ARC MAGAZINE

A Path To Walk The Cup

Walking the cup is a welding technique often employed in the process and power piping industries (though it is appropriate for other applications) as a means to smoothly advance the torch around the pipe or tube while maintaining a consistent arc length. The technique involves resting the insulated ceramic nozzle, commonly referred to as the cup, against the workpiece and manipulating the torch as a way to advance it forward.

The cup-walking technique provides several benefits compared with the freehand technique, including reduced operator fatigue and better torch control. Safety is a factor as well. The pipe can get extremely hot, meaning fabricators cannot rest their hands on the material.

There are many different variables that determine the correct fit up and procedure to use when welding pipe. For example, when welding a 6G 6-inch Schedule 80 carbon steel pipe in the field, an engine-driven welder may be used with a valved torch. There are times when gas tungsten arc welding (GTAW) is specified to weld the entire joint, while other times just the root and hot pass are performed with GTAW followed by other more productive processes for the fill and cap passes.

The coupons are cleaned and prepared to a specified bevel and edge preparation. The pipes are fitted and tacked in four places with a gap just slightly less than 1/8 inch and placed in the 6G position.

The touch start method is typically used with a No. 26 torch, and the shielding gas is manually turned on and off with a valve on the torch.

One way to deposit the root pass is to use the lay wire technique with a No. 5 or No. 6 cup and 1/8-inch alloyed tungsten electrode. The electrode is extended beyond the cup far enough to allow the torch to lean back slightly while maintaining a close arc length.

For the lay wire technique, the filler wire, which is typically the same size as the root opening, is added at the front of the tack and left tightly in the joint as welding progresses through other tacks.

The cup rests on both bevels, also referred to as 2-point contact, and it’s manipulated slightly by rotating the wrist from side to side. The arc is started on the bevel and moved to the bottom tack. For the lay wire technique, the filler wire is added at the front of the tack and left tightly in the joint as welding progresses through other tacks to assure complete penetration.

The inside root pass profile should be no less than flat to slightly convex, and should not exceed 1/8-inch maximum reinforcement.

When welding, the arc should be started on the bevel and brought into the joint. When the weld is complete it should be brought back onto the bevel to prevent potential issues caused by the crater. This technique should also be used when tacking the pipe together to assures that no silicon island is left in the root pass. The crater and silicon island left on the bevel are re-melted during subsequent passes.

The hot and fill passes are typically put in with higher current and larger cup sizes to allow the 2-point contact with the bevel but without touching the cup on the previous weld. As the bevels are filled up, a larger cup and 1-point contact are often used by rolling the cup over the previous weld. Likewise, the 1-point rolling technique is used on thinner-walled pipe where there is no bevel.

Walking the cup is a common welding technique that smoothly and evenly advances the torch around a pipe or tube while maintaining a consistent arc length.