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The Fluid Systems Engineering and Management Blog

by Swagelok Northern California

Good Orbital Welding Still Relies On Human Choices

by Jeff Hopkins, on 10/9/18 9:00 AM

A machine can perform only as well as the weld parameters set by the operator


"While a computerized orbital welder creates better, more consistent welds than a pair of human hands, the machine still needs a human to tell it what to do."

- From "Good Orbital Welding Still Relies on Human Choices"


While a computerized orbital welder creates better, more consistent welds than a pair of human hands, the machine still needs a human to tell it what to do. You have to choose the right electrode grind angle, arc gap, purge gas and other parameters. You also have to check the welder periodically as conditions change, to make sure it's still performing the way you want it to.

Tungsten electrodes

The electrode plays a major part in orbital welding. An orbital welding machine uses standard programs, and it can't make visual adjustment to differences in the grind of the tungsten. So here are a few things to consider when choosing an electrode and grind:

  •  Electrode grind angle is a trade-off. Shallow angles have more stability, but steeper angles give more penetration. The penetration factor is not as noticeable at current levels below 100 amps, where most orbital welding is done.
  •  Electrode tip diameter is another trade off. A small diameter gives ease of arc start, while a large diameter offers more power capabilities, penetration, and tungsten life. The diameter is a matter of choice, but it must remain constant between tungsten electrodes used on the same programs.
  • Electrode material is again a matter of choice, but three types are the most common. Thoriated tungsten has been used by hand GTAW welders for years but is not the oxide of choice for orbital welding because it is slightly radioactive, has poor restart capabilities, and short service life. Ceriated tungsten is a good choice. Lanthanated tungsten is less available in the United States, but is an acceptable choice.
  •  Electrode size is a function of the current required for the weld and the orbital weld head requirements.

 

 

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Arc gap

A narrow arc gap gives you better penetration, heat input, ease of arc start, and stability of the arc. But to a large degree, the gap is controlled by the weld current and the roundness of the tubing. When the roundness of the tubing changes, the arc gap changes. That, in turn, causes the heat input to change. So choosing an arc gap is a compromise between the optimal narrow gap and how well your material dimensions are controlled.

Purge Gas

Orbital welding jobs most often succeed or fail because of purge procedures. Gas purity is important. Standard grade argon, for example is 99.95 percent pure, while research grade is 99.99999 percent pure. Then there's electronic grade, which has additional requirements such as lower oxygen and moisture content.

Normally, inside-diameter purge gases must meet or exceed the installed system gas purity. Head purge gases, on the other hand, usually are not considered as critical.

It's possible to use cheaper ID purge gases, mainly nitrogen, on larger size tubing but not in all materials. N2 is not as inert a contaminant in many systems as argon.

The ID pressure must be controlled at the weld point and can be affected by number of factors such as the length of the tubing, number of fittings or bends, amount of elevation change and any connected components such as valves or regulators.


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Checkup

Here are some times when you should verify the weld parameters:

  • At the start and end of each shift.
  • When the ambient temperature changes by more than 20 degrees.
  • When you change any of the equipment, such as the weld head, weld head extensions or power supply (even adding or taking away an extension cord).
  • When there's a change in the tube size or wall thickness.


If some of that seems unfamiliar or overwhelming, don't worry. We can teach you what you need to know through our Swagelok Orbital Welding Training Course. You can get the details by calling us at 510-933-6200 or through our website.


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