148 Base Metals

In this category there are no nonessential variables. There are only essential and supplementary essential variables. Supplementary essential variables apply only when impact properties are required (which are not on the exam). This put restrictions on the base metal material that can be qualified with any one PQR. It also puts restrictions on the base metal thickness range that can be qualified when running a PQR. Group Number: A change in a group number becomes an essential variable when impact properties are required of the base material (since this is a supplementary variable it need not be addressed on the exam). T Limits Impact: In QW-403.6 the minimum thickness ranges qualified by impact testing is called out (again a supplementary variable not on the exam).

T/t Limits > 8 in.: This is the first essential variable in the base metal category. It becomes effective when trying to qualify welds greater than 8 inches in thickness (has never been an issue on the exam).

Change in T Qualified: Essentially it stipulates that the welding procedure depending on the thickness of the coupon used in the PQR is qualified for a range of base metal thickness. If base metal thickness goes beyond that qualified, a new PQR will be required.

t Pass > 1/2 in.: This variable speaks to weld passes that deposit a single pass weld metal layer greater than ½” inch in thickness. When weld metal is deposited in a thickness greater than ½” within a single pass, the WPS has a different qualified thickness range than one made with passes less than ½”. A thickness pass greater than ½” limits the base metal qualified to 1.1x T, where T is the thickness of the PQR test coupon. As you will later see in QW-451.1 most procedures will have a maximum thickness range qualified of 2 times the Test Coupon (T) for example 2 x T. Therefore a ½” coupon would yield a maximum thickness of 1” under normal circumstances.

Change in P-No.: Any change in P-Numbers requires re-qualification of the procedure.

Change in P-No 9/10: Here we find changing from P-No. 9A to P-No. 9B is considered a change but not the reverse. For the P-Nos. 5A, 5B, 5C and P-Nos. 10A, 10B, 10C a change from one to the other is essential and would require re-qualification by the welding of a new PQR coupon and testing it.

Filler Metals

In the filler metal category, all three types of variables apply. The first two have to do with chemistry and the types of electrodes used in the welding process. The F Number is a grouping of electrodes that have similar characteristics in the way that they produce mechanical properties. Deposition is also similar among f-numbers. A-Numbers define chemical limitations and all electrodes that fall under the same A-Number have similar chemical properties. A-Number applies only to ferrous materials.

Change in F-number: Requires re-qualification of the procedure.

Change in A-Number: Requires re-qualification of the procedure, except as given in QW-404.5, which says that A-No. 1 and A-No. 2 can be exchanged. How the A number is determined is detailed in QW- 404.5

Change in Diameter: Since this is a nonessential variable changing it does not demand re-qualification of the procedure. However, you should revise the WPS to reflect the change.

Change in Diameter > 1/4 in.: This is listed as a supplementary essential variable. It says that if impact properties are necessary and an electrode of greater than 1/4 inch is used, that size electrode must be qualified for impact properties in the weld (once again not on the test).

Change in AWS Class: Requires re-qualification as a supplementary variable if impact properties are required. This is an SFA number given in Section II of the ASME Code.

Change in t: A change in the thickness of deposited weld metal beyond the range qualified. This comes into play when more than one class of filler metal is used during the PQR coupon welding.

150 Position

There are three variables listed for position. Notice that unless impact properties are required position is a nonessential variable.

Addition of a Position: Nonessential but the WPS must be revised if one position is given then another is used in production.

Change in Position: A supplementary essential variable (not on the test), which becomes essential when impact properties are required. Specifically when you change from any position to vertical uphill progression. Also if changing from a stringer bead in the vertical uphill to a weave bead. Either will require re-qualification of the procedure.

Preheat

There is one essential variable, one supplementary essential, and one nonessential variable listed in this category.

Decrease > 100 degrees: If a procedure is qualified at a given preheat, a reduction of that preheat by greater than 100 degrees in production requires re-qualification of the WPS. If the PQR used 350 oF WPS will use 249 oF re-qualification would be required.

Preheat Maintenance: This is the continuance of preheat temperature after the completion of welding. Will preheat be maintained for a given time or will the weld be allowed to cool in air and not monitored? Increase > 100 degrees:(interpass temp): If the weld requires impact values using the Shielded Metal Arc process, the interpass temperature must be maintained below some maximum temperature. If the interpass temperature is increased by more than 100 degrees over what was qualified, the procedure must be re- qualified.

Post Weld Heat Treatment

The first variable given is a change in postweld heat treatment. This is an essential variable. While it is not always necessary to postweld heat treat a material, a change in postweld heat treatment or the lack of is an essential variable and must be reflected on the WPS and the PQR.

Change in PWHT: If PWHT will not be performed, this should be indicated on the WPS by entering the words: "No Postweld Heat Treatment" or simply "None". If PWHT is required and then changed from that specified on the WPS, the WPS must be re-qualified since it is an essential variable. The WPS and PQR must be in agreement on PWHT.

PWHT (Time and Temperature Range): Again when impact properties are required of a weldment, a change in the time span of PWHT or the temperature range will require re-qualification of the procedure. Thickness Limits: As indicated, this is an essential variable. It deals with exceeding the upper transformation temperature of alloys. It states that if the test coupon being heat treated exceeds the upper transformation temperature of the alloy the maximum thickness qualified is 1.1 times the thickness of the test coupon as opposed to two times the coupon thickness allowed if the upper transformation has not been exceeded. See QW-451 for T limits.

Electrical Characteristics

Change in Current or > Heat input: This is a supplementary essential variable that deals with impact properties. Here if the heat input due to welding is changed or the type of current is changed resulting in an increased deposition of weld metal the procedure must be re-qualified for impact values (you guessed it, not on the exam).

Change in the Type of Current or a Change in the Current or Voltage Range: These are both nonessential, but if changed in the WPS must be revised to reflect the change.

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