I will reply to some of this.... Qualifying welders and qualifying procedures  have different essential variables that need to be adhered to. When you are qualifying your welders, base metal group and wire diameter are not limited by the qualification.

For my prequalified WPS's, I list different wire sizes and their corresponding parameters in a chart on the bottom of the procedures. I generally have one procedure per joint detail, but I believe you can have multiple joint details on one WPS.

That's my 2 cents

I'm gonna hit this from another direction with a couple of questions that will follow some statements.

Any D1.1 base metal and joint configuration from 1/8" to unlimited thickness can be welded in all positions with a single diameter of FCAW electrode (.045 or 1/16")   Why complicate you life with multiple diameters?

Any D1.1 GMAW (Spray) base metal and joint configuration from 1/8" to unlimited thickness can be welded in the flat and horizontal positions with a single solid wire diameter.  (.045 or .052)  Why complicate your life with multiple diameters?

This will streamline your WPS's, quality manual, audits and purchasing.  It also will allow you to make WPS's with more efficient/productive parameters so that every weld leaving the shop looks the same (signature weld) which will please your customers and 3rd party inspectors..

Just a thought.

By no means an expert but would like to throw something out there for clarification. And forgive me if you were already aware of this.

1) A welder or Operator does not "Qualify" to use a WPS. He/She qualifies to weld within a range of variables designated for the production weld he/she is making.  A person could test on 3/8" thick material, be qualified to weld on material up to 3/4" and use a WPS in production that is qualified up to 2 inches. However because he/she is using that WPS, that does not mean he/she is qualifed to weld on 2" thick material.

2) WPS's are used a couple of ways
   a) To provide QC types with verification of an adequate paper trail that is code compliant for the project. Put all you can on one to cover all of the ranges possible and make sure you meet the code.
   b) To provide welders with clear and useful information related to the weld they are making that complies with the allowable range for the specific code. Place the information on the WPS in a manner that provides clear guidelines for usable paramters that are specific to the joint or joints including position.  Example, a prequalified WPS using 3/16" diameter E7018 on 5/16" butt joint in the vertical position, may very well "meet the code" however unless there is some serious "Welding magic" going on, its just wasted ink on paper.

Just my thoughts.

In my limited experience, most organizations are looking to create documents that fall more into a than b

Have a great day

Gerald Austin

One thing to sort out: WPS and Welder Qualifications have different essential variables as someone has already mentioned

There are two different tables, Table 4.5 for WPS essential variables, and Table 4.12 for Welder Qualification essential variables.

Essential variables are things that must be kept within these tables or requalification must take place.

It's easy to confuse these, but we have to keep them separate.

As they others have stated previously, if a welder qualifies with a single diameter, they are qualified to weld with any diameter-Table 4.12

Prequalified WPSs may have several diameters listed on a single WPS, but as you have stated, the parameters will be slightly different for each diameter. As Lawrence has pointed out, it simplifies things when you limit the use of a wide range of diameters in the shop down to one or two. I worked in a shop that welded a wide range of thickness and I limited it to two diameters. 1/16" and 3/32" FCAW wires...the 1/16" covered the thinner materials without burning through and the 3/32" was able to deposit a lot of material quickly to fill bevels for full penetration welds on 6" thick material.

FCAW and GMAW will have separate WPSs, each groove configuration should have different WPSs. You want your WPSs to be a useful tool for your welder, not just a piece of paper to pull out and dust off during a shop audit. I developed a welder's manual with all of the WPSs and fabrication notes required for them to do their job and feel comfortable while being quizzed by auditors. It really helped them find the joint in question quickly by placing the joint designation down by the page number so they could quickly thumb through and find the designation shown on the shop drawing in the weld symbol's tail. (ie. TC-U4b) 

Educating the welders to read and understand these welding documents goes along ways to increased quality and production in a fab shop.