Variety of Experience Lends Itself to Mentorship: A Conversation With Duane Miller
Peer Perspective: Duane Miller, Manager of Engineering Services at Lincoln Electric
Duane Miller joins us to discuss mentorship, weld puddles, the benefits of using square HSS and more.
Q: Can you introduce yourself and tell us more about your current professional role?
My name is Duane Miller. My current title is manager of engineering services with Lincoln Electric. I’ve been with Lincoln Electric for 44 years, and I retire next month.
Starting in June, Miller will begin a consulting arrangement with Lincoln Electric in addition to introducing his own consulting company, Listen to the Steel.
Q: Describe your career path and how you gained your breadth of practical experience in welded connections as an engineer.
My career path was probably as direct as possible when you consider my educational background and professional experience. I went to LeTourneau University and received a double major in welding engineering and mechanical engineering. Then, I immediately joined Lincoln Electric after graduation.
The mechanical engineering background was very helpful in the role I would eventually have at Lincoln Electric. I first joined and went into the technical sales department, which was a wonderful starting point. I was there for eight years. I got to see all kinds of welding, from simple repair and maintenance to structural applications. I became proficient as a welder. There was probably not a week that went by that I didn’t come home with a few burn holes in my dress clothes!
Miller also has experience in Lincoln Electric’s application engineering department and engineering services where he worked with the late Omer Blodgett, celebrated author and esteemed welding engineer.
Q: What’s one notable HSS project you’ve worked on?
I’ve worked on many HSS projects. Actually, I have a particular passion and love for HSS. I like it because it’s almost always welded. Even the bolted connections usually have welding associated with it.
This goes back about 30 years, but one of my favorite projects was the Minneapolis Convention Center. LeJeune Steel put it up. I was involved with multiple phases of the project, including some of the basic connection design issues and the welding process selection. I recommended and LeJeune Steel used a self-shielded flux cored electrode to gain access to the T-, K- and Y-connections that were part of the dome structure.
Miller elaborates on the copper roof treatment supported with square HSS structures. Access for welding was difficult, he explains, and all welders had to pass the 6GR welding qualification test.
The reason I selected this as a notable project was because of the involvement in multiple phases. Usually I get involved with just a limited element of the project, but the Minneapolis Convention Center was more comprehensive — an A-to-Z, start-to-finish involvement.
Q: Do you have any tips to offer engineers of record or connection design engineers to create more effective and efficient welded HSS connections?
Number one: The decision of whether you’re going to use a round or rectangular HSS is a really big decision. Now, I don’t take any exception to round. It’s beautiful, but the connections are difficult to prepare. Round tubes require more complicated, saddle-like cuts. Lincoln Electric’s Vernon Tool division makes cutting systems to create those round cuts easily. Welding of these complicated cuts is more difficult. For square and rectangular tubing, saws can be used to make the planar cuts. It’s going to be easier to assemble square HSS trusses, for example. Don’t minimize that decision. My general suggestion is to encourage the use of square HSS over round HSS when the engineer is able to do that.
My second point is to consider complete joint penetration groove welds as the last option. There are many good weld options for HSS. The flare bevels and the flare V grooves that we get with square HSS are free. We don’t have to prepare those joints to receive weld metal. So that’s an advantage when we’re using square or rectangular HSS. Because we have close shapes, our concerns about one-sided fillet welds are minimized.
Miller emphasizes a final point: Always consider production issues like inspection. This changes the nature of the connection configuration. From a design standpoint, Miller says it’s more efficient to use the overlapped connections with the common working point when considering K intersections or K joints. From a production point of view, gap connections can be helpful because they allow for access to quality welding and inspection later on.
Q: HSS chord members are sometimes shown spliced with CJP welds on structural drawings. Do you have advice or considerations to offer regarding this detail, especially at the butted corners of the HSS?
We have two broad brush options. We have compression splices and tension splices. My first admonition would be to consider the loading and whether a CJP is required. It will likely be required for tension applications, but for compressive applications, it may not be necessary. Now, once we’ve decided we have a CJP, we need to consider those details since it’ll be a one-sided weld. The backing is probably going to be a steel backing. The prequalified joint details in D 1.1, the structural welding code, will use steel backing for the one-sided CJP groove welds.
Next, we need to consider how to get the backing in place, what to use for backing material, et cetera. There are some relatively new options in D 1.1. These options allow for backing that’s formed to fit inside the tube.
Let’s start with square tubes. You can put two C-shaped pieces of backing inside the tube, or you can put one formed piece of backing that has one seam. It depends on the circumference or perimeter of the tube. There are constraints on where the seam can be placed in the backing though. Sometimes, we’re fortunate enough to find HSS where one member slides inside the other. If we can’t do that, you can always cut a plug so it fits perfectly inside the tube.
Miller says when it comes to corners, they do not always need to be welded. If you have a tension splice, the preferred practice is for the welder to weld around the corner. They should start on the flat and weld around the corner rather than having starts and stops on the corner.
Q: Is there an HSS welded connection you have often seen require repair? If so, what is a practical solution to repair that welded connection?
I’ve seen repairs frequently when we have a very difficult connection in terms of welder access. I previously mentioned the preference for a gapped connection when we’re working on a K configuration. Overlapped connections or small-gapped connection details can be very problematic. It starts with difficult access for the welder and continues through difficult access for inspection.
If we’re repairing and removing a defective weld metal, restricted access is problematic. Getting a grinder into these locations can be very difficult. And then, of course, it has to be rewelded and reinspected. The most problematic conditions are large tubes with large member sizes yet limited overlap dimensions. A solution to this is making sure there’s a sufficient gap in the connections so that the welder and the inspector have the opportunity to do a good job. The design, however, must account for the localized stresses associated with the gapped configuration.
Miller explains that the phrase “access for welding” creates an image of whether the welder can physically get his or her hand into the joint and whether the welding gun and cable assembly and nozzle can be placed in the joint. He thinks a better question is: can the welder see the puddle?
Access means you can stick your arm in a joint and fly blind. You’re trying to weld without seeing the puddle. That never works. What we need to do is make sure there’s enough access for the welder to be able to see the puddle so that they can deposit the quality weld.
Q: One common question the Steel Tube Institute receives is whether it’s acceptable to weld to the corners of an HSS. This can be welding HSS branch members to an HSS chord member with matched width or welding a single axially loaded plate directly to the corner of an HSS column. Do you have any general advice to offer in these types of situations? Does preheating help?
Let me start with this: Preheating is not going to help. There are two fundamental issues here. One is simply the geometry associated with the corner of square HSS. The geometry is a little challenging for the welder. Welding on the flats is pretty simple. The arc is propelled along the length. That’s pretty easy for the welder to make, but carrying the puddle around the corner, maintaining the full-sized weld and moving on to the other flat takes a degree of skill.
Now for the second issue: If we don’t need the weld on the corner from a perspective of strength, there’s no need to make that more complicated weld. One of the examples listed was welding to an HSS base plate. In the shop, that column is going to be horizontal. It’s not standing up in the fab shop. The fabricator will have the welder make one weld on a flat, rotate the part maybe 180 degrees and put a weld on the opposite side, then rotate 90 degrees for the third side and 180 degrees again for the fourth side. If it’s not needed from a strength perspective, it would be easier to just leave the weld off at that location.
Miller discusses how cold working steel increases the yield and tensile and decreases the elongation and notch toughness. The corners of HSS represent local areas of material with different mechanical properties. Many industry professionals have expressed concern over reduced notch toughness. But Miller isn’t as concerned about this as others are, particularly for statistically loaded connections in warm applications, like many building applications.
But that’s prompted lots of concern about the fracture potential coming from welded connections onto the radius. And yet we weld on it all the time. I don’t think preheating will help in that situation. I previously mentioned that we get ready-made flare bevel, groove weld configurations and flare V groove weld configurations from the production mill. We weld on these corners all the time. If you get into a cyclically loaded structure or cold temperature applications, I think you’re concerned about investigating a welding on the corner, which is maybe more justified.
Q: Your contributions to authored publications and speaking engagements are very impressive. What’s the most rewarding part of being a speaker at these engagements?
I appreciate the positive comments from my peers. I’ve always felt like accolades from your colleagues are the most positive feedback you can get.
I enjoy sharing knowledge that’s been given to me and passing it along. I look at knowledge a little bit like inheritance. We get to own it for a while and then we pass it along. Mr. Blodgett, my mentor, taught me many things. I get to hold those ideas for a while and then pass them along.
I don’t think knowledge is something to be hoarded, but something to be shared. And I sense an obligation, a professional obligation, to share those things.
Maybe the most significant aspect of preparing materials, particularly for lectures, is rediscovering things I’ve forgotten. Oftentimes, I learn new things and I find it energizing. Learning new things is fulfilling and mentally stimulating. And I get a kick out of that!
Q: Do you have any closing thoughts you’d like to share?
I strongly encourage the readers to think of opportunities they have to mentor others, or for those looking for a mentoring relationship to seek one out. It will jump-start your career, and I’m grateful for the input many people have had into my career.
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