A Simple Guide to Understanding Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR)

Weld quality is not just determined by the welding inspector visually judging the weld and saying, "Oh yeah, that's a good weld."

There are governing documents that the welding inspector, welding engineer, and design engineer need to have in order to have a good-quality weld.

Apart from the codes, standards, specifications, and contract documentation that the welding inspector needs to adhere to, there are other pre-welding documents that need to be studied.

This is where the Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR) come in.

Welding Procedure Specification

A WPS is a written document that provides direction to the welder or welding operator for making production welds in accordance with the code or standard requirements.

Let's take a look into the composition of the WPS:

This is a sample WPS, a bit overwhelming, isn't it? Let's dive into the details one by one.

• Welding Processes - whether the welding is SMAW, GMAW, GTAW, SAW, etc.
• Base metal and specifications - type or grade of the material to be used in the production welding, designated by a P-number.
• Filler metals - indicated are the type, classification, composition and storage of filler metals, designated by F-number.(In summary, P-number is for the base metal, F-number is for the filler metal, A number for the weld metal)
• Type of current and current range, arc voltage and travel speed - these parameters determine the heat input. Varying one or the other may result in different weld deposition and penetration.
• Joint design - sketch of the joint, indicated here are the groove angle, root opening, root face and other joint dimensional parameters
• Positions of welding
• Preheat and interpass temperature - for multi-pass welds, preheat temperature is the temperature of the previously deposited weld metal immediately prior welding. Interpass temperature is the temperature in the previously deposited metal immediately before the next pass is started.
• Heat input - this is the product of the current, voltage and weld travel speed
• Peening - working of metals by impact blows, improving its fatigue life
• PWHT (Post Weld Heat Treatment) - subsequent heat treatment after welding to remove residual stresses. Includes holding time and temperature range.
• Shielding gas - some welding process requires an external source of shielding gas such as GTAW and GMAW.
• Welding technique - this is the manner in which the welder applies the weld i.e., string and/or weave

After the engineer defined the welding procedure specifications, these specifications need to be qualified if the weld will do what it intended.

This is where the PQR comes in.

Procedure Qualification Record

PQR or Procedure Qualification Record tests or establishes the properties of the weldment and not the skill of the welder.

Though most codes will consider the welder who performs the welding to be automatically qualified the document is not meant to judge the welder's skills.

The aim of the document is to demonstrate that the materials and methods prescribed in the specification will produce a weld joint with the mechanical properties that will meet the application.

Here are the three general approaches to procedure qualification:

1. Prequalified procedures
2. Actual procedure qualification testing
3. Weld mock-ups

PREQUALIFIED PROCEDURES

Let's first discuss the prequalified procedures. The best example here is the prequalified WPS from AWS D1.1 Structural Welding Code. This system is unique because there is no need to perform the actual qualification testing as long as it is within the prescribed limits.

AWS D1.1 recognizes the processes SMAW, SAW, GMAW, and FCAW prequalified with their long record of proven satisfactory performance.

Some parameters in AWS D1.1 which has prescribed limits for a prequalified WPS are as follows:

• Base metal/filler metal combinations
• Electrode diameter
• Current
• Root and fill pass thickness
• Single pass fillet weld size
• Single pass layer width

The limits of these parameters depend upon the welding position, type (fillet, groove, etc.) and the welding process.

ACTUAL QUALIFICATION TESTS

Two standards immediately come to mind for the qualification tests, these are ASME IX Welding and Brazing Qualifications and API 1104 Standards for Welding of Pipelines and Related Facilities.

They provide qualification procedures before the actual production weld starts.

Note that the difference between ASME and API is that in ASME, procedure qualification done in the flat position qualifies procedure done in all positions.

While in API, the procedure must be qualified in the specific position depending on the job requirements.

Similar to the AWS, these two standards dictate the extent of a given procedure qualification or else another qualification procedure must be developed.

In both of these systems, they will list certain essential variables. These essential variables dictate the extent of a given procedure qualification.

Basically, the essential variables are the ones that if changed in a welding condition, will affect the mechanical properties of the weld

These essential variables are:

• Change in P-number (base metal)
• Base metal thickness
• Filler metal types and sizes
• Specific welding techniques
• Welding process
• Pre-heat and PWHT

These essential variables are features of the weld that if changed significantly will require a new welding procedure to be established.

There are other variables in welding procedures:

Supplementary variables as mentioned in QW-251 are the essential variables required for metals whose referencing code, standard, or specification requires toughness test and are in addition to the essential variables for the welding process

Non-essential variables in the meantime are variables that if changed in the WPS may be made without requalification.

Examples of non-essential variables are:

• Arc voltage - minor change in arc voltage will not change the heat input or chemistry of the weld deposit
• Welding current - for example in SMAW, the electrode diameter is restricted to a narrow range of current, if it is set above or below the manufacturer's recommendation then it will yield unacceptable results. If the welder used an electrode diameter that is within the amperage range then the current is a nonessential variable.
• Travel speed - for a given electrode diameter, the travel speed is largely dependent on the melt-off rate of the electrode, which is dependent of the current.

Note that the heat input is a supplementary essential variable since it is a factor of determining notch toughness, so the arc voltage, current and travel speed must be within its specified limits. Other examples of supplementary essential variables are the pre-heat and post-heat treatment, change in welding process and others.

Notch toughness by the way is the ability of the material to absorb energy in the presence of a flaw.

Once these variables have been defined for a certain procedure, an actual test coupon is welded. In ASME, it can be a plate or a pipe, in API the coupon is tubular. These are then destructively tested based on the requirements.

1. Bend test - conducted to evaluate the ductility and soundness of weld joints. Soundness is defined as the freedom of the weld from discontinuities and defects.
2. Tension test - conducted to evaluate the strength and ductility of not just the weld metal, base metal, and the weldment.
3. Fracture toughness test - a test to determine the resistance of the extension of a crack in a metal. Most common is the Charpy V-notch impact test.
4. Nick break test - used almost exclusively for pipelines as described in API 1104. It judges the soundness of the weld by fracturing the specimen through the weld.

Now, that we have outlined the variables and the required tests for the qualifying the weld, here is a summary of the steps needed to qualify a WPS:

1. Select the appropriate welding variables
2. Check the equipment and materials for suitability.
3. Monitor weld joint fit-up and actual welding. Record all important variables such as current, voltage etc.
4. Test and evaluate the specimen as prescribed in the appropriate standard.
5. Review test results for compliance with the applicable code or standard
6. Release approved procedure for production
7. Qualify individual welders in this specification.
8. Monitor the use of that procedure during production. Welding inspector shall provide constant feedback to the engineer regarding the performance of the specifications.

WELD MOCK-UPS

These tests are done through the use of special test weld mockups. These are used for complex weldment configurations.

The conditions where this might arise are high levels of restraint, weld joint inaccessibility, and welds that are difficult to evaluate using a standard qualification test.

In summary, the procedure qualification record qualifies what's in the welding procedure specifications. The welding inspector or engineer needs to be aware of the essential variables if in case there are changes in the welding variable, it can be concluded that a new qualification record must be accomplished.

For a video lesson regarding WPS in summarized form, please see the video below.

If you want the ultimate guide on how to write a WPS and PQR based from ASME IX, click the video right here!

You can check out my free course right here about the welding inspector and welding safety practices which are part of the fundamentals part of the CWI exam, it is a 1 hour long video lecture on Udemy! Sign up now!