Modern Steel Construction • June 2021 • Accelerated Welding: Part One

Duane K. Miller, Pe, Curtis L. Decker, SE, PE, PHD, AND MICHAEL S. FLAGG 2021-05-07 06:42:05

Taking on the need for speed in welding applications.

AISC IS IN THE SECOND YEAR of an unprecedented six-year plan to increase the speed at which a steel project is designed, fabricated, and erected.

The goal is to increase the speed of delivery of a project by 50% by the end of 2025. Dubbed “Need for Speed” (or N4S), this initiative is examining all elements of the steel design and construction process, optimizing each step in a way that gives the owner a completed project more quickly.

In some circles, this concept is called increased “throughput” or an increase in “the amount of material or items passing through a system or process.” In terms of N4S, the “item” is a building or bridge, and the “process” includes all of the design, detailing, fabrication, erection, and inspection activities.

The key metric behind N4S is, of course, time, and the goal is to reduce the time, from the start of design to delivery of a completed project to the owner. On the surface, this may seem like a renaming of “cost reduction” activities or “production enhancement” efforts—and in some ways, it is. However, N4S adds a new twist. Since the goal is to reduce the overall time of the delivery process, individual steps in the process may be more costly but result in an overall increase in throughput. This necessitates some changes in thinking.

Welding is a critical step in the steel construction process. In this article, twelve concepts are presented to reduce the time associated with such operations—and twelve more in a follow-up article. No one concept is a game-changer, but collectively these steps can contribute to the overall N4S goal.

A caveat: Each of the 24 concepts presented in these two articles is worthy of a full article, so additional investigation into the details of each one will be required. Nevertheless, these ideas will help anyone start to reduce the time associated with welding-related operations, whether your primary focus is on meeting the N4S goal or simply looking for ways to reduce costs and increase efficiency.

The 24 ideas are assigned to four broad categories: minimizing weld volumes, minimizing welding time, minimizing nonproductive welding-related activities, and minimizing weld quality problems. Six concepts are provided in each category.

The first category focuses on reducing the amount of welding required. Designers, detailers, fabricators, and erectors can all assist in achieving this goal.

Concept 1. Specify the smallest weld size possible, consistent with design requirements. The concept is simple: If a ¼-in. fillet weld is sufficient, specify ¼ in. If a PJP (partial-joint-penetration) groove weld is acceptable, do not specify a CJP (complete-joint-penetration) weld.

Consider this example: Using a 0.045 in.-diameter gas-shielded flux-cored arc welding (FCAW-G) electrode with optimized welding procedure specification (WPS) parameters for making a 5∕16-in. fillet (520 in. per minute, or ipm), the weld in Figure 1, Part a, was made with a travel speed of 11 ipm. In Part b, using the same electrode with an optimized WPS for a ¼-in. fillet (400 ipm), the travel speed was 13.5 ipm, with an increase in productivity of 17%. The time to make each of the welds in Figure 1 was the same. In this case, the productivity increased even though the smaller fillet weld was made with a lower wire feed speed than was the larger weld.

Mature specifications and codes, like the AISC Specification for Structural Steel Buildings (ANSI/AISC 360, aisc.org/specifications) and AWS D1.1 (www.aws.org), have dependable design criteria for the capacity of various weld types. There is no need for designers and detailers to specify larger than necessary welds “just to be safe.”

Concept 2. Fillet welds versus PJP groove welds: Make the right choice. Both fillets and PJP groove welds can be used in tee joints, so which one is the right choice? For the same weld throat dimension, PJPs require half the metal as do fillet welds, giving PJPs an edge. However, PJPs require time-consuming beveling options ahead of the welding operations.

Two rules of thumb are helpful. First, if the weld can be made in a single pass, fillet welds are nearly always faster to make since they do not require beveling operations. Second, when the required weld throat dimension exceeds ¾ in. (which equates to a 1-in. fillet leg size), a PJP will likely be completed faster than a fillet.

Figure 2, Part a, shows a ¼-in. PJP on each side, while an equivalent strength fillet weld (5∕16-in. each side) is shown in Part b. In this case, the fillet weld is the preferred option.

In contrast, Part c shows a 11∕16 in. PJP weld on each side while part d shows equivalent-strength fillet welds (1½-in.). While the 2:1 ratio of weld volume remains the same as the weld sizes increase, the cost to bevel for the PJP remains fairly constant and the extra passes required to make the fillet weld greatly increase the time of production. For large weld throat dimensions, PJPs can be made faster than fillet welds.

Concept 3. Select optimal groove weld geometries. Everyone knows that double-sided CJP groove welds require half as much welding as is required for single-sided CJPs, a 2:1 difference, right? Figure 3 seems to make this concept clear. But this figure is misleading, despite the common use of such illustrations. More thinking is needed, and detailers should be aware that some well-established ideas are simply not true.

Consider the two prequalified groove weld details for a 2-in. plate, as shown in Figure 4. The single-sided prequalified detail (B-U2a) in Part a has a 3∕8-in. root opening and 30° included angle, requiring 6.54 lb of deposited weld per ft. The double-sided option (B-U3b) in Part b has no root opening and a 1∕8-in. root face, requiring 5.37 lb per ft. While the double-sided option requires less weld metal, the difference is not the 2:1 ratio as implied by Figure 3; the actual ratio, in this case, is 1.22:1. The single-sided CJP will likely be the faster, more economical choice because the single-sided joint can be more quickly prepared (i.e., less flame cutting time) and does not require time-consuming plate handling to reposition the work for flat position welding.

The joint details need to be evaluated case by case, considering not only weld volumes but also joint preparation costs, material handling costs, the costs of backing and backgouging, and other factors. In some cases, increased throughput is achieved with single-sided details that require more welding but fewer associated activities.

Concept 4. Optimize joint fit-up. AWS D1.1 provides “as detailed” and “as fit” tolerances for prequalified joint details. For many fabricators and erecters, so long as the actual fit-up is within the “as fit” tolerances, life is good. But how do fit-up tolerances affect fabrication and erection speed?

Consider a typical field-produced beam-to-column connection, as shown in Figure 5. Part a shows a prequalified groove weld detail (TC-U4a-GF) with a 3∕8-in. root opening and 30° bevel angle. Using the AWS D1.1 tolerances, the root opening could increase to 5∕8 in. (Part b), and the bevel angle could increase to 40° (Part c); these permitted tolerances increase welding time by 38% and 20%, respectively. Increasing both dimensions to the maximum permitted increases welding time by 58% (Part d).

While poor fit-up is often viewed as a problem caused by the welder, many of these problems originate on the cutting table. Collaboration between the fabricator and erector is encouraged to gain a mutual understanding of how speed can be maximized by minimizing excessive fit-up dimensions.

Concept 5. Make welds of the proper size. Concept 1 is directed toward designers and detailers. Concept 5 concept is directed toward fabricators and erectors. The idea is simple: Make the weld size required on the drawings.

AWS D1.1 allows for up to 10% of the length of a fillet weld to be undersized within certain limits (see D1.1:2020, Table 8.1, item 6). There is, however, no allowance for the whole length of a weld to be slightly undersized, which is unfortunate. As a result, welders routinely make welds that are slightly oversized to avoid the probability of rejected welds. A slightly oversized weld does not significantly reduce speed, and generously oversized welds needlessly slow welding operations.

Consider the 5/16-in. fillet welds shown in Figure 6. An ideally sized, flat-faced weld is shown on Line a; such a weld is impractical to make in production on a repeated basis. The weld on Line b has legs that are oversized by 10%, with 1/16 in. convexity. Line c shows a 5/16 in. fillet, with legs oversized by 1/16 in., whereas Line d shows a 5/16-in. fillet, oversized by 1/8 in.; both have 1/16 in. convexity.

If the slightly oversized and slightly convex weld (Line b) is considered the norm, then speed is decreased by 17% when the weld on Line c is made. Speed is decreased by 56% when weld d is made instead of weld b.

While a flat-faced, perfectly sized fillet weld (Part a) is an unrealistic expectation of a semiautomatic welder, it is not unreasonable for a robot. A comparison of weld b to weld a suggests a productivity increase of 45% should be possible when robotic welding is used.

Concept 6. Limit backgouging on double-sided CJP groove welds. Prequalified CJP groove welds require backgouging to sound metal before the root pass on the second side is made. It is essential that the backgouging be complete; failure to backgouge to sound metal will typically result in defects in the weld root.

The air arc gouging (AAG) process is capable of removing metal 10 to 20 times faster than typical welding processes can deposit metal. When welders become too aggressive backgouging weld joints, it is easy to over-gouge the joint, creating unnecessary time-consuming work downstream. Unfortunately, it is often the most quality-conscience welder who does this, just to ensure a fully backgouged joint.

Consider the example of the 2-in. joint in Figure 7. In Part a, an optimal backgouge is used, removing metal to 1/16 in. beyond the incomplete fusion. In Part b, the backgouge is ¼ in. deeper than necessary. The result of the excessive backgouge is an approximate 25% decrease in speed.

Two practical suggestions are offered to limit this tendency. First, the selected carbon size (diameter) and current (amperage) should be appropriate for the amount of backgouging that is expected. For example, a root face of 1/8 in. will not need the same amount of backgouging compared to a root face of ¼ in., and the gouging parameters should be adjusted accordingly. Second, after initial backgouging, grinding can be used to complete the operation; grinding is usually easier to control and will naturally limit the tendency to remove more metal than is needed.

Also, keep this rule of thumb in mind: The time to restore the removed metal will be 10 to 20 times more than the removal time.

The second broad category involves reducing welding time. This is, of course, the traditional focus of most cost reduction/ productivity improvement activities, and much has been written on this topic. Here, the concepts presented are specifically directed at the fabricator and erector wanting to increase throughput.

Concept 7. Process selection: universal versus optimized. In many ways, structural steel fabrication facilities are big job shops; the nature of the work changes continually, and the exact nature of some steel configurations may never be seen again. The same could be said for erectors. The typical contractor is drawn to welding processes that are flexible, allowing them to deliver welds of the required quality on an everyday basis. It may be, for example, that submerged arc welding (SAW) may be ideal for a specific application, but the shop’s standard process of FCAW-G may be used just to keep things simple. That decision may be best, given the various facts that need to be considered, including capital investment, welder training, WPS development, welder qualification, etc.

On the other hand, the cost of such decisions should be recognized. Consider a typical shop situation: 5∕16-in. fillet welds made on a plate girder. If tandem SAW is used on a gantry with two sets of welding heads traveling at 40 ipm, then two web-to-flange welds on a 100-ft girder can be made in 30 minutes. Once the start button is pushed, there is no need for the welding to stop, and one operator can oversee the two sets of welding equipment. Remember that two welds are being considered for a total of 200 ft of welding in this example; the plate girder would likely have four such welds for a total of 400 ft of welding.

Compare that to a situation with four welders, each using 1∕16- in. diameter FCAW-G, making 5∕16-in. fillet welds, each with a travel speed of 18 ipm. The welders could be distributed along the length of the girder. In the same 30 minutes that the two welds could be made with tandem SAW, the four semiautomatic welders would make only 45 ft of weld, providing each welder kept the arc lit 25% of the time.

In this example, the use of an “optimized” welding process (tandem SAW) versus the “universal” process (FCAW-G) increased productivity by over 300%, even though four welders were engaged in welding with the semiautomatic alternative. For reasons like these, most fabricators have gantries or welding tractors that may be idle a good part of the year but become invaluable when a girder job arrives.

Next, consider a field application. Most erection projects will require both “in position” welding (that is, flat or horizontal) as well as “out of position” welding (vertical and overhead). With self-shielded flux-cored arc welding (FCAW-S) being the process of choice for field erection, one option for erectors is to have two wire feeders on the job, one with a high-productivity down-hand electrode and the second equipped with an electrode for all-position welding.

There is a second option that is simpler: Use one wire feeder for the whole job, incorporating an all-position electrode for all welding. While this may be a good choice, particularly for small projects, the production consequences need consideration.

Visualize a column splice of a W14×211. The two flange welds would require about 20 lb of weld metal. If made with FCAW-S and a 5∕64-in. E70T-6 electrode at a deposition rate of 11.5 pounds per hour, the total arc time would be about 1.7 hours. At an operating factor of 25%, it would require about 7 hours to complete.

An erector may alternately select an all-positon electrode, such as 0.072-in. E71T-8 with a deposition rate of 5.4 lb per hour. Arc time becomes 3.7 hours and the total time with an operating factor of 25% would be about 15 hours to complete the two flanges. A speed increase of 110% is achieved when the optimized electrode versus the universal electrode is used in this example.

Many fabricators have a standardized shop electrode size, typically 0.045-in. FCAW-G. The flexibility on a single electrode cannot be disputed, but the productivity implications are often overlooked. Consider the two welds made in Figure 8, both 5∕16-in. horizontal fillets. Each sample represents one minute of welding. The weld in Part a was made with the 0.045-in. electrode at a travel speed of 13.5 ipm, whereas the more optimal 1∕16-in. electrode made the weld in Part b at a rate of 18 ipm, a productivity increase of 33%.

To make it easier to use two electrodes, dual-headed wire feeders, as shown in Figure 9, provide the necessary production flexibility while minimizing the need for additional power supplies and the clutter of multiple wire feeders on a shop floor.

Concept 8. Optimize WPS parameters. According to AWS A3.0: Standard Welding Terms and Definitions, a WPS is “a document providing the required welding variables for a specific application to assure repeatability by properly trained welders and welding operators.” To many contractors, a WPS is a document whose primary purpose is to keep the welding inspector happy. Properly used, however, WPSs are important productivity control tools.

Small changes in welding parameters can significantly affect productivity. Consider the simple 5∕16-in. fillet welds, each made with the same process and same electrode, as shown in Figure 10. Each assembly represented one minute of welding. The weld in Part a was made with a 0.045-in.-diameter FCAW-G electrode, with a wire feed speed of 450 ipm and a travel speed of 9.5 ipm. In Part b, the weld was made with a wire feed speed of 520 and a travel speed of 11 ipm, or a 16% increase in productivity. The difference in productivity was achieved simply by using optimized parameters, which should be listed on the WPS.

Concept 9. Limit WPS variable options. Figure 11 contains the welding variables as listed on a recently reviewed WPS. The electrode diameter used on the project was 5∕64 in. (even though the WPS listed three different diameters). Five sets of amperage and voltage values for the 5∕64-in. electrode were listed; no travel speeds were shown. The welding parameters were taken from the filler metal manufacturer’s product literature, which is a good starting point. The WPS allowed the welder to use wire feed speeds from 90 to 240 ipm, with welding currents ranging from 210 amps to 380 amps.

The application involved a column splice of a W14×257 with a flange thickness of 17∕8 in. Each flange splice requires 8.6 lb of weld metal. If the welder selects to use a wire feed speed of 90 ipm, then the weld requires 71 minutes of arc time to weld one flange. On the other hand, with a wire feed speed of 240 ipm, one flange requires 27 minutes of arc time. This is an increase in productivity of 167%.

WPSs should list welding parameters that are specific to a given application as opposed to the general parameters supplied on the filler metal spec sheets. The selected values should be capable of generating the required quality but also at a productivity level that will ensure appropriate rates of throughput.

Concept 10. Enforce WPS parameters. Once a good WPS has been established, good productivity depends on welders following the WPS. Enforcement of compliance to WPS parameters should not be solely relegated to the welding inspector, or the AISC auditor, but should also be the responsibility of the supervisor that oversees the welding operations.

Today’s welding equipment can be programmed and locked to permit welders to only use specific parameters for a given weld or allow the welder to adjust the welding parameters only within acceptable ranges.

The proper application of this concept requires that welders have access to a WPS and know how to follow it. Welders should be trained to make quality welds with established WPS parameters. If welders cannot make quality welds with a given WPS, either the WPS needs to be adjusted or the welder needs further training.

Concept 11. For single-pass welds, think travel speed (not deposition rate). Welding deposition rates are measured in units of pounds per hour, while welding travel speeds are expressed in units of inches per minute (ipm). For single-pass welds, the best metric for evaluating productivity is travel speed. An all-too-common error occurs when deposition rates are maximized, but travel speeds are not proportionately increased.

Assume a ¼-in. fillet weld is required, as shown in Figure 12. Using a 0.045-in.-diameter FCAW-G electrode, the weld in Part a was made with a wire feed speed of 400 ipm and a deposition rate of 9.1 lb per hour. Using the same electrode, the weld in Part b was made with a wire feed speed of 520 ipm and a deposition rate of 12 lb per hour, which is 32% higher. However, the travel speeds for both of the welds were 13.5 ipm. Why did productivity not increase?

As is apparent from the weld cross sections shown in Parts c and d, the higher deposition rate simply resulted in over welding. No productivity gains were achieved and more weld metal than needed was deposited. This error occurs when undue emphasis is placed on deposition rates instead of travel speeds when single-pass fillet welds are made. In this case, the contractor should increase the travel speed listed on the WPS to take advantage of the productivity gains. Alternately, if the weld cannot be made at the higher travel speed, then the wire feed speed listed on the WPS should be reduced; while no productivity gain is seen, the over welding can be controlled.

Concept 12. Investigate robotic welding technology. Welding equipment and filler metal manufacturers are constantly innovating, looking for ways to enhance weld quality, reduce welding costs, and increase welder safety. A major focus of the past ten years has been on automation and robotics. What was not possible a few years ago is now a reality, even for fabrication shops with small runs of identical subassemblies.

Steel fabrication shops have recently shown an interest in collaborative robots (“Cobots”), like the one illustrated in Figure 13 on page 38. A Cobot is a robotic welding system that is designed for interaction with a human operator. It is a smart tool that bridges the gap between manual operation and full automation. Cobots can be easily programmed and are a safe, mobile, flexible option that can increase productivity, quality, and safety. They are particularly useful for repetitive welds and welds that require an extra level of quality and safety. Cobots are being considered as a part of the solution to the projected welder labor shortage. (See the articles “Robotic Revelations” in the January 2019 issue and “Robot Ready” in the January 2020 issue, both in the Archives section at www.modernsteel.com, for some perspective from fabrication robot manufacturers and steel fabricators considering or using robots.)

Again, the goal of AISC’s N4S initiative is to increase the delivery speed of a constructed steel project by 50%. Some of the increases will come from innovative breakthroughs, while other increases will come from the collective effects of smaller changes.

These smaller changes, such as the 24 welding-related concepts described in this article and its follow-up, are practical and can be implemented today. Innovative welding equipment and consumable manufacturers and their welding distributor partners are willing to assist forward-thinking steel fabricators and erectors in making these concepts into realities. While N4S may not be your primary focus right now, producing quality welds at a low cost and in a safe way will always be a challenge— and implementing even a handful of these concepts will materially improve welding operations for most fabricators and erectors. Stay tuned for Part Two of “Accelerated Welding” in the July issue.

AISC’s Need for Speed initiative recognizes technologies and practices that make steel projects come together faster. Check out aisc.org/needforspeed for more.