Welding standards or codes typically lists those variables that considered to be either an "essential" variable or "nonessential" variable. Most WPSs have to address both essential and nonessential variable. The procedure qualification record has to at least address the essential variables. The classification of a welding variable as essential or nonessential changes from one welding standard to another. Even the terms I used, i.e., essential and nonessential variables, may change from one standard to another.

You need to list those variables that apply to either the WPS and/or the PQR as dictated by the applicable welding standard. You may also decide to list the welding variables that are not required if they provide additional information to the welder. For instance; travel speed, it may be a nonessential variable or not required for some low carbon steels that will be subjected to static loads at room temperature. However, if the application involves dynamic loading at temperatures below the transition temperature, charpy impact testing may be required when qualifying the welding procedure. In that case travel speed will influence the cooling rate, heat input, and grain size. Those factors will influence the notch toughness of the weld and HAZ. Bottom line, travel speed becomes a varible that needs to be controlled. Please refer to B2.1-2005, paragraphs 2.14.8 and 2.14.9(11), these paragraphs indicate when "travel speed" must be addressed by the PQR, thus the WPS as well.

Another consideration maybe the maximum width of a weld bead if that is of concern. There is currently a post of weaves versus stringers that is an interesting read. If the width of a weld bead is a concern, it should be addressed in the WPS. One way to limit the width of the weave is to place limits on the travel speed. Again, travel speed may not be required, but it may be to your advantage to list reasonable ranges.

Hope this is helpful.

Best regards - Al