lead to burn through on thinner material.  That being said... Your joint design (Lap/Fillet) should lend itself, just fine, to Horizontal (2F) fillets using a stringer bead.  When weld size is increased (t>5/16) a multi-pass stringer technique should be utilized.  This is an application where I would never suggest a weave when manually welding. In the Vertical (3F) position the progression should be Up (vertical down with a process that minimizes sidewall fusion to begin with, is flertin' with disaster). This position lends itself to a weave technique. Keep in mind, I'm not talking about a "Whip" motion that constantly moves forward, then back.  We are talking about a side to side movement. As for the look of the weld... Don't let your personal opinion of what looks good cloud good judgement.  The welds should be acceptable, as determined by the code you use.  Liking the look of a weave better, as opposed to stringers, is a personal opinion.  I would suspect that if tomorrow I walked on to the shop floor where everybody used a weave and proclaimed, "Beginning this day and all future days the weave technique will no longer be an acceptable practice!", it would take some time before Welders got use to the new technique (could be months) and I would expect the welding to look inconsistent.