Reviewing Welding Procedures—Checklists for Nuclear Power Systems

According to American Society of Mechanical Engineers (ASME), boiler and pressure vessel code (BPVC) Section IX, American Welding Society (AWS) D1.1, AWS D1.6, and other welding codes, each manufacturer or construction contractor is mandated to conduct tests as prescribed by these codes to qualify the welding procedure specifications (WPSs). Nonetheless, numerous engineering cases and project management experiences indicate that the owner or project management organization must actively engage in reviewing and monitoring the WPSs of the manufacturer or contractor to enhance the project's success [1–3].

For example, Roy Christensen, a veteran in the welding industry at KT Project, emphasizes that many projects inadequately plan for their WPS reviews, thereby posing challenges to the project. Therefore, smart projects should involve the owner or project management organization in actively reviewing and monitoring the welding processes employed by the manufacturer or construction contractor.

In the nuclear power industry, welding stands out as a crucial special process delineated in Requirement 9 of the ASME NQA-1 Part I. According to Section 300 of Requirement 9, an organization conducting the special process bears the responsibility to adhere to approved procedures and processes [4]. However, as detailed in the preceding paragraph, nuclear power architecture and engineering (AE) companies within the nuclear power sector conduct thorough evaluations of procedure qualification records (PQRs) and WPSs for safety-related structures, systems, and components (SSCs) to ensure effective control of the welding process. This practice is essential for robust compliance with ASME NQA-1 requirements governing special processes.

Typically, manufacturers or construction contractors submit PQRs and WPSs to the AE Company. Subsequently, the AE Company's welding engineer reviews these documents and provides feedback through review comment sheets to the manufacturers or construction contractors. If the review comments necessitate improvements or modifications to the PQRs and WPSs, the authors of these documents at the manufacturers or construction contractors are required to enhance or modify them accordingly and resubmit them to the AE Company for further review. Only upon receiving an acceptable opinion from the AE Company will the PQRs and WPSs be approved for use in construction.

Recent years have witnessed a surge in China's commitment to achieving carbon peaking by 2030 and carbon neutrality by 2060, necessitating an increased deployment of nonfossil energy sources, including nuclear power. This surge has resulted in a notable uptick in the number of new nuclear power units in China. As a consequence, numerous new manufacturers, construction contractors, and technical personnel have entered the nuclear power industry. Due to their unfamiliarity with codes and design requirements, coupled with a lack of manufacturing and construction experience, the quality of welding procedure qualification documents has faced certain challenges. This has led to an elevated incidence of issues discovered during the document review process.

The discussions presented in this paper are rooted in the engineering practices of the Advanced Passive Pressurized Water Reactor, designed in accordance with ASME Codes.

In practical terms, the construction of a single nuclear power unit necessitates 500–600 PQRs and WPSs including welding processes according to ASME Codes and AWS D1.1 or AWS D1.6. Among these, documents qualifying in accordance with ASME codes constitute around two-thirds of the total. (This article focuses on this to expound.)

Drawing from Roy Christensen's engineering expertise, a summary review ensures the suitability and accuracy of the WPS for the intended application. Typically, such reviews are completed within an hour. Conversely, a comprehensive review entails a meticulous examination of all WPS details and variables, encompassing PQRs and associated documents, to ascertain compliance with relevant construction codes, project specifications, and other stipulations. This thorough process may span from 4 to 8 h [2,3].

This scenario aligns with the author's own engineering experience. Naturally, the specific duration required for the review hinges on factors such as the content complexity, document length, and the reviewer's level of expertise.

Ideally, the preparation process should yield accurate results in the initial attempt. However, if issues are detected during the review, necessitating subsequent rectification, it not only amplifies the workload for reviewers and preparers but also inevitably casts a negative impact on related work progress.

Over years of engineering practice, numerous welding engineers have crafted various WPS and PQR checklists. However, these compilations merely constitute basic adaptations of ASME BPVC Section IX, specifically QW-250 “Welding Variables” and its associated tables. Similarly, this study employed such checklists to aid in the review of PQRs and WPSs.

While the primary purpose of QW-250 and its tables is to delineate variable requirements for WPS, they are better suited for guiding welding engineers in conducting welding procedure qualifications [5,6].

However, when these resources are solely repurposed as checklists for PQR and WPS reviews, welding engineers still find it necessary to refer to specific provisions from other articles within Section IX.

Furthermore, these checklists often lack efficient correlation between WPS and PQR reviews, thereby limiting the enhancement of review efficiency.

Additionally, their scope is limited to assessing compliance with ASME BPVC Section IX, neglecting the need for PQR and WPS checklists that adhere to other sections of ASME Codes and the design requirements applicable to product weld joints.

To address the aforementioned challenges, the qualification rules and requirements of PQRs and WPSs are translated into intuitive descriptions, assessments of correctness, or numerical comparisons in this paper. This perspective, adopted by AE companies' welding engineers, forms the basis for a series of review checklists for PQRs and WPSs.

These checklists serve as tools not only for assessing the adherence of PQRs and WPSs to relevant codes and design requirements but also for evaluating the alignment between WPSs and PQRs. Their scope extends beyond ASME BPVC Section IX to encompass other sections of ASME Codes, design requirements, Code Cases, and so forth, pertinent to the construction of nuclear power plants.

These checklists empower AE companies' welding engineers to significantly enhance review efficiency by assessing PQRs and WPSs against these comprehensive benchmarks.

Welding procedure qualifications for weld joints of safety-related SSCs designed per ASME codes are grounded in the ASME BPVC Section IX². This foundation is complemented by specific requirements outlined in other Sections of ASME Codes applicable to the respective SSCs, alongside the design specifications of the specific nuclear power unit (refer to Table 1).

For welding procedure qualification, ASME BPVC Section IX establishes fundamental rules and requirements. It is noteworthy that certain sections of ASME Codes may prescribe requirements differing from those articulated in Section IX, and such specifications take precedence. Additionally, design requirements may surpass those stipulated by ASME Codes.

There are a few basic concepts covered in this article that need to be explained here for ease of understanding.

A WPS is a written qualified welding procedure prepared as a work instruction for the welder. This is the intent of the WPS to provide work instructions to the welder to be able to deposit sound weld metal into a weld joint.

The PQR is the document that supports the WPS. It should be noted that the WPS/PQR relationship is not a one-to-one relationship. Many times, a WPS might be supported by multiple PQRs and the review cycle should have contingency plans for WPSs that are supported by multiple WPSs.

Preliminary welding procedure specification (pWPS):

1. A pWPS is a preliminary document that outlines the proposed welding procedure for a specific welding job or process that will be used to weld a PQR test coupon.

2. It is prepared before the actual welding begins and serves as a starting point for the development of a comprehensive WPS. The pWPS is a work instruction for the welder or welding technician that will be performing the welding on the PQR test coupon.

3. The pWPS may include initial details such as welding process, base material, joint design, welding position, filler metal, and other essential parameters.

4. The pWPS is not a code required document and is as previously stated a document that is used to provide work instructions to the welder performing the initial PQR test coupon.

The workflow pertaining to welding procedure qualification is illustrated in Fig. 1:

1. Technical personnel identify the codes governing welding procedure qualification and the associated requirements from design drawings and technical specifications.

2. Welding engineers develop a pWPS to get their thoughts together on what they will do to weld a test coupon, and then follow those thoughts when welding the test coupon.

3. Test coupons are welded, and then the test process and results are documented to formulate the PQR.

4. Preparation of the WPS aligns with design documents, welding-related codes specified in step 1, and the PQR.

5. WPS is issued for product welding.

According to QW-401 of ASME BPVC Section IX-2007, an essential variable denotes a modification in welding conditions impacting the mechanical properties (excluding notch toughness) of the weldment. This includes changes in the P-Number, welding process, filler metal, electrode, and preheat or postweld heat treatment. A supplementary essential variable signifies a change affecting the notch-toughness properties, such as alterations in the welding process, heat input, and preheat or postweld heat treatment. A nonessential variable signifies a change in a welding condition which will not affect the mechanical properties of a weldment (such as joint design, method of back gouging, or cleaning) [7].

QW-200 of ASME BPVC Section IX-2007 stipulates that a comprehensive PQR must document, at the very least, all essential variables and, when toughness testing of the test coupon is required, supplementary essential variables for each welding process employed in the test coupon welding. Similarly, a fully detailed WPS must address all essential variables, nonessential variables, and, when toughness testing of the test coupon is required, supplementary essential variables for each welding process incorporated into the WPS.

A WPS must address a large number of variables. For example, the WPS for shielded metal-arc welding (SMAW) necessitates 36 variables, as outlined in Table QW-253 of ASME BPVC Section IX, while gas tungsten-arc welding (GTAW) demands 50 variables, as specified in Table QW-256 of ASME BPVC Section IX.

For specific safety-related SSCs, if other sections of ASME Codes or design documents impose additional welding prerequisites for welded joints, these specifications should also be explicitly captured in the PQR and WPS. Special variables, encompassing additional qualification test types and welding conditions mandated by other sections of ASME Codes or design documents, are integral to this consideration. Table 2 delineates the variable types pertinent to welding procedure qualification in nuclear power projects.

The predominant test types and requirements for welding procedure qualification in ASME BPVC Section IX are succinctly outlined in Table 3. When executing welding procedure qualification, welding technicians from manufacturers or construction contractors are tasked with the following responsibilities:

1. Develop a pWPS to ascertain the material, specification, and quantity of the test coupon. Subsequently, compare the variables and test types in Table 2 to ensure alignment with the test requirements.

2. Conduct welding procedure qualification, encompassing test coupon processing, welding, specimen processing, and testing, based on Table 3 and corresponding code provisions. Among them, the key steps/contents include:

3. Qualification testing: The PQR is created based on the results of the mechanical testing that is conducted on a weld test coupon. These mechanical tests are conducted under controlled conditions to ensure that the proposed welding procedure is capable of producing welds of acceptable quality.

4. Welding Variables: The PQR includes detailed information addressing the essential and when required supplementary essential variables used during the qualification tests. These variables may include welding process, welding parameters (such as current, voltage, travel speed), joint details, base material specifications, filler metal specifications, preheat and interpass temperature, and any other relevant parameters.

5. Test Results: The PQR records the results of the qualification tests, including the visual and mechanical testing of the welds. Visual inspection, radiographic testing, ultrasonic testing, and other nondestructive testing methods may be employed, depending on the requirements and industry standards.

6. Acceptance Criteria: The PQR specifies the acceptance criteria for the welds based on applicable codes, standards, or project specifications. These criteria ensure that the welds meet the required quality and structural integrity standards.

7. Document a PQR in accordance with the test process and results, and formulate a WPS based on the PQR, codes, and design documents.

From the perspective of AE companies, reviewing PQRs and WPSs entails distinct considerations compared to the approach taken by manufacturers or construction contractors undertaking welding procedure qualification. Key focal points for AE companies' welding engineers in reviewing PQRs and WPSs include the following:

1. Reviewing the compliance of the welding procedure qualification process and results with codes and design documents. This encompasses aspects such as test coupons, test types, specimens, test procedures, and results. Notably, it is imperative to include weld metal deposited using each set of variables in tension, bend, toughness, and other required test specimens when employing multiple combinations of welding processes, filler metals, and other variables in a test coupon (Sec. 3.2).

2. Assessing the documented essential variables, supplementary variables when required, and/or special variables in the PQR for compliance with codes and design documents (Secs. 3.3 and 3.4).

3. Reviewing the essential variables, nonessential variables, when required, supplementary variables, and/or special variables described in the WPS for compliance with the PQR, codes, and design documents (Secs. 3.3 and 3.4).

The requirements pertaining to welding procedure qualification tests in Articles I, II, and IV of ASME BPVC Section IX are amalgamated to create a comprehensive review checklist for welding procedure qualification test items. Tables 4 and 5 delineate the review items for the widely employed guided-bend test, tensile test, and fillet-weld test.

As illustrated in Table 5, if a PQR specifies that the qualification test employs a single groove weld in a plate with a thickness of 25 mm or less, engineers from AE companies need only verify, with reference to Table 5, whether full-thickness specimens are employed in the tension test. When the test coupon has a thickness greater than 25 mm, multiple specimens of that thickness may be used, followed by one tension test on each set of specimens. Additionally, the two tensile specimens should be processed with a width of 19 mm and a length of 250 mm, or as required, in accordance with Figure QW-462.1(a). Furthermore, the test results should meet or exceed the acceptance criteria outlined in QW-153.

Article I of ASME BPVC Section IX-2007 outlines general requirements for welding, encompassing the criteria for welding procedure qualification such as test coupons, test procedures, and specimens. Article II provides detailed requirements for welding procedure qualification. Tables QW-252 through QW-265 enumerate the specific essential, nonessential and supplementary essential variables in Article IV “Welding Data” that apply to each welding process.

Considering the welding variables procedure specifications for SMAW listed in Table QW-253, the pertinent regulations and requirements from ASME BPVC Section IX Articles I, II, and IV are synthesized and refined to facilitate a more intuitive rule-based comparison of PQR and WPS.

Considering the first two sets of variables, QW-402 and QW-403 in Table QW-253, a total of 10 variables, including QW-402.1, QW-402.4, QW-402.10, QW-402.11, QW-403.5, QW-403.6, QW-403.8, QW-403.9, QW-403.11, and QW-403.13, encompass essential, supplementary, or nonessential variables. Refer to Tables 6 through 9 for a detailed breakdown.

For example, if a groove weld test coupon documented in a PQR has a thickness of 12 mm, and the welded joint has impact toughness requirements, the review entails considering QW-403.6 (supplementary essential variable) for a change in the thickness of the base metal. The lower limit of qualified base metal thickness is 12 mm. Simultaneously, as per QW-403.8 (essential variable), the qualified thickness range of the base metal is 5∼24 mm. Combining these requirements, the thickness range of the qualified base metal in the WPS should not exceed 12–24 mm.

For all other variables in QW-253 and corresponding variables in other welding processes, such as GTAW, gas metal-arc welding, and submerged-arc welding (SAW), review checklists can be established based on the specifications in Tables 6–9.

As illustrated in Table 2, special variables originate from various sources, including other Sections of ASME Codes, design documents, and Code Cases referenced by design documents. A review checklist can be designed to systematically address all special variables.

Considering ASME BPVC Section III Subsection NB, we can examine clause NB-4350, denoted as “special qualification requirements for tube-to-tube sheet welds,” as an example of special variables. In this context, welds necessitate post-weld heat treatment, either according to Table NB-4622.1-1 or granted exemption as per NB-4622.7(b)-1. These stipulations are regarded as special variables [8].

In the case of SSCs, designers may introduce specific welding process requirements derived from engineering practices or outlined in Regulatory Guides issued by the U.S. Nuclear Regulatory Commission. For example, super austenitic stainless-steel welds may demand qualification with the same Uniform Numbering System base material within the seawater cooling system range.

Furthermore, certain Code Cases accepted by RG 1.84, “Design, Fabrication, and Materials Code Case Acceptability, ASME Section III,” may be stipulated in the design document when deemed necessary.

To illustrate, considering material SA-517 Gr.B in Code Case N-71-18, we can formulate a review checklist for elucidation. According to ASME BPVC Section IX, SA-517 Gr.B is categorized as P-No.11B group 4. Code Case N-71-18 consists of Sections 1–6, which entail general requirements or instructions, and Sections 7–15, specifying requirements for different materials. Section 14 specifically outlines requirements for welding S-No.11A, S-No.11B, and S-No.11C materials. Notably, P-No. is equivalent to S-No. per ASME BPVC Section IX [9].

In scenarios where nuclear supports are designed with high strength quenched and tempered material SA-517 Gr.B, and the design document permits welding in accordance with Code Case N-71-18, the welding requirements pertinent to SA-517 Gr.B in Code Case N-71-18 are summarized in Table 10.

Based on the divergent perspectives and focal points inherent in the reviewing process of welding procedure qualification between AE entities and manufacturers/construction contractors, this paper, in line with the methodology outlined in Sec. 3, has translated the stipulations and regulations concerning PQRs and WPSs in ASME BPVC Section IX, other relevant ASME sections, design documents, and Code Cases into explicit descriptions, assessments of correctness, or numerical comparisons. This has culminated in the creation of a series of succinct, direct, and easily used review checklists.

Welding engineers from AE companies, charged with reviewing PQRs and WPSs submitted by manufacturers or construction contractors, utilize the developed review checklists to assess the alignment of these documents with the requirements of the pertinent codes, design documents, and code cases. This evaluation is grounded in a comprehensive understanding of code provisions and design requirements. The result is a noteworthy reduction in the average review time, now shortened to one-fifth of the original duration, thereby significantly enhancing review efficiency.

Concurrently, welding technicians employed by manufacturers or construction contractors can pro-actively employ these review checklists to assess the completeness and accuracy of pWPSs, PQRs, and WPSs. This pro-active approach ensures an elevated quality of welding procedure qualification documents submitted for review.

D =

coupon diameter, mm

T =

coupon thickness, mm

T′ =

base material thickness range qualified, mm

t =

deposited weld metal thickness, mm

t′ =

qualified maximum deposited weld metal thickness, mm

y =

specimen thickness, mm

Acronyms and Abbreviations

AE =

architecture and engineering

ASME =

American Society of Mechanical Engineers

AWS =

American Welding Society

BPVC =

boiler and pressure vessel code

GMAW =

gas metal-arc welding

GTAW =

gas tungsten-arc welding

PQR =

procedure qualification record

pWPS =

preliminary welding procedure specification

RG =

regulatory guide

SAW =

submerged-arc welding

SMAW =

shielded metal-arc welding

SSCs =

structures, systems, and components

UNS =

uniform numbering system

WPS =

welding procedure specification