6.1 Reviewing WPS and PQR per ASME Section IX

6.1 Reviewing WPS and PQR per ASME Section IX

ASME Section IX governs the qualification of welding procedures, welders, and welding operators. In the context of API 570, an in-service piping inspector must possess a strong understanding of how to review, cross-reference, and verify the validity of a Welding Procedure Specification (WPS) and its supporting Procedure Qualification Record (PQR). These documents form the technical foundation for any welding work performed during piping fabrication, repair, or alteration. An inspector's main goal when reviewing these documents is to ensure that all required variables are within the qualified ranges and that the mechanical properties of the weldment have been proven by testing.

The WPS and PQR Relationship

A Welding Procedure Specification (WPS) is a written, qualified instruction sheet that provides direction to the welder for making production welds in accordance with the construction or repair code. The WPS lists all the variables—essential, non-essential, and when required, supplementary essential—that the welder must follow to achieve a sound weld.

Conversely, the Procedure Qualification Record (PQR) is a historical record of the actual parameters used during the welding of a test coupon, along with the subsequent destructive test results. The PQR serves as the empirical proof that a specific combination of base metals, filler metals, welding processes, and heat treatments can produce a joint with acceptable mechanical strength and ductility.

A WPS cannot stand alone; it must always be supported by one or more PQRs. A single PQR can support multiple WPSs (e.g., a PQR welded with a certain filler metal can support multiple WPSs with different joint designs), and a single WPS can be supported by multiple PQRs (e.g., to cover a broader range of thicknesses), provided the essential variables align.

Essential, Non-Essential, and Supplementary Essential Variables

ASME Section IX classifies welding variables into three distinct categories:

• Essential Variables: These are parameters that, if changed, are considered to affect the mechanical properties (other than notch toughness) of the weldment. A change in an essential variable requires the qualification of a new PQR and the revision or reissue of the WPS. Examples include a change in the welding process (e.g., switching from SMAW to GTAW), base metal P-number, filler metal F-number, or a decrease in preheat temperature of more than 50°F.
• Non-Essential Variables: These are parameters that can be changed without affecting the mechanical properties of the weldment. They do not require a new PQR. A change in a non-essential variable only requires an update to the WPS. Examples include a change in joint design (groove type, bevel angle), cleaning method (brushing, grinding), or backgouging technique.
• Supplementary Essential Variables: These variables are only active when the construction code (such as ASME B31.3 for low-temperature service) requires notch toughness (impact) testing of the weldment. When impact testing is mandated, these variables behave exactly like essential variables, and any change requires a new PQR. Examples include changes in heat input, welding position (e.g., vertical uphill progression), or a change in the classification of the filler metal.

Base Metals: P-Numbers

To minimize the number of welding procedure qualifications required, ASME Section IX groups base metals with similar weldability, chemical composition, and mechanical properties under a single "P-Number" (QW/QB-422).

If a WPS is qualified for P-1, it cannot be used to weld P-8 base metals unless a supporting PQR has been qualified using P-8 test coupons.

Filler Metals: F-Numbers and A-Numbers

Filler metals are grouped to reduce procedure and performance qualifications.

• F-Numbers (QW-432) group electrodes and filler wires based on usability characteristics, which determine the ability of welders to make satisfactory welds with a given filler metal.
  • F-1: High-deposition, rutile-type electrodes (e.g., E6024).
  • F-2: Iron-powder, titania-type electrodes (e.g., E6013).
  • F-3: Cellulosic-type electrodes (e.g., E6010, E6011), commonly used for root passes.
  • F-4: Basic, low-hydrogen electrodes (e.g., E7018), which provide high ductility and resistance to hydrogen cracking.
  • F-6: Solid/cored wire, bare rod (e.g., ER70S-6, ER308L, ER80S-B2).
• A-Numbers (QW-442) classify the chemical composition of the deposited weld metal. An inspector must verify that the A-number of the filler metal on the WPS matches the PQR and is suitable for the design temperature and corrosion environment.

Thickness Qualification Limits (ASME Section IX Table QW-451.1)

One of the most critical checks during a WPS/PQR review is verifying the base metal thickness (T) and weld metal thickness (t) ranges qualified. For a standard test coupon of thickness t welded and tested:

• If coupon thickness t is between 1/16 in. and 3/8 in. inclusive, the qualified base metal thickness range T is 1/16 in. to 2t.
• If coupon thickness t is between 3/8 in. and 1.5 in. inclusive, the qualified range T is 3/16 in. to 2t.
• If coupon thickness t is ≥ 1.5 in., the qualified range T is 3/16 in. to 8 in. (or unlimited under specific conditions).

For example, if a PQR coupon is 0.250 in. thick, the maximum qualified base metal thickness on the WPS is 2 x 0.250 = 0.500 in. If production piping is 0.625 in. thick, this WPS is invalid for the job, and a different WPS with a thicker PQR coupon must be selected.

Tension and Guided-Bend Tests

The PQR must document that the test coupon passed visual examination and mechanical testing.

• Tension Test (QW-150): Two tension specimens are tested. The tensile strength must meet or exceed the minimum specified tensile strength of the base metal. If the specimen breaks in the base metal outside the weld or fusion line, the test is acceptable provided the strength is not more than 5% below the specified minimum tensile strength of the base metal.
• Guided-Bend Test (QW-160): Typically, four bend specimens (either transverse side bends, or face and root bends) are required. The specimens are bent around a mandrel to check for ductility and fusion defects. To pass, the bent surface must show no open defects exceeding 1/8 in. (3 mm) in any direction.

Review Checklist for Inspectors

When reviewing a WPS/PQR package for a piping repair or alteration, follow these steps:

1. Compare the base metal P-number of the production joint against the range qualified on the PQR.
2. Confirm the production wall thickness fits within the qualified base metal thickness range.
3. Verify the filler metal F-number and A-number are compatible with the base metal and design conditions.
4. Ensure the preheat and PWHT requirements on the WPS are supported by the PQR.
5. Verify the mechanical testing results (tensile and bend tests) are recorded and meet ASME Section IX minimum values.
6. Check if notch toughness is required; if so, verify that the supplementary essential variables (such as heat input and progression direction) are qualified on the PQR.