10 Questions You Should to Know about Pipe Welding Turning Rolls

A tight grasp of most common mistakes in pipe welding process and how to avoid them will benefit tremendously your process of new welder training, raising quality and productivity and improving safety.

Whether it is about welding pipes for oil and gas industries or food and beverage, there are common problems that those in pipe welding positions overseas or locally should know about and find best ways to avoid. Those problems include everything from selecting a Mig gun with too low amperage to inappropriate drive rolls and shielding gas.  Because companies have been earnestly training new welders, working with new materials, raising quality and productivity, and improving safety, it is significant to center on some of those issues in pipe welding process that may affect those efforts. Given below are 13 most common mistakes made in pipe welding and how to avoid them.

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1. Forget to grind the joint after plasma or oxy-fuel cutting

Both plasma and oxy-fuel cutting processes add an oxide layer to the cut edge. This layer must be got rid of before welding because the oxide, commonly, has higher melting point than the base metal. The arc being hot enough to melt the oxide is synonym to that it&#;s too hot for base metal and can induce burn-through. Also, the oxides can remain in the weld, and lead to porosity, lack of fusion, inclusion and other defects of welding. Importantly, welders remember to grind the joint down to parent material before welding, and grind inside out diameters of the pipe to get rid of those oxides as well as other potential contaminants.

2. Make poor cut that induces poor fit-up and necessary gaps

When welders work on materials more subject to distortion and influences of higher heat input &#; for example, aluminum, stainless steel, a poor cut can be conductive to poor fit-up and produce unnecessary gaps. Then to fill it, welders compensate by placing more filler metal (hence, heat) into the joint. That added heat can induce distortion, and with such corrosion resistant pipes as stainless steel, can worsen the corrosion-resistance of the base metal. Also, it can result in incomplete or excessive penetration. Not all, poor preparation induces longer weld cycle times, potential repairs and higher consumable costs.
Currently, shops employing band saws or chop saws to cut pipe should consider purchasing specialized orbital pipe cutting equipment to ensure cuts within thousandths of an inch of specified parameters. That precision would help guarantee best fit-up and minimize the amount of filler and heat into the joint.

3. Forget to cut out and feather tacks

Tacking is crucial to fit-up, and welders are recommended to cut out and feather tacks to ensure consistency of the final weld. Specially, in shops that a fitter gears up for the pipe and somebody else welds it, it is important that the welder knows what is in the weld. The tack left in the joint would be consumed by the weld. If there is a tack defect, or if the fitter employed the incorrect filler metal to tack the joint, there may induce defects in the weld. To avoid this potential problem, cut out and feather the tacks.

4. Prepare a joint for Mig welding processes in the same way as for stick welding

Welding training is a top priority in many shops. Not few welders apply past experiences to the new job. Those experiences can be dealt with adequate training though, one common mistake is that welders with stick experience don&#;t understand how to appropriately prepare a joint for the wire processes in pipe welding applications. Often, those trained in stick and Tig welding prepare the joint with the heavy landing area and desire to keep the gap narrowest as possible. Because shops now turn to such easier and more productive Mig processes as Regulated Metal Deposition, they prefer that welders take down the landing area to an edge of knife and space the joint at about 1/8 inch. This area is wider than that that those trained in stick and Tig processes use, and can induce various problems &#; for instance, incomplete penetration, too much heat into the weld edges, not enough reinforcement on inside of the pipe. Then shops should train their welders about particulars of each application and ensure they understand weld preparation and operational techniques before they come to work.

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5. Mistakenly believe that more shielding gas is always better

A misconception among some welders is that more shielding gas is better. They crank gas wide open, and mistake that they are giving more protection to the weld. That technique results in lots of problems like wasted shielding gas in terms of cost and resources, increased agitation of weld puddle, convection effect sucking oxygen into the weld and inducing to porosity. Each station should be equipped with a flow meter, and each welder should seize how to set and follow the recommended flow rates.

6. Count on mixing with the flow regulator

There are shops that build a separate tank of helium and a separate tank of argon for the stainless steel application that needs 75/25% of argon/ helium. Then they count on the flow regulator to bleed in the right amount of shielding gas. In fact, with this method, you won&#;t know what you get in a mix. Buying mixed gas from trusted sources, or buying an appropriate mixer will ensure you exactly know what you are shielding your weld with and you are following proper weld qualifications/ procedures.

7. Think welding power sources cause porosity

Some welders blame welding power sources for porosity in welding. Indeed, they are not the culprit of this problem. If welders track back their steps from the point that porosity began, they will often find that this problem began when a wire spool was changed, a new gas cylinder was used (loose connections, wrong gas used), when someone failed to prepare properly the materials (oxides appears in the weld), or if the material suffered contamination from somewhere else along the line. Most often, the problem results from an interruption, or trouble with the gas flow. Looking back their steps, welders will often realize the variable causing the porosity.

 8. Use wrong type or size of drive roll

While flux cored wires should be employed with the knurled drive roll, a standard V drive roll should be used for solid wires. Critically, welders remember to change those out when changing types of wires in their machines. Welders that wrongly use the standard V drive roll with the flux cored wire will often notice this wire slipping, crank down on the tension of drive roll to hold it in place, thereby crushing the cored wire. When incorrectly using the knurled drive roll with solid wire, welders will notice the roll chip off the outer coating on the wire, and that induce plugging up the liner. Then welders tend to crank on the tension; that just worsens the problems.

If welders find themselves having to crank on the wire tension, it indicates something else wrong with the process &#; incorrect drive roll, incorrect drive roll size, clogging in the liner. Work the process, ensure using the right drive rolls, and they will likely find the cause of the problem.

 9. Add cleaning solvent or lubricant to the dust pad

Some shops add the dust pad (i.e. a small piece of fabric) just before the drive roll system to get rid of any final contaminants from the wire. This is fine on its own, but some shops have been seen to add cleaning solvent or lubricant to the pad to further enhance feeding or clean the wire. That turns out to have the opposite effect &#; those oil, indeed, contaminate the wire, and can induce weld defects. For added protection or as an alternative, welders can also add a spool cover to save the spool of wire from the airborne contaminants.

10. Use wrong nozzle size

There require different types and sizes of nozzles for different Mig processes. For example, a tapered nozzle is recommended for the regulated metal deposition process. Still, that same tapered nozzle can&#;t address the gas flow requirements of pulsed Mig process, and will induce inappropriate gas coverage of the weld. Seize which nozzles is suited for each process/ variable, and use accordingly.

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11. Fail to select a Mig gun rated for handling peak amperage when pulsing, and mixed gases as well

When shops specify a Mig gun for the pipe applications, they will often choose a Mig gun by the average amperage of their application. They may purchase a Mig gun of 250 amperage, and have 250 amps as the average amperage. But they are applying substantially higher amperage to that gun during the peak of pulsing cycle. Those guns aren&#;t designed for that peak amperage and then can burn out more quickly. 

Likewise, Mig guns are often rated for use with 100% CO2. That is fine for the applications welding with 100% CO2 though, that available amperage on that gun reduces once the mixed gas common in pipe welding applications is applied.

Many shops find for low amperage guns as they are lighter and less costly, but that isn&#;t good in the long run. They should select the Mig gun rated for dealing with peak amperage when pulsing, and mixed gases as well.

12. Jump into mechanized/ automated processes without seizing why

One common mistake is the desire to apply mechanized or highly automated robotic process without doing the homework. The automated welding processes can just as effective as upstream and downstream processes in a shop. The automated cell isn&#;t helpful when sitting idle because upstream processes are still slow, or when creating new bottlenecks downstream.

There are 2 important things that a shop must do first &#; Seize the issue they are trying to handle through automation, and them make everything else in the operation simple to make sure of the appropriate workflow as well as optimal efficiency at each station. 

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13. Rely on smaller, less expensive machines

There are shops that use 250-amp shop welders and believe they will give the needed power and performance to carry out any pipe welding applications. They may be right, in some cases.

Still, those smaller, less costly machines would feature lower duty cycles, fewer capabilities. If your shop takes pipe fabrication seriously, and desires to maintain high levels of productivity, operating at the higher duty cycles will guarantee consistent use. It&#;s far from similar between 250 amperage at 20% duty cycles (2 mins on out of a 10-min cycle) and 250 amperage at 100% duty cycle (10 mins of continuous welding in a 10-min cycle).

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