Pipe and tube welding products exist in service in a variety of forms, from simple, straightforward strings of piping to large, complex systems with joined components.
Pipe and tube welding products exist in service in a variety of forms, from simple, straightforward strings of piping to large, complex systems with joined components.
They are produced from a broad spectrum of materials, from mundane carbon steel to very advanced alloy combinations, and serve as essential infrastructure for transporting, containing, and supporting products and materials in all kinds of environments and industries. The methods, materials, and choices made to join these components are equally diverse.
Riley Power Group (RPG), a field welding, machining, and specialty staffing company, reminds us that “good fit-up and the proper end prep are often the most important keys to a successful weld.” Those priorities are certainly fundamental to quality, simplification, and repeatability; however, a longer list of other considerations can be just as important.
It would be too lengthy to address every aspect of material supply, welding process optimization, and welder attributes in this article. Instead, what follows are a few considerations and places to go for help as resources and knowledge continue to diminish through shrinkage in the supply chain, retirement, and changes in our culture.
Field Heat Treatment
One principal consideration in many applications is the need for field heat treatment. It is essential, in many cases, to good weld quality, fitness for service, and, ultimately, return on investment. Prevention of solidification cracking, diffusion of hydrogen and other harmful constituents that are common failure mechanisms, phase transformation, curing, and annealing are some reasons to heat treat. AWS D10.10/D10.10M:2021, Recommended Practices for Local Heating of Welds in Piping and Tubing, and D10.22/D10.22M:2021, Specification for Local Heating of Welds in Creep Strength-Enhanced Ferritic Steels in Piping and Tubing Using Electric Resistance Heating, provide guidance for properly heating a specimen, regardless of heat source (electrical resistance, induction, furnace, or combustion).
Typical welding schedule with associated heat treatment processing based off Fig. 6.4 from AWS D10.10M:2021.
For years, this area of specialization has been greatly underappreciated and overlooked in its contribution to successful welding and material processing. As advanced alloys become more prevalent, their dependency on uniform, controlled heat treatment is more important than ever. It has been estimated that 90% of weld failures and anomalies in these alloys can be traced to improper heat treatment rather than mistakes from the welder themselves. This has driven industry to invest heavily into research and studies that have led to many of the revisions and updates to codes and standards we see today. In most cases, these changes were helpful, but they also add complexity that requires higher levels of competence, integrity, and attention to detail in pricing, asset allocation, control, and monitoring practices.
Inspection and NDE
Safety and quality are important factors in this industry. Lots of exciting new tools and improved techniques are being introduced into field inspection services, nondestructive examination (NDE), and quality assurance programs. They significantly enhance safety, performance, and record keeping and minimize risk as part of overall operations and life management strategies. For example, two effective NDE methods to verify proper heat treatment are surface hardness testing and taking replications.
In many cases, heat treatment providers are contracted to provide hardness testing themselves to validate the effectiveness of the process. By its nature, heat treatment is virtually impossible to declare a success through a visual examination alone. Even hardness testing has its shortcomings depending on the technician training and what the inspector is most interested in validating. The tools themselves are subject to variability from factors such as surface prep and the location where the measurement is taken. Terry Haigler, general manager and researcher at Applied Inspection Systems’ Advanced Technology Center, explained that hardness readings are generally taken from multiple locations around the circumference of a pipe, noting results in the weld metal, heat-affected zone (HAZ), and base material.
Field heat treatment pipeline testing. (Photo courtesy of Legacy Heat Treatment and Republic Testing Labs.)
Surface replications, or cutaways, can be performed after postweld heat treatment (PWHT) to evaluate actual grain structure to ensure the proper material transformation has occurred. Replications provide more information about the actual condition of the HAZ when the desired microstructure is known. Other inspection techniques might also be effective, depending on what the inspector is looking for.
Magnetic particle inspection (MT) can provide confirmation that no surface cracks are present. Improper heat treatment could cause the material to crack if the heat treatment ramp rate was too fast or it was cooled too quickly. Phased array ultrasonic inspection is a more advanced technique than MT in the sense that it will tell the inspector if cracking has occurred due to incorrect heat treatment parameters or if any welding defects like slag or incomplete fusion caused cracking during proper or improper PWHT.
The reader is encouraged to investigate advances in pulsed eddy current, advanced ultrasonics, and multifrequency microwave technology as well as emerging modeling tools utilizing powerful, simplified, affordable software for collecting data, simulations, predictive analytics, record keeping, and reporting from industry experts like Haigler.
Conclusion
Piping and tubing systems are critical components in so many of our industrial operations and processes. The complexity and variability compel conscientious industry professionals and companies to invest in continuing education and networking with experts in the field to ensure safe, efficient, reliable service and remain competitive in a rapidly changing marketplace. Readers are encouraged to attend local AWS Section meetings in their areas and, if possible, plan to attend the upcoming three-day Welding Summit 2023 (aws.org/weldingsummit) at The Woodlands Resort in The Woodlands, Tex., August 16–18.
This article was written by Gary Lewis (president of Lewis Reliability Resources, Mooresville, N.C.) for the American Welding Society.
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