By GARY LEWIS, director of Business Development, SuperheatFGH Services, Inc. Edited by RICHARD MANDEL, senior editor

With post-weld heat treatment equipment in place and standing by, a welder joins two segments of pipe.

The push to increase oil production in Northern Alberta's tar sands has affected businesses up and down the supply chain, including the Canadian construction and infrastructure development company, Aecon Group, Inc. (www.aecon.com). The company's western operation is at the Alberta-based epicenter of the booming oil and gas business in western Canada, for which an estimated $100 billion Canadian ($86.4 billion US) investment in plants and equipment will be made over the next decade.

Aecon operations include pipe fabrication, refinery module assembly and site construction services. Heat treatment processes are required in all three divisions, particularly where there is need for stress relief of alloy steel components and piping.

"An important activity that we perform for clients, whether we're fabricating pipe, assembling modules, or working on-site, is welding," said Diego Carducci, the construction operations manager for Aecon's western operation. "When it comes to pipe and components fabricated from chromium-molybdenumvanadium (9CrMoV) alloyed steels, such as P91 and P92 grades (commonly known as ‘chrome' or ‘chrome steels'), or heavier thickness carbon steels, heat treatment is mandatory. Codes specify the heat treatment cycles during and after welding to yield the proper post-weld strength and ductility and to markedly reduce the chance of weld cracking."

Welds on refinery projects are required by Canadian government authorities to receive proper heat treatment. In performing a welded joint for chrome, for example, the material has to be stress-relieved after welding using non-destructive testing procedures. Weld hardness is checked using either Brinnell or Vickers scales, and final post-weld hardness must be certified within a certain range, depending on the welding procedure.

Rebuilding a distiller
In 2005, Aecon began the rebuild of a distillation (or fractionation) tower for Suncor, a Canadian company that is mining the oil sands in northern Alberta to produce synthetic crude oil. Such a tower is used to separate the different grades of crude oil during the refining process.

The project ran for three months and involved demolishing piping, tearing down the vessel, replacing piping, and repairing and reinstalling the vessel. The job also required a plant maintenance shutdown to take care of systems and equipment needing repair.

"It was a fairly intense schedule," said Carducci. "The tower had to be rebuilt in eight months, a task usually taking at least twice as long. We were working seven days a week, 24 hours a day."

Both the rebuild and the maintenance required a significant amount of heat treatment. The 4-in. dia., ³/₈-in. wall thickness alloy steel pipe, which varied from 2.5 percent to 9 percent chrome, was selected by the project's engineers and consultants to achieve increased service life and operating pressures. Aecon worked with SuperheatFGH Canada, Inc. (www.superheatfgh.com), which supplied a Super 6Wi heat treatment system that operates with a wireless process control.

When it comes to heat treatment, Carducci said that the heat cannot simply be turned on and then turned off. The process must be very controlled with regard to the manner in which heat is stepped up, held and stepped down. Welding codes usually mandate precise temperature, time, heating, and cooling cycles, depending on the alloy and service requirements, because post-weld heat treatment affects mechanical properties. To assure compliance and accuracy, the Super 6Wi automatically checks the actual temperature at each joint and compares the reading to the required temperature. All data is duly recorded for the quality assurance package that Aecon turns over for Suncor for weld process documentation.

"Because of the nature of the process and the amount of control required, at first I was doubtful as to whether a wireless solution would actually work in a rough industrial environment," said Carducci. "As we progressed and the temperature data came in, everything was documented and accepted by our client."

Reducing manpower
Wireless control of the heat treatment process allows centralized data gathering. As a result, one person can monitor many more weld joints more efficiently.

"If the heat treatment had been done traditionally, it would have taken many more people to monitor the process," said Carducci. "The hard part of a post-weld heat treatment is monitoring actual temperatures and making sure that you have the proper temperature-time profiles in terms of how you raise, hold, and lower the temperature — monitoring makes or breaks the whole process."

Fewer people at the site passively watching chart recorders means a smaller crew who can work more effectively and at less cost. Ralph Falle, the local superintendent of operations for SuperheatFGH, said that day and night manpower needed for the project consisted of 9 technicians in the field setting up the heating elements on-site, two technicians monitoring two HT units locally, and one technician in the control room.

"This same job with this much equipment would probably take a traditional heat-treatment company an additional six technicians to monitor chart recorders," said Falle, calculating the cost savings of using wireless heat treatment on this project at around 23 percent less than traditional technology. "With even newer technology now in place that further centralizes monitoring capabilities and reduces manpower, additional savings would likely add up to an additional 5 percent or so, for a total of 28 percent savings over traditional heat treatment."

To further illustrate cost savings through the use of a wireless system, Falle recalled recent involvement with another client's annual maintenance shutdown, whose policy was to produce contractor purchase orders based on historical costs.

"P.O.s for us came to about $1.2 million, based on traditional technology. At the project's end, the cost to the client using wireless technology came to $820,000. This represented a 34 percent cost savings to the client, or approximately $420,000," said Falle. "We don't have nonproductive people. We can transfer data wirelessly from various machines to one remote location, which permits productive manpower to go to a specific job location, wrap up that work piece, and move on to the next location to perform other duties. No one stands still."

"The effectiveness of the wireless heat treatment system was spectacular in terms of control, and much more effective than a manual control system," said Carducci. "With the number of activities going on at this project, the method of heat-treating chrome pipe never came across my desk as an issue — which from a project manager's point of view, is a very good thing."

Heat treatment and CrMoV alloy steels The past few years have witnessed the rapid introduction of 9 percent chromium-molybdenum-vanadium high-strength alloy steels, such as P91 and P22 grades, both of which retain their strength at elevated temperatures and possessing good fabrication characteristics. These steels have become the material of choice within the power generation industry for high-temperature steam and other, similar non-corrosive service — according to W.F. Newell, P.E., vice president of Euroweld Ltd. (www.euroweld.com), a dramatic increase in the specification of P91 has occurred for applications such as main steam lines and heat recovery generators. However, these alloys achieve their strength and hardness as a result of the austenite-to-martensite transformation, which occurs during rapid cooling from elevated temperatures. If this transformation were not controlled, excessively hard and brittle properties would result, with the consequent risk of weld cracking either or both after welding or in-service. Both are obviously unacceptable. Since such temperatures are unavoidable during welding, the cooling rates experienced in the heat-affected zone during welding must be controlled. Codes specify required preheat, interpass and post-weld heat treatment temperature cycles to assure that the optimum metallurgical changes occur during the weld heating-and-cooling cycles.