Mobile Navigation

Critical welding

For critical welding applications, thorough and detailed documentation is required

Critical welding requires critical documentation. There are engineering applications where weld failure is not an option without placing undue risk on human life, the environment or property. For these critical applications, detailed documentation is required to provide welding personnel the requisite information to successfully weld a weld joint. Some of the companies that understand this philosophy the most are those engaged in American Society of Mechanical Engineers (ASME) Section III nuclear component fabrication/repair, ASME Section VIII pressure vessel fabrication/repair, or seismic structural engineering or oilfield pipe fabrication/repair applications.

Without such documentation, weld nondestructive examination/nondestructive testing (NDE/NDT) failure increases in probability, weld joint safety margins are compromised, design service life expectancy is lessened and performance of the weld joint is degraded.

Key documents employed by welding personnel throughout production welding include the welding procedure specification (WPS) and the operational instruction (OI). Per AWS A3.0 Standard Welding Terms and Definitions, a WPS is “a document providing the required welding variables for a specific application to assure repeatability by properly trained welders and welding operators.” An OI complements the WPS by providing a step-by-step checklist of instructions and additional information required for welding.

The procedure

A WPS is employed by a company to govern welding throughout the tenure of a production contract. A code WPS is in accordance with a code-qualified procedure qualification record (PQR). A PQR is a welding engineering document whereby a test coupon comprising the same base/weld metals of the proposed weldment is subjected to testing to determine if the weldment is capable of meeting the intended service application. A PQR contains the test results of the tested coupon. Testing of a PQR coupon may comprise:

• Mechanical testing (e.g., tensile, guided bend, drop weight, crack tip opening displacement [CTOD], Charpy V-notch, etc.)
• Chemical analysis testing (e.g., weld deposit analysis, etc.)
• Metallurgical and metallographic analysis (e.g., intergranular corrosion, intergranular fracturing, etc.)
• Service environmental testing (e.g., temperature, chemical exposure, etc.)
• NDE/NDT inspection

For production welding, personnel use the WPS and not the PQR. The WPS cannot be written without first qualifying a PQR. In which case, the variables documented within the WPS are based upon the actual variables developed during the welding of the PQR coupon. Therefore, to repeat the test results of a qualified PQR, it is pivotal that the WPS be accurately written and that all variables documented within the WPS (i.e., essential, supplementary, nonessential) are strictly adhered to throughout production.

Follow instructions

Due to the complexities and demands of certain welding applications, an OI is employed. An OI is a comprehensive document that complements the WPS by providing a checklist as well as pertinent and vital information to further support welding efforts. The checklist provides step-by-step instructions detailing each required operation to be performed in sequential order to facilitate achieving high-integrity, first-time quality welds.

The objective of an OI is to provide clear, well-defined instructions and information to be employed for respective applications (e.g., onshore/offshore oil & gas fabrication/repair work, nuclear power plant outage work, etc.). It is the responsibility of welding personnel to follow the OI word for word.

An OI will include welding equipment requirements, weld variable information, heat input per weld bead, NDE/NDT inspection criteria, post-weld heat-treatment criteria, power supply program settings, weld joint geometry details, any special in-situ machining/tooling requirements, weld bead sequence map, tungsten electrode tip geometry, etc. An OI is application specific and proprietary to the company.

The three-page, ASME-IX:2019 Code qualified WPS for P-No. 1 material (carbon manganese or low-carbon steel). The example illustrates the detail involved with creating a WPS.

Regardless of the weld code being employed, such as ASME and AWS, in the writing of the WPS or OI, it is important that all variables – essential, supplementary, nonessential – be listed. It is crucial as well that all relevant information be available within an OI so welding personnel have no questions or lingering doubts about how or when each operation is to be performed.

Welding personnel must be properly trained in the implementation and utilization of critical documentation (e.g., classroom instruction, weld mockups, etc.) and have confidence in the information being presented. In certain cases, welds are being conducted on a one-of-a kind basis or, with a new design, on a first-of-a-kind basis. Therefore, there cannot be any confusion, misinterpretations or misunderstandings. Throughout production, welding personnel rely on the integrity of the WPS and OI documents for accuracy, reliability, consistency and validity.

William C. LaPlante

Comments

Comments powered by Disqus.