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The Sky Is Falling, The Sky Is Falling!

By May 15, 2014September 3rd, 2014Destructs, Extrusion

Hold your breath silly chicken and listen for a moment before you come to any hasty conclusions! Did he just mark a destruct on an extrusion weld? This must be some form of CQA blasphemy! No one in his or her right mind would mark a destruct on an extrusion weld, especially a patch!

As a CQA monitor, I usually have the liberty in the specifications to mark destructs anywhere I suspect a poor quality weld may exist. While some specifications clearly mandate extrusion destructs, the look of astonishment is sometimes priceless when I do mark them—whether specified or not. Usually, I already have the latitude to mark them from the certifying engineer, which is always nice to have in your back pocket for the ensuing argument from the installer. But why argue if they are going to pass?

The most common argument, of course, is that you are creating larger holes in the geomembrane that are now being repaired with the proven lesser quality extrusion weld. And, it is a valid argument—I agree with everyone that minimizing holes in the liner is a good thing; however, I also believe that there needs to be a way of keeping people honest and accountable throughout the entire installation process, regardless of which position you are in or which team you are on.

And now my argument back to you, Mr./Mrs. Installer is that you agree the extrusion welding is a lesser quality weld, correct? And, the quality of this weld is heavily operator-dependent—from heat tacking, beveling, grinding, and ultimately the welding. I know your operator has passed a trial weld; but, haven’t all failing destructs you’ve ever seen (apparently fusion only, as you’ve never been on a project before where extrusion destructs were taken) been welded by an operator who passed a trial weld?

As if that isn’t enough to get some installers spinning, wait until they see how I can make all the pieces of a destruct fit on a 1’ x 1’ patch! So, now I am perceived as the bad guy on a witch-hunt who is out to get them—especially since the lab portion is typically not on the nice long straightaway weld that would be preferred from some points of view.

You see, while you may think I am out to get you, I am only trying to do my job in making sure the project is obtaining the highest quality possible.  Everyone seems to know that extrusion welds are where most of the installation problems will be, yet it is one of the most overlooked areas of the geomembrane installation. And, the destruct is not just about whether it passes or fails—it also gives the viewer a chance to observe the true quality of the weld from the underside for things nearly invisible from the top side. You can look for burn-through, especially at tee joints and stop/start overlap locations. Likewise, you can look for bevel, weld centering, grind depth; signs of weld stress like rapid cooling, and other indicators of problems with extrusion welds. There is a lot to be learned from looking at actual field extrusion welds that you simply cannot learn from a trial weld.

By having liberty to take extrusion destructs on most of my projects, I have learned quite a bit over the years. For instance, on one project, an extrusion operator routinely failed destructive samples—and this operator was quite seasoned and seemingly did everything right except pass destructs. Even the installer was baffled by this turn of events for this operator. Eventually, after going through the process of changing extrusion welder settings, changing equipment, and even several grinding operators, he came to where he never failed another destruct—and believe me, I tried! You see, one of the grinding technicians issued me a challenge by telling me that I would not get a failing destruct on him—and he was right! I congratulated him at the end of the project! The grinder operator made nearly all of the difference for this particular extrusion operator. We would have never known that without extrusion destructs and would have ended up with an inferior final product.

I said above that the grinder operator made nearly all of the difference—feedback was the other important ingredient (which I will discuss in greater detail on another blog). On this particular project, we had our own on-site laboratory, in which I performed a majority of the laboratory testing. As was the case with any sample I tested, if I had seen anything outside the norm, such as a trend getting slight peel, or lower strength, off-center welds, etc., I would have informed both the foreman and the welding personnel right away, so they could make adjustments if needed. I know on many projects, this feedback has proven invaluable to installers in reducing failures!

So, Henny Penny, while the sky is not falling, I will still leave you with a couple thoughts; so, please take a seat. Are you holding onto your chair? Here they come:

Why are extrusion trial seams not performed for teams (where any time a grinder operator is switched, a new trial weld is performed)? And, when will extrusion welds be scrutinized on a level commensurate with their lower quality?