Avoid These 13 Common Pitfalls in Process Pipe Welding Applications
There are many variables that go into making the perfect weld on a section of pipe. Here are some common mistakes welders make and how you can avoid them.
We get a lot of questions about welding pipe. Whether it’s about welding high-pressure pipe, high purity pipe for food and beverage industries, or pipe for the oil and gas industries, there are a number of common elements we see in pipe welding and fabrication that lead to problems. These include everything from improper shielding gas and drive rolls to choosing a MIG gun with too low of an amperage rating. As companies push to train new welders, work with new materials, increase quality and productivity, and improve safety, it is important to focus on some of these basic variables in the pipe welding process that can affect these efforts. In this article, we’ll look at 13 of the most common issues we see in pipe welding applications and how to resolve them.
1. Forgetting to grind the joint after oxyfuel or plasma cutting
Both the oxyfuel and plasma cutting processes add a layer of oxide to the cut edge. This oxide layer must be removed prior to welding, as the oxide often has a higher melting point than the base metal. Once the arc gets hot enough to melt the oxide, it’s too hot for the base metal and can lead to burnthrough. The oxides can also remain in the weld and cause porosity, inclusions, lack of fusion and other defects. It is important that welders remember to grind the joint down to the parent material prior to welding, as well as grind the inside and outside diameters of the pipe to remove these oxides and other potential contaminants.
2. Cutting corners with cutting
When welders work with materials more prone to distortion and the affects of higher heat input, such as stainless steel and aluminum, a poor cut can lead to poor fit-up and create unnecessary gaps. Welders then compensate by putting more filler metal (thus, heat) into the joint to fill it. This added heat can lead to distortion and, with corrosion-resistant pipe like stainless steel, can reduce the corrosion-resistant qualities of the base metal. It can also lead to lack of penetration or excessive penetration. Poor preparation also leads to longer weld cycle times, higher consumable costs and potential repairs.
Shops currently using chop saws or band saws to cut pipe used in critical process piping applications should consider buying dedicated orbital pipe cutting equipment to guarantee cuts within mere thousandths of an inch of the specified parameters. This precision helps ensure optimum fit-up and keeps the amount of filler and heat put into the joint at a minimum.
3. Forgetting to cut out and feather tacks
Tacking is critical to fit-up, and best practices recommend that the welder cut out and feather that tack to ensure the consistency of the final weld. Especially in shops where a fitter prepares the pipe and then someone else welds it, it’s important that the welder knows just what is in the weld. Tacks left in the joint become consumed by the weld. If there is a defect in the tack, or if the fitter used the wrong filler metal to tack the joint, there is a risk for defects in the weld. Cutting out and feathering the tacks helps eliminate this potential problem.
4. Preparing a joint for MIG processes is different than with Stick welding
Training welders is a top priority for many fab shops, and — for better or worse — many welders bring past experiences with them to the new job. These experiences can be addressed with adequate training, but one common mistake we see is welders with Stick experience not understanding how to properly prepare a joint for wire processes common in pipe fabrication applications. Welders trained traditionally in Stick and TIG welding often prepare the joint with a heavy landing area and want to keep the gap as narrow as possible. As pipe shops switch over to easier, more productive MIG processes such as Regulated Metal Deposition (RMD™), we prefer welders take that landing area down to a knife’s edge and space the joint at approximately 1/8-inch. This area is wider than those trained in Stick and TIG processes are used to and can lead to a number of problems: focusing too much heat into the edges of the weld, a lack of penetration and insufficient reinforcement on the inside of the pipe. Shops should train their welders to the specifics of each application and make sure they understand different weld preparation and operational techniques before they go to work.
5. More shielding gas is not always better
Some welders have a misconception that “more shielding gas is better” and will crank the gas wide open, mistakenly believing they are providing more protection to the weld. This technique causes a number of problems: wasted shielding gas (resources and cost), increased and unnecessary agitation of the weld puddle, and a convection effect that sucks oxygen into the weld and can lead to porosity. Each station should be outfitted with a flow meter and each welder should understand how to set and adhere to the recommended flow rates.
6. Buy mixed gas – don’t rely on mixing with flow regulators
We have seen shops that, for a stainless steel application that requires 75/25 percent argon/helium, set up a separate tank of argon and a separate tank of helium and then rely on flow regulators to bleed in the proper amount of shielding gas. The truth is you really don’t know what you’re getting in a mix with this method. Buying cylinders of mixed gas from reliable sources, or buying a proper mixer, will ensure you know exactly what you’re shielding your weld with and that you’re adhering to proper weld procedures/qualifications.
7. Welding power sources don’t cause porosity
It is not uncommon to get a call from a customer who says “Hey, I’m getting porosity from your welder.” Plainly, welding power sources don’t cause porosity. We tell welders to recount their steps back from the point where the porosity began. Welders will often find that it began just when a gas cylinder was changed (loose connections, incorrect gas used), a new wire spool was put in, when someone didn’t prep the material properly (oxides present in the weld), or if the material was contaminated somewhere else along the line. Most of the time the problem is caused by an interruption or problem with the gas flow. Tracing back your steps will often lead to the variable that caused the porosity.
8. Incorrect type or size of drive roll
Flux-cored wires should be used with a knurled drive roll while solid wires should be used with a standard V drive roll. It is critical that welders remember to change these out as they change types of wires in their machine. Welders who incorrectly use a standard V drive roll with flux-cored wire will typically notice the wire slipping and then crank down on the drive roll tension to hold it in place, which then crushes the cored wire. Knurled drive rolls will chip off the outer coating on solid wires and that leads to plugging up the liner. Welders then tend to crank on the tension and the problems gets worse.
Bottom line: if you find yourself having to crank on the wire tension, it is a symptom of something else wrong with the process: wrong drive roll, wrong drive roll size or clogging in the liner. Work the process, ensure you’re using the right drive rolls, and you’ll likely find the cause of your problem.
9. Do not add cleaning solvent or lubrication to your dust pad
Some shops will add a dust pad — a small piece of fabric — just prior to the drive roll system in an effort to remove any final contaminants from the wire. This, on its own, is fine, but we’ve seen some shops add a lubricant or cleaning solvent to this pad in an effort to further improve feeding or “clean” the wire. It has the opposite effect: these oils actually contaminate the wire and can lead to weld defects. As an alternative or for added protection, you could also add a spool cover to protect the spool of wire from airborne contaminants.
10. Incorrect nozzle size can cause problems
Different sizes and types of nozzles are required with different MIG processes. For instance, we recommend a tapered nozzle with the RMD process available on our PipeWorx welding system. That same tapered nozzle, however, cannot accommodate the gas flow requirements of the Pulsed MIG process and will lead to improper gas coverage of the weld. Know which nozzles match up with each process/variable and use accordingly.
11. Choose a MIG gun rated to handle peak amperage when pulsing, as well as mixed gases
When specifying a MIG gun for pipe applications, shops will often select a MIG gun based on the average amperage of their application. They may buy a 250-amp MIG gun and have an average amperage of 250 amps, but they are subjecting that gun to considerably higher amperages during the peak of the pulsing cycle. These guns are not designed for that peak amperage and can burn out at a faster rate.
Similarly, most MIG guns are rated for use with 100-percent CO2. That’s fine for applications that weld with 100-percent CO2, but the available amperage on that gun decreases as soon as a mixed gas common in most pipe welding applications is used.
We understand that shops will lean towards low amperage guns because they are lighter and less expensive, but the hassle is not worth it in the long run. Our Pipeworx system comes with a gun rated at 300 amps to solve some of these problems. Always work towards the higher end of your welding needs.
12. Jumping into automated/mechanized processes without understanding “why?”
One common mistake we see is a desire to jump into highly automated robotic or mechanized processes before doing the proper homework. Automated welding processes can only be as effective as the upstream and downstream processes in a shop. An automated cell does no good if it’s sitting idle because upstream processes remain slow, or if it’s creating new bottlenecks downstream.
There are two critical things a shop must do first: understand fully the issue they are trying to solve through automation, and then simplify everything else in the operation to ensure the proper workflow and optimal efficiency at each station. We have often found that, in taking the time to examine the issue a shop is trying to solve, they discover other efficiencies upstream that solve their initial problem – saving them the time and expense of new infrastructure to automate the process. Or they may discover that a simple mechanized set-up may suffice instead of a more intensive robotic cell.
13. Buy a machine that can handle the work… and then some
Pipe welding is its own animal. We’ve seen shops that look at a 250-amp shop welder and believe that it will provide the power and performance needed to perform any number of pipe welding applications – and in some cases, they may be right.
Those smaller, less expensive machines also come with lower duty cycles and fewer capabilities. If your shop is serious about pipe fabrication, and wants to maintain high productivity levels, operating at higher duty cycles will ensure consistent use. It’s the difference between 250 amps at 20 percent duty cycle (2 minutes on out of a 10 minute cycle) versus 250 amps at 100 percent duty cycle (10 minutes of continuous welding in a 10-minute cycle).
The Pipeworx pipe welding system from Miller, for example, is rated at 400 amps at 100 percent duty cycle, ensuring a strong, consistent welding arc all day long without having to stop, in most process pipe scenarios, to let the machine rest. This robustness is particularly helpful in applications such as Flux-Cored welding in roll welding applications with larger diameter wires and higher wire feed speeds where the power source continually works at higher amperage levels.
These more robust industrial welding systems also offer strong multi-process capabilities – critical in pipe applications where you may be running a Stick or TIG root and then switching over to a wire process for the hot, fill or cap passes. They also offer new processes, such as RMD, that are easier for new welders to learn and become proficient at – critical as shops continue to hunt for skilled welders. Having these capabilities in one system helps reduce changeover time and costs, the hassles of using multiple pieces of equipment, and the downfall of operating equipment that needs to spend more time resting than working.
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