• Tube welding is often used to make custom motorcycle frames.motorcycle image by Bionic Media from Fotolia.com
  
  Welding provides a simple method for joining sections of pipe and tube. According to Pipe Welding Procedures, it's the most common method for joining pipe in the early 21st century. However, pipe welding can be significantly more difficult than welding flat metal sheets. The welder must move the gun forward at a consistent rate to maintain joint thickness and appearance. Pipe welding takes some practice and background knowledge, but is a very effective method for joining metal pipes and tubes.
  
  

Gas Mixture

• According to Miller, a major producer of welding supplies, most tube welding uses gas metal arc welding, or GMAW. This method involves surrounding the welding wire with an inert gas, often carbon dioxide. However, for tube welding, Miller recommends a mix of 75 percent argon and 25 percent carbon dioxide. This mix provides better control and less spatter. A mix of this type also reduces the chance of melting through thin tubes, since it requires a lower voltage and allows the welder to feed the wire at a slower rate than an all-CO2 shielding gas.
  
  

Layers

• When possible, tube welding should occur in a single pass. However, when a continuous weld cannot be made, the join should be created from multiple interlocked layers. According to Fundamentals of Professional Welding, there should be one layer for each 1/8 inch of tube thickness, and the layer should be deposited with a weaving motion. Once a layer cools, the welder should clean it thoroughly before laying down the next, to prevent debris from being trapped in the weld.
  
  

Alloy Pipe

• Pipes made from metals which have been highly alloyed may be more difficult to join than low-alloy metals. According to Welding Journal, alloys have a lower thermal conductivity than steel, resulting in a less-viscous weld pool. Welders joining sections of alloy tubing must work more slowly to avoid an incomplete weld. Helium gas may be added to the shielding mixture to increase penetration, and wire extension should be as short as possible. This helps ensure that the welding arc stays inside the envelope of shielding gas.
  
  

Cooling

• It may be necessary to allow the metal to cool between welds, or between layers of a weld. Working on excessively hot metal increases the chance of undesirable melting. When welding several tubes together, such as for a motorcycle frame, the welder may wish to skip around the frame, partially welding a joint and moving on to the next. This allows the first weld to cool completely and reduces the chances of melting thin tubes.