Guide to Weld Procedure Qualification Testing (U.S. Standards)

What is Weld Procedure Qualification and Why is it Important

Weld Procedure Qualification is the process of proving that a given welding procedure will produce a sound weld that meets quality and safety standards. In practice, a welding company writes a Welding Procedure Specification (WPS) – a document that describes how to make a weld (including parameters like materials, positions, voltages, etc.). This WPS must be supported by a Procedure Qualification Record (PQR), which is a formal record of a test weld that was performed and then rigorously tested to ensure the procedure produces a good weld. Essentially, the PQR documents the welding variables used and the results of all required tests, demonstrating that the procedure can achieve the desired weld properties. Major U.S. codes (such as AWS D1.1 for structural welding and ASME Section IX for pressure vessels and piping) require that new WPSs be qualified by testing unless they meet specific pre-approved conditions.

Why is this important? Having a qualified weld procedure is critical for safety and quality. It ensures the weld has the necessary strength, ductility, and toughness for its intended application. For example, pressure vessels, pipelines, buildings, and bridges all rely on welds that must perform under stress and sometimes extreme conditions (like low temperatures or high pressures). A qualified procedure gives confidence that the welds will not fail in service. In fact, many applications (boilers, pressure vessels, structural steel, etc.) legally require welding to be done with qualified procedures. By performing procedure qualification tests, a manufacturer demonstrates that using the specified procedure will result in welds with properties that meet or exceed code requirements. This is fundamental to quality assurance in welding.

It’s worth noting that welder performance qualification is a related but separate process. Welder qualification tests ensure that an individual welder has the skill to deposit sound welds using an approved procedure. Unlike procedure qualification (which involves a battery of mechanical tests on a procedure test coupon), a welder’s test is typically simpler – for instance, a welder might weld a test plate which is then inspected by X-ray or cut into strips for bend tests. If the weld coupons pass visual and bend tests (showing no cracks or defects), the welder is qualified for that WPS. In summary, procedure qualification verifies the process (the WPS), and welder qualification verifies the person – both are important for compliance with codes like AWS and ASME, ensuring that sound procedures are used and that welders can execute them properly.

When is a Full Qualification Needed?

A welding company would perform a full procedure qualification (WPS/PQR) whenever they are implementing a new welding procedure that has not been previously proven by testing. According to the codes, certain changes in the welding procedure variables mandate a new qualification. These variables (called essential variables) include things like the base material type or grade, the welding process (e.g. SMAW vs. GMAW), filler metal type, material thickness or diameter, and sometimes welding position. If you change any essential variable beyond the limits allowed by the code, the existing procedure is no longer valid and a new procedure qualification test must be carried out. For example, an increase in material thickness beyond the qualified range, or switching to a different alloy, would require re-qualifying to ensure the welds still meet requirements.

In U.S. codes, the need for qualification is often clearly defined. ASME Section IX (for pressure vessels, boilers, and piping) generally requires a procedure qualification test (PQR) for any WPS – there are no “prequalified” WPSs in ASME, so every procedure must be backed by testing. AWS D1.1 (Structural Welding Code), on the other hand, provides a set of prequalified WPSs for common joint configurations and materials; if you strictly follow those prequalified rules, you may not need to do a PQR test for those cases. However, if you go outside the prequalified conditions (for instance, using an unlisted steel or a new welding technique), then AWS D1.1 requires you to qualify the procedure by testing. In summary, a full qualification is needed when you are using any new or unproven welding procedure, or when required by project specifications or contract. Many customers and regulatory bodies will insist on seeing the PQR documentation before work begins, especially in critical applications.

Major Tests Involved in Procedure Qualification

When qualifying a welding procedure, the welded test coupon undergoes a series of mechanical and metallurgical tests to verify that the weld meets code criteria. Each test examines a different aspect of weld quality (such as strength, ductility, toughness, or chemistry). Collectively, performing all these tests is often referred to as a “weld procedure qualification test”. The exact test requirements can vary by code and by the application; for example, some codes or project specifications might add specific tests. Below is a table summarizing the main tests commonly performed and what they check for:

Test	What it Checks
Tensile Test	Measures the tensile strength of the welded joint (ensures the weld metal and joint are as strong as required, typically matching or exceeding the base metal’s strength).
Guided Bend Test	Checks ductility and fusion of the weld by bending the specimen – reveals lack of fusion, cracks, or brittleness (ensures the weld can stretch and doesn’t crack under bending).
Charpy Impact Test	Measures toughness – the ability of the weld metal to absorb impact energy without fracturing, especially at low temperatures (ensures the weld isn’t too brittle for cold or dynamic service).
Hardness Test	Measures the hardness of the weld metal and Heat-Affected Zone (HAZ), which correlates to properties like strength and brittleness; ensures the weld/HAZ isn’t too hard (which can indicate brittleness or crack susceptibility) or too soft.
Chemical Analysis	Determines the chemical composition of the weld deposit (and sometimes base metal) to verify the correct alloy content and that no detrimental elements are present; confirms that the filler metal and dilution achieved the intended chemistry (e.g. important for alloy specifications and code grouping like ASME “A-No.” classification).

In addition to the above, other tests may be included depending on the situation. For example, a macroetch examination (polishing and acid-etching a cross-section of the weld) is often done, especially for welder qualification or for fillet weld procedures, to check penetration and fusion profile. Also, before destructively testing the coupon, codes often require non-destructive examination (NDE) such as visual inspection and sometimes radiography or ultrasonic testing to ensure the weld test coupon has no major defects that would invalidate the mechanical tests. All these tests together give a comprehensive picture of weld quality. Below, we explain each main test in simple terms and note how they demonstrate weld quality and compliance.

Tensile Testing (Tension Test)

A tensile test involves pulling a sample of the welded joint until it breaks, to measure the weld’s strength. From the procedure qualification coupon, one or more tension test specimens are machined (often a rectangular specimen that includes the full weld cross-section). Each specimen is placed in a tensile testing machine, which applies a uniaxial pulling force. The machine pulls the sample steadily until it fractures. The maximum force the sample sustains is recorded, and from this and the cross-sectional area of the specimen, the tensile strength is calculated (force divided by area gives stress).

The tensile strength result tells us whether the weld metal and the welded joint are as strong as they need to be. For instance, design codes typically require that the weld’s tensile strength meet or exceed the minimum tensile strength of the base metal or the filler metal classification. A passing test usually means the specimen broke in the base metal (away from the weld) or, if it breaks in the weld, it did so at a stress above the required minimum. This ensures the weld is not the weak link in the structure. As an example, AWS D1.1 specifies two transverse tensile tests for a procedure qualification coupon and requires that the ultimate tensile strength meet the base metal’s minimum specification (or the weld metal’s spec) as applicable. Tensile testing verifies the load-carrying capacity of the weld: if the weld can withstand at least the expected service loads (usually a safety margin is included), it passes.

In simple terms for a welding contractor: the tensile test checks that the weld won’t pull apart. If your welding procedure is sound, the welded joint should be as strong as the metal around it. Tensile tests give a numeric value (e.g. the weld broke at 70,000 psi), which you can compare against standards. Failing a tensile test (the weld breaking at too low a load or in a brittle manner) indicates the procedure might produce weak welds – perhaps due to improper filler metal, lack of fusion, or other issues. Thus, tensile testing is a fundamental part of procedure qualification to ensure strength compliance.

Guided Bend Testing

A bend test is a qualitative mechanical test that stresses the weld in bending to reveal any weld discontinuities or brittleness. In a guided bend test, a strip specimen containing the weld (usually 6 to 12 inches long) is supported at both ends and bent into a “U” shape by a plunger or former. There are several types of bend tests: typically for procedure qualification, transverse bend tests are used, where the weld is oriented transverse to the length of the specimen. The common ones are: face bend (weld face on the outside of the bend), root bend (weld root on the outside of the bend), or side bends (for thick welds, the specimen is turned sideways so the full thickness is tested). AWS D1.1, for example, requires four bend specimens – either two face and two root bends, or four side bends – from each procedure test coupon.

During the test, the specimen is bent 180° or until a specified bend angle is reached. The outer side of the bent specimen (the tension side) is then inspected for cracks or open defects. A successful bend test shows no cracks or tears on the outside greater than a certain size (typically 1/8 inch is a common acceptance criterion in many codes). What does this prove? It demonstrates the weld’s ductility and soundness. A good weld will bend almost double without cracking, meaning it has fused well with the base metal and isn’t too brittle. If there are internal flaws like lack of fusion, slag inclusions, or cracks, they will often open up and become visible on the bent surface under the severe bending strain. This makes bend testing very effective at revealing problems that X-ray or ultrasound might miss – it’s a direct proof of the weld’s toughness and quality.

Diagram of a weld bend test: (top) a welded plate coupon before bending, and (bottom) the coupon bent into a “U” shape. The weld in this example has not cracked on the outside of the bend, indicating good ductility. Bend tests will expose welding defects or brittle welds by cracking – if a weld has internal flaws or is too brittle, cracks will appear on the outside of the bend.

For welding contractors, the bend test is one of the clearest proofs of a sound weld. You physically force the weld to bend upon itself. If it bends without opening up, it means the weld metal and the heat-affected zone can deform along with the base metal – a sign of a quality weld. Codes use bend tests in both procedure and welder qualifications because they are relatively simple and effective. As a note, a welding procedure that produces welds which consistently fail bend tests (by cracking) is unacceptable; it could indicate issues such as an improper welding technique, wrong filler, or excessive hardness in the weld/HAZ leading to brittleness. Bend testing ensures adequate ductility and fusion, which correlates to the weld’s ability to tolerate stress and strain in service without fracturing.

Charpy Impact Testing (Notch Toughness Test)

The Charpy V-Notch impact test is a test for toughness, specifically how much energy the welded material can absorb when suddenly loaded (impacted) at a given temperature. Toughness is the material’s ability to absorb energy without fracturing. In certain applications, especially low-temperature service (like bridges in cold climates or pressure vessels for cold fluids), having sufficient toughness is critical to prevent brittle fracture. A welding procedure may need to be qualified with Charpy testing if the design requires a minimum toughness. For instance, AWS D1.1 will require impact tests on the procedure if the structure has notch toughness requirements (often stipulated for seismic or cold-weather applications), and ASME codes require it for certain materials or services (where the construction code or contract specifies notch toughness criteria).

In a Charpy test, a small bar specimen (typically 55 mm × 10 mm × 10 mm) is machined from the weld – usually with the notch in the weld metal or the weld fusion line area – and cooled or heated to a specified test temperature. The specimen has a V-notch cut in it. During the test, the specimen is placed on supports in the Charpy tester and a heavy pendulum hammer swings down to strike the notched side of the sample. The hammer breaks the specimen, and a dial or digital display measures how much energy (in ft-lbs or Joules) was absorbed in the breaking process. A tougher material will absorb more energy (meaning the hammer is slowed down more), whereas a brittle material absorbs little energy and the specimen snaps easily. Typically, multiple specimens (e.g. three) are tested to get an average energy value at the given temperature.

Illustration of a Charpy V-notch impact testing machine. A pendulum swings down from a set height to strike the notched specimen. The specimen (supported as a simple beam) fractures, and the pendulum rises to a lower height on the other side – the difference in height (and thus energy) is recorded on the dial. The inset (upper left) shows a sample with a V-notch. This test determines how much energy the material absorbs in fracturing, which is a measure of its toughness.

What does Charpy testing prove? It demonstrates the brittle or ductile behavior of the weld at the test temperature. If a welding procedure produces weld metal that is too brittle (for example, due to high carbon content or improper heat treatment), the Charpy energy will be low and the sample may break with a crystalline (brittle) fracture appearance. A good, tough weld will show higher energy absorption and often a more fibrous (ductile) fracture. Codes specify minimum impact energy values for given temperatures – e.g., a bridge weld might require >= 20 ft-lbs at -20°F in the weld metal and HAZ. By doing Charpy tests in procedure qualification, we verify that the procedure (with the chosen materials and parameters) can achieve the required notch toughness. This is particularly important for preventing brittle fracture in service. Welding contractors should understand that if a job or code calls for “CVN testing” or “impact-tested WPS,” it means the procedure qual will include Charpy tests. Not all welds need this – mostly those subject to shock loads or low temperatures – but when required, it’s a crucial quality check. Failing Charpy tests would mean the procedure might need adjustments (different filler, higher preheat, etc.) to improve weld toughness.

Hardness Testing

Hardness testing checks how hard the weld metal and heat-affected zone are. Hardness is measured by pressing a hardened indenter into the material and measuring the size or depth of the indentation. In welding, hardness tests (typically using Vickers or Rockwell or Brinell methods) are sometimes performed on the cross-section of a weld. The purpose is to ensure that the weld and the surrounding HAZ are not excessively hard or soft for the intended service. Why is this important? Hardness correlates with properties like strength and brittleness – a very hard HAZ might indicate martensite formation which could be brittle and crack-prone (especially in hydrogen-containing environments), while a very low hardness might indicate an overly soft weld that lacks strength. Hardness testing enables evaluation of material properties such as strength, ductility, and wear resistance.

For most structural or pressure applications, hardness testing is not a default requirement in procedure qualification, but it becomes critical in certain cases. For example, in qualifying wear-resistant overlay procedures (hardfacing), the goal is to achieve a high-hardness surface, so the procedure qualification will include hardness tests to ensure the deposited layer meets the required hardness. ASME Section IX specifically mandates hardness testing when qualifying a procedure for a Wear-Resistant Overlay (WRO) – instead of tensile tests, one must take hardness readings of the overlay and typically do a macroetch. In contrast, a Corrosion-Resistant Overlay (CRO) (like stainless steel cladding) procedure is qualified with bend tests for bonding. Hardness testing is also commonly specified for weld procedures on certain high-strength steels or for sour service environments (to ensure the hardness is below a threshold to avoid hydrogen cracking). For instance, pipeline welding procedures intended for sour service might require verifying that weld and HAZ hardness do not exceed 250 HV or a similar criterion.

Performing a hardness test on a weld cross-section usually involves polishing a small area of the weld, HAZ, and base metal, then using a microhardness tester (like Vickers hardness tester) to take indentations across those regions. The results tell the hardness profile of the weldment. If a particular weld area comes out too hard, it could be a sign of problems (like inadequate preheat or using the wrong filler causing a hard brittle microstructure). For the welding contractor, think of hardness testing as a check on metallurgical properties: a properly executed procedure should produce a weld that is hard enough to be strong but not so hard that it’s brittle. For example, a PQR on a quenched and tempered steel might include hardness tests to ensure the HAZ did not exceed the steel’s original hardness (maintaining toughness). In summary, hardness testing in weld procedure qualification is about verifying the metallurgical soundness of the weld – it’s used when hardness matters for service performance or code compliance.

Chemical Analysis of Weld Metal

Chemical analysis in the context of weld qualification is done to verify the chemical composition of the weld deposit. This is important for confirming that the weld metal chemistry is within desired limits, which affects mechanical properties and corrosion behavior. Weld chemistry is mainly determined by the filler metal composition and any mixing with the base metal (dilution). In many cases, if you use a known filler (say an E7018 electrode), and you weld on a similar base metal (mild steel), the chemistry of the weld will fall in a predictable range. The code may not require an explicit chemical analysis for every procedure qualification in such cases. However, there are situations where analysis is required or very useful, such as:

Dissimilar metal welding: When joining two different alloys (e.g., stainless steel to carbon steel), the resulting weld chemistry can be complex. A chemical analysis will tell you the actual composition of the weld deposit, which is used to verify that it meets any project requirements or to determine the appropriate PQR classification. In ASME Section IX, for example, weld metal chemical composition is categorized by A-Numbers, which group weld metals by their predominant chemical constituents. If a filler metal’s A-Number is not known or you suspect dilution might alter the chemistry, the code allows determining the A-Number by doing a chemical analysis of the weld metal from the qualification coupon.
Alloy specifications: Some procedures involve high-alloy materials where maintaining a certain composition (e.g., Cr, Ni content in stainless or low alloy steel welds) is critical. A chemical analysis ensures the weld deposit meets the specified alloy grade. For instance, if qualifying a procedure for Inconel welding, you might do an analysis to ensure no excessive iron dilution into the weld.
Diffusible elements or impurities: Occasionally, procedures must limit elements like carbon, sulfur, or phosphorus. Testing the weld metal chemistry can verify these are below required maxima. This can be part of a PQR in critical applications.

Chemical analysis is typically done by methods such as Optical Emission Spectroscopy (OES) or by sending a sample for lab analysis. The results are reported as percentages of elements in the weld metal. In ASME PQR documentation, if the weld metal analysis was performed, it would be recorded and the appropriate A-Number assigned (for example, a carbon-steel weld deposit might come out as A-No. 1 if it’s a plain carbon steel chemistry). The American Welding Society (AWS) codes for structural welding don’t usually require chemical analysis for standard carbon steel welds, but certain AWS specifications (like for welding electrode classifications or special alloys) might call for it.

In practical terms, welding contractors might engage a certified lab to do a Positive Material Identification (PMI) on the welds from the test coupon. This is essentially a quick chemical analysis, using handheld XRF or OES, to confirm the metal composition. The benefit is ensuring that the procedure with the chosen filler metal yields the correct chemistry, which in turn correlates to meeting mechanical property requirements. Chemical analysis in a PQR gives an extra layer of confidence that the weld is “what it’s supposed to be” chemically. It can catch issues like accidentally using the wrong filler or unexpected dilution from the base metal. Overall, while not every procedure qualification will include chemical analysis, it is a key part of qualifications for certain materials and is often required by codes when the alloy content defines the performance (for example, hardfacing overlays or corrosion-resistant overlays must be checked to ensure the chemistry meets the intended alloy specification).

Compliance with Codes and Standards

The above tests are all commonly mandated or referenced by major U.S. welding standards:

AWS Codes (American Welding Society): AWS D1.1 (Steel Structural Welding Code) outlines that a procedure qualification (PQR) for a groove weld requires two transverse tensile tests and four guided bend tests (face and root or side bends) from one welded test plate. If notch toughness is required by the design, Charpy V-notch impact tests must also be done per AWS D1.1’s criteria. AWS D1.5 (Bridge Welding Code) and others have similar requirements. AWS also often calls for macroetch tests for fillet weld procedure qualifications. The AWS codes allow using prequalified WPSs (no PQR needed) only in specific scenarios; otherwise, all new procedures must pass the mechanical tests. Welder qualifications per AWS usually involve bend tests or radiographic examination of a test weld, but not the full range of procedure tests.
ASME Boiler & Pressure Vessel Code (Section IX): ASME Section IX is a qualification standard that specifies how welding procedures and welders are qualified for applications like pressure vessels (ASME Section VIII), piping (ASME B31 codes), etc. Section IX requires at least two tension tests and two bend tests for a groove weld procedure qualification (more specimens for thicker coupons), unless additional tests are mandated by the referencing construction code. If the construction code or material specification requires notch toughness, then Charpy impact testing becomes a supplementary essential variable – meaning the procedure must be qualified with impact tests and meet the required energy values. ASME also has special provisions: for example, as noted earlier, welding corrosion-resistant or hardfacing overlays have unique test requirements (bend tests for CRO, hardness for WRO). All these are documented in the PQR. ASME Section IX does not explicitly require chemical analysis in most cases, but it defines the A-Number system for recording weld metal chemistry and allows it to be determined by analysis if needed. So while a standard carbon steel procedure might skip a chemistry test and simply record “A-No. 1” (from using an E7018 electrode), a procedure involving unknown dilution might include an analysis to be sure of the A-Number.
API Codes (American Petroleum Institute): For pipelines (API 1104) and other petroleum industry applications, procedure qualification also involves tensile tests, bend tests, and sometimes nick-break tests or hardness tests depending on the material and service (e.g., sour service pipelines often require hardness testing of the weld and HAZ to ensure crack resistance). The philosophy is similar: prove the procedure makes sound welds via mechanical testing.

In short, whether it’s AWS, ASME, API, or other codes, the principle is the same: weld procedure qualification = welding a test coupon with the new procedure, then cutting it up and testing it to destruction to check all critical properties. By doing so, the fabricator demonstrates compliance with the code’s requirements for weld quality.

Benefits of Using Certified Testing Labs

Welding contractors and fabricators often turn to certified third-party testing laboratories to perform these qualification tests. There are several benefits to using a certified lab for weld procedure qualification:

Accuracy and Reliability: Certified labs (especially those accredited to ISO/IEC 17025 for testing) have calibrated equipment and qualified technicians to ensure accurate results. For example, a lab accredited to ISO 17025 has demonstrated that it operates competently and generates valid test results, which gives confidence in the data. Many reputable weld testing labs in the U.S. hold such accreditations and even specific approvals (some are AWS Accredited Test Facilities for welder testing). This means they follow strict procedures for testing, so the results will be trusted by clients and inspectors.
Compliance and Expertise: A good laboratory will be well-versed in the code requirements (AWS, ASME, etc.) and can ensure that the testing is done in accordance with the standard – including proper specimen preparation, test methods, and reporting. This is critical because a procedure qualification is only valid if the testing was done per the code’s specifications (for instance, using the correct dimensions for bend specimens, performing tensile tests per ASTM standards, etc.). Labs that specialize in weld testing often have Certified Welding Inspectors (CWIs) and engineers on staff who can write the WPS, supervise the welding of the test coupon, and conduct or subcontract the mechanical tests properly. Their expertise helps avoid mistakes that could invalidate a test.
Impartial Verification: Using an independent lab provides an unbiased verification of weld quality. The lab’s test report becomes objective evidence that your procedure met the requirements. This can be very important when submitting qualification results to clients or regulatory authorities. They are more likely to trust an independent lab report than an in-house test. In many cases (e.g., for code stamp jobs or government work), third-party witnessing or testing is explicitly required.
Efficiency and Equipment: Not all contractors have the specialized equipment (like a tensile test machine or a Charpy impact tester or a hardness tester) to perform all these tests. Certified labs have the necessary machines and can perform the tests under controlled conditions. They also handle the machining of test specimens (which itself must meet standards). Outsourcing this task is often more efficient and ensures it’s done right. Labs can usually return results quickly and even provide guidance if a test fails (helping diagnose why a procedure might not have passed, so you can adjust and re-test).
Documentation and Certification: A lab will provide a formal report of the test results, and often they can help prepare the PQR document in the format that codes require. This documentation is essential for your records and for auditors. Having the PQR certified by a reputable lab adds credibility. It shows due diligence in your quality program.

In summary, while it’s possible for large companies to do some testing in-house, most welding businesses find that using a qualified lab is the best way to get their welding procedures qualified. The lab essentially becomes a partner in your quality assurance process – making sure your welds are tested thoroughly and correctly. The investment in proper testing pays off by preventing the use of unsound procedures and by giving your company and your clients confidence that the welding procedures will produce safe, high-quality welds.

By understanding these tests and why they’re performed, welding contractors can better appreciate the process of weld procedure qualification. It might seem like a lot of hoops to jump through – cutting up perfectly good welds and breaking them – but this destructive testing regimen is there to ensure that when those procedures are used in production, the welds will hold up under real-world conditions. In critical industries, doing procedure qualification is not just a paperwork exercise, but a vital part of quality control and compliance. Once a WPS is qualified (backed by a successful PQR), it becomes a proven “recipe” you can trust for producing consistent weld quality, as long as welders follow it and are properly qualified. Each of the tests (tensile, bend, impact, hardness, chemical) checks a different quality aspect, and together they give a comprehensive verification that the welding procedure is fit for service according to U.S. codes like AWS and ASME. Using certified labs and following the code rules ensures that the qualification process itself is robust and credible. Ultimately, a well-qualified welding procedure helps prevent failures in the field, protects public safety, and saves money by getting the job done right the first time.

Sources:

Quality Testing Inc. – Weld Procedure Qualification Testing (overview of tests and definitions)
Dynamic Labs – Welding Procedure Development & Qualification (importance of qualification)
TWI (The Welding Institute) – Welding Procedure (essential variable changes require re-qualification; AWS vs ASME requirements)
Simon Forensic – Weld Testing (QA/QC weld procedure and welder qualification)
Eng-Tips Forum (Al, CWI) – AWS D1.1 Procedure Qualification Requirements (tensile and bend specimens from one coupon)
ESAB – Introduction to Destructive Weld Testing (transverse tension test and bend test purpose)
Nucor – What is the Charpy Impact Test and Why is it Important? (toughness definition and Charpy overview)
AQC Inspection – Welding Procedure for Overlay (Hardness test requirements in ASME for overlays)
Welding & NDT Resource – ASME IX: P-Number, F-Number, A-Number (weld metal A-Number explained as chemical composition of weld deposit)
WeldIntegrity.no – Hardness Testing (role of hardness testing in evaluating material properties like strength and ductility)
WTTI – Welder & Procedure Certification (use of ISO 17025 accredited labs and AWS Accredited Test Facilities for qualification testing)