Circling the Issues
Industry experts weigh in on troubleshooting common challenges in pipe welding
Whether it’s out in the field or in the fabrication shop, pipe welding processes and techniques require an exceptionally skilled welder. Not only is it a physically taxing job, there are many variables to consider that will have detrimental effects on weld quality and productivity, such as wire feed speeds, filler metals, proper fit up, amperage, shielding gas choice and flow. And that’s before you the arc length settings for the welding process being used, such as stick, MIG, TIG or flux-cored.
Working through all of those variables can be complicated and daunting. But according to Jeff Robedeaux, technical product specialist for Miller Electric Mfg., one of the biggest issues in the pipe welding world is much less complex: simply not using the right nozzle and tip configurations.
“We would recommend using a smaller tapered nozzle to focus the gas on the root pass, and then a larger one to get more gas coverage with a flux-core process,” he says. “Sometimes welders will try to use the tapered one for flux-core and not get the proper gas coverage, which will cause porosity or melt the nozzle. If they have the wrong size of tip, such as a 4/5 nozzle tip and they run 3/5 wire, that wire could come out like a corkscrew, which can be difficult to weld.”
Bill Hall, key account manager, Abicor Binzel, agrees. “Depending on joint configuration, the nozzle size and style are very important. Typically, when welding by hand, the welder likes to use a tapered nozzle and contact tip to have good access to the root opening to assure a sound root pass. As they fill the pipe joint with the ensuing passes, they may stop and change the nozzle to a larger opening to give better gas coverage.”
Hall says welders should avoid the temptation to keep going with the smaller nozzle to save time. “This is not recommended, as they will get spatter accumulation and potential porosity issues.”
Bridging the Gap
Robedeaux says getting proper weld penetration is a common struggle for many welders. About every two weeks, his team will get a call from a shop struggling with proper penetration on a weld.
“A lot of that comes down to the fit up of the pipe or a tight root gap,” says Robedeaux. “Improper fit up can be a common problem. Before Miller, I was a pipe welder and I can’t believe the things I’ve seen over the past 15 years with improper fit up.”
He says some of the more common problems involve an improper bevel on the pipe, or no bevel at all on thicker pipe, or too much of a land on the bevel.
“One thing that we see a lot of is the root gap not being big enough. If it’s too tight the welder can’t get penetration. At the end of the day, you have to make sure you have the right bevel, proper land and the correct gap,” he says.
When it comes to proper fit ups, one of the biggest problems is with pipe that’s not exactly round. Trying to fit two pipes together that don’t fit perfectly, the welder often tries to get it as close as possible and manage the gaps and fittings where they match up.
There are a number of ways to cut the pipe, and all have advantages and disadvantages. Regardless of how the pipe is cut, the edge should have a consistent bevel and a land, a feathered edge or other prep as specified. The more inconsistent the prep and fit up, the more difficult it is to create a sound weld joint. “Pipe welding takes a higher skill level than many other types of welding, and combined with the shortage of skilled welders, there is an obvious need to simplify it. This is where the collaborative welding robot from Novarc Technology fills the gap,” says Hall.
Abicor Binzel offers the Novarc Spool Welding Robot (SWR), a collaborative welding robot that replicates the welder’s hand and arm in the 1G position during the pipe welding process.
“The robot still needs a welder who understands the welding process to make minor adjustments to changes in fit up from joint to joint,” says Hall, who says the SWR will help an average welder increase his productivity immediately. With the SWR, a worker can now weld the pipe from root to cap without stopping to change the nozzle, grind their stops or clean the weld.
The SWR allows the welder to observe the weld on a monitor—in greater detail than by hood alone—and make adjustments on the fly, giving the welder control while ensuring consistent weld quality.
Like all welding processes, preparing the material to be welded is paramount. Any kind of oxide layer or lubricant from a cutting process can cause porosity if not properly ground down and cleaned.
“Prepping the material is important in every aspect of welding. Whether it’s automated, semi-automated, robotic, or manually welded, proper prep is key,” says Hall. “You have be sure to get contaminants out, you want your fit up to be as good as possible and your tacks done correctly to accomplish x-ray quality welds.”
Robedeaux agrees, adding that most shops do a pretty good job of it when using common materials. With stainless steel, shops are good at cleaning it and creating the proper bevel. It’s the thinner metals like Schedule 10 that are more difficult to fit up. “Sometimes they don’t have the proper clamps or the stainless pipe is egg shaped and they don’t have the proper root in,” he says.
“If you’re talking about food grade stainless prepping and welding, that is a totally different animal because a product is going to go through it. You can’t have penetration on the inside as bacteria will grow in the pipes,” continues Robedeaux. “A lot of that kind of process is done with mechanized systems such as orbital welding, where they clamp onto the pipe and move around it with TIG welding.”
High heat is also an issue for stainless. If you apply too much heat, it can distort the pipe and ruin the chemical properties, which could cause rust.
With the Novarc SWR, the welder can control the heat input for metals that require control of interpass temperatures by stopping and starting to maintain the specified interpass temperatures. Once your pipe gets to its maximum allowable interpass temperature, the welder simply stops the machine and waits for the material to cool down. They would then restart without modifying the program, which is the downside of some other fully automated equipment.
The Spool Welding Robot allows the welder to make changes as necessary, such as adding or decreasing wire feed speed, voltage, arc length, arc control or positioner speed while welding.
At FabTech 2019 in Chicago, Novarc introduced NovEye, an AI camera that monitors all the weld data, as well as the gap and fit up, to help make adjustments quickly and accurately. All of this data, including changes, are recorded in a report for every weld. NovEye also adjusts for welding over tacks and makes adjustments for wider or narrower gaps.
Dialing in Gas Flow
Many have been taught that more shielding gas is better. That is, in fact not the case, and can cause porosity in the weld. “If you don’t have enough gas, you’re obviously not covering the puddle,” says Robedeaux. “The gas mix you use is a big thing, especially with stainless. If you have gas that has too much CO2 in it, there may be rust issues. With carbon steel, you have to have a minimum argon percentage. If you use less argon, you’re going to get a lot of spatter. So gas mixture is critical.”
In terms of flow rate, if you’re welding a short circuit transfer at a colder temperature, you won’t need as much gas. But when you get up to hot spray or pulse welding, a lot more gas is needed.
“Welders, when setting their gas flow, have to settle on enough flow for the highest amperage application to assure good gas coverage. Unfortunately this wastes a lot of gas,” says Hall. “The Novarc SWR has the Binzel EWR (electronic weld regulator) that monitors the current flow and adjusts the gas flow to match. By using the EWR, savings of 40 per cent or higher can be realized.”
Honing in on such common pitfalls of pipe welding will not only save shops time and money by prepping the materials and setting the perfect pass, but also save on consumables and increase productivity.
As the world moves towards more automation, collaborative welding systems have filled a niche, as they are more ergonomic for the welders and help maintain critical consistencies in the processes. One must also consider the lack of highly skilled welders and how a collaborative system, while it still requires a knowledgeable eye on the arc, could allow shops to bring in less skilled workers. SMT