What is the Welding Procedure Qualification Record (PQR) & Welding Procedure Specification (WPS)?


Introduction to WPS & PQR

This article list out the requirements for procedure qualification record (PQR) based on BPVC ASME Code Section IX.

The main aim of qualifying a WPS is to show that welding process proposed for production welding has required mechanical property for the intended purpose. 

The WPS is written by a company-designated welding engineer as per ASME Section IX but needs to be tested to ensure the produced weld based on WPS has the required mechanical property. When the WPS provided, then a test sample shall be prepared and welded. All welding variables must be recorded during the welding. Please note in WPS you have the range, but you will not have a range in the PQR (As PQR list the actual welding variables, a range can be given for, e.g. welding current from low to high that happened during welding), and you need to record a single value for each specified variable.

Welding Procedure Qualification Records in ASME Code Section IX

The test specimen size and dimension must be based on identified values in ASME Code Section IX. After completion of welding and heat treatment (if needed), you need to send the test specimen to the metallurgical lab for mechanical testing. For any PQR, normally two tension tests, two root face bend test and two face bend test is required. 

The acceptance criteria have been provided in the ASME Code Section IX. The QW-451 table provides you the information about number and type of tests. For example, if your test specimen is greater than the ¾ inch you cannot perform root and face bend test and instead you need to run 4 side bend tests.

The acceptance criteria for tension test have been provided in QW-153.1. The test specimen should not be broken below the minimum specified tensile strength of base metal, but if it breaks in out of weld area or out of weld interface then would be acceptable if it is not more than 5% below the minimum specified tensile strength.  For instance, if you material is SA 516 Gr 70, and it breaks out of weld area on 67 ksi then the test would be acceptable.  

The acceptance criteria for bend test have been provided in QW- 163. Normally after bend test there should be any crack more than 1/8 inch on the side that was placed on the stress. 

The PQR documents what occurred during welding of the test coupon and the result of the test coupon. The PQR gives suitability of weld for required mechanical properties e.g. strength and ductility. The tension test indicates the strength and the bend tests indicate ductility.

Please note the procedure qualification record cannot be revised otherwise the case for revising being typing error or misspelling. The PQR must include all essential variables (such as P number, F-number, A number, PWHT)  and supplementary essential variables (such as Group Number). The nonessential variables are not coded requirements for PQR.

When a construction code like ASME Code Section VIII Div I requires impact testing, the impact testing must be included in Welding Procedure Qualification Record technical testing. Normally you need to conduct two sets of impact testing, one set in the weld metal and one set in the heat-affected zone.

PQR test coupon

How to prepare a Procedure Qualification Record (PQR)?

After deciding the welding process(s), material type and welding consumables then a PQR need to be prepared. The construction codes (e.g. ASME Section VIII or ASME B31.3) may have restrictions, addition requirements or exemptions to ASME IX and you want to make sure you understand them before you start.  For example, ASME Section VIII Division 1 UG-84 has provisions that would make toughness testing mandatory for certain materials and thicknesses or UCS-56 or UW-2 has mandatory post weld heat treatment requirements.  Understanding these requirements before you create a PQR can reduce the number of procedure qualification tests that you will need for actual job.

So, after considering the requirements if any by the construction code next step is to make reference to QW-250 of ASME Section IX.  The tables in QW-250 make reference to all the essential, non-essential, special process and supplementary essential variables.  These variables are defined in QG-105.  As noted in QW-200.2, a PQR shall document all essential and when required supplementary essential variables.  This means that the PQR you create must as a minimum address the corresponding essential variables in the tables for the welding processes you have used in QW-250.  Supplementary essential variables become essential variables when toughness testing is required, typically from the referenced construction code and become non-essential variables when toughness testing is not required.  From a PQR standpoint non-essential variables are not required to be documented. 

Properly addressing essential variables can be issue as well.  For example stating N/A or not applicable to essential variables in a PQR document technically has not addressed the variable if it is applicable to your process.  The correct phrase would be not used, this clearly addresses the variable.

For all PQRs the base metal thickness range (QW-403.8) and P. No. (QW-403.11) are essential variables.   Section QW-451 provides qualification thickness ranges based on the test coupon that was used.  For example, a 0.375” test coupon will qualify the referenced WPS from 0.0625” to 0.75” in material thickness.  This thickness range can be affected by the welding process and other essential / supplementary essential variables referenced in QW-250, it is best to review all variables before you determine the thickness of your test coupon. 

An overlooked aspect of developing a PQR is nozzle or branch connection attachments.  Typically the thickness of the shell and nozzle of the welded joint will have different thicknesses.  Let’s say you qualify a WPS with a thickness range of 0.0625” to 0.75”, during fabrication you have to weld a nozzle with thickness of 0.2” to an ASME B16.5 blind flange that is 2” thick.  Can you do this?  The answer is it depends.  Section QW-202.4 details these requirements.

Base metals are assigned P-numbers to reduce the required number of welding procedures that are required.  For example P. No. 8, represents 304, 316, 321, 347, and more base metals.  Table QW-422 provides a complete list.

The welding electrode or welding filler metal selection is also main part of the PQR qualification.  Reviewing ASME II Part C is a great help, below is a table reference to easily locate the relevant SFA specification.

Onc you have prepared the PQR from, the next step is to decide the welding parameter ranges for the pWPS. You can choose welding parameters based on your experience or using reference material such as the arc welding handbook or the welding consumables handbooks.

Next step is to weld the Test coupon according to the pWPS.

Once satisfactory weld of the test coupon is completed, next the destructive testing requirements in QW-202 is to be done.  If successful, the result would be included in the PQR and then signed and dated by the fabricator to certify the results & PQR shall be called as qualified.
Click this link to find the Acceptance Criteria of Tension Test for Welding Procedure Qualification Record

Does changes to the PQR are allowed?

Changes to a qualified PQRs are permitted as outlined in ASME Section IX QW-200.2(c) (and the Introduction) but only editorial corrections or addenda, as long as an essential variable has not changed and the PQR can be revised.  Adding supplementary essential variable will require re-qualification of the PQR.  As PQR is an actual record of what happened during welding & what were its results, changes that can affects those results are not permitted.

When requalification of a WPS/ PQR is required?

The question of “When do I need to requalify my WPS?” is not asked that often, but it arise many times. A welding procedure specification (WPS) as we know is a set of instructions that if followed, will insure a sound weld.  A WPS will typically provide ranges rather than single values for some variables such as current, voltage, and travel speed.  Nonetheless, if the values used for making a weld are outside of the parameters of the WPS, then it has been violated by the WPS user.  

So, when should you requalify a WPS? The answer is always, when the code or specification require it. When doing code work, you should always reference the code you are working to for guidance.  Most codes have similar requirements as to when requalification of a WPS is necessary. In general, any change beyond the limits of the procedure qualification record (PQR) will require requalification. If any of these variables change consult your code or specification to see if you need to requalify a WPS based on the changes happened outside the qualified range.

Example for a WPS requalification requirements:

Following is an example of reviewing whether or not a requalification is necessary. XYZ Ltd. is doing work governed by the AWS D1.1, Structural Welding Code – Steel.  For a cost reduction and efficiency improvement measure the company decides to make the following changes to the existing qualified WPS:

  • Switch to .052” ER70S-6 MIG wire from .045” ER70S-6 wire for higher deposition rates in some areas.
  • Increase Welding amperage from 250A to 265A with .045” ER70S-6 wire to increase deposition rates in remaining areas.
  • Change from tapered nozzles to ¾” ID coupled with increase from 40cfh to 45cfh to reduce issues with porosity.
  • Switch their shielding gas mixture from 75% argon/25% CO2 to 90% argon/10%CO2 to reduce spatter and decrease grinding.
  • Some welds will be made vertical up to improve penetration and reduce leaks (using same parameters).

If we consider each of these changes individually here is how things would conclude. We reference  AWS D1.1, Structural Welding Code – Steel – Table 4.5 – PQR Essential Variable Changes Requiring WPS Requalification for SMAW, GMAW, FCAW, and GTAW and review each change.

  • Switch from .045” to .052” – Table 4.5(10) indicates that “any increase” in filler metal diameter shall require requalification.
  • Amperage increase from 250 to 265 staying with .045” wire – Table 4.5(12) requires requalification if the change in amperage exceeds 10%; therefore, we do not need to requalify in this case since a 15 amp increase only represents a 6% change.
  • Change in nozzle size and gas flow rate – Table 4.5 does not mention changes in nozzle size as an essential variable. However, when in doubt go to the engineer or to the customer for clarification. The change is gas flow rate is does not require requalification per Table 4.5(20). A change is only necessary if the flow rate goes up by more than 50% or is reduced by more than 20%.

It is important to consider the effects of changes here as well. A change in nozzle may not be an essential variable, but if the larger nozzle hampers access and requires the welder to run a longer contact tip to work distance this could decrease the amperage to the point which require requalification.

  • Switch from 75/25 to 90/10 argon/CO2 shielding gas – Table 4.5 (19) requires a change when the gas composition is changed exceeding code limits. In this case a change of more than 10% of the minor component requires requalification.

Also, this change allows ABC to go from globular transfer into spray transfer. This is a mode of metal transfer change which also requires requalification per Table 4.5 (14).

  • Addition of vertical up welds – requires qualification as well per Table 4.5 (30) which states that requalification is needed “for any pass from uphill to downhill or vice versa.”

Sound knowledge of the welding process and understanding of the code or specification involved is critical for right decision. 

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