Repairing steam turbines is all about efficiency, quality, and precision. Customers in the petrochemical, oil and gas, and power-generation businesses may be losing hundreds of thousands of dollars a day if a key piece of turbomachinery is down. And, for equipment that may weigh several tons, rotate at high speeds, and run at high temperatures, quality is an absolute requirement.
To add to the challenge, there are almost never original drawings to go by, at least not for independent repair companies such as Hickham Industries (La Porte, TX). A unit of Sulzer Turbomachinery Services, Hickham claims to be the largest and most diverse such facility in North America.More often than not, drawings have been lost over the years. Even when available, they may not be very helpful. Because of modifications made during manufacturing, no two pieces of turbomachinery are ever exactly the same-even if they have identical model numbers. Problems are multiplied by the effects of wear and corrosion; overheating and crashes that leave key components bent, cracked, or broken; and multiple rebuilds.
In light of these challenges, Hickham personnel have become experts in reverse engineering. Work at La Porte always starts with careful measurement using portable coordinate measurement machines (CMMs) to establish nominal dimensions.
"The first step is to establish what we have, where we are, what we know and do not know, and what we have to do," project engineer Jaime Valdez explains. "For that, the portable arms are essential."
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Hickham has conventional CMMs, but most of the machinery it refurbishes is too big to be dimensioned anywhere but out on the shop floor. For that task, the company uses portable arm CMMs from Romer/ CimCore (Farmington Hills, MI). Hickham purchased four of the company's 3000i arms in early 2002-three with a 9' (2.7-m) measuring envelope, and one with a 12' (3.7-m) envelope. Hickham is now looking at adding accessories such as Romer's Linear Rail and GridLok systems to further expand measuring envelope and versatility.
"These are close-tolerance, high-speed, high-horsepower, high-temperature machines that generate high revenues for our clients," explains project manager Dave Dixon. "With equipment like this, the margin for any type of error is very small and the price of an error is extremely high. The Romer arm is one of Hickham's key tools to verify our efforts in maximizing the machine's output and minimizing the chance for error."
The portable arms are used to measure casings, shafts, shaft supports, disks, diaphragms, and bladed turbine rotors, plus impellers for centrifugal compressors. "Data from our reverse engineering efforts supports all the key decisions on what repairs are needed, how they will be done, how long it will take, and which parts must be replaced," Valdez explains. "Also very important is getting measurements quickly."
Speed is a factor in Hickham's success. Turbomachinery repair is a competitive business, and jobs are taken on fixed-price bids with demanding delivery times. "On one rush job, we had just 27 days to disassemble the entire turbine, dimension it, weld the case and repair cracks, fix the rotors, repair a lot of the blades, and fix the stationary parts," Valdez recalls.
"With the portable CMMs we can get axial and linear measurements-bearing areas, rings, stators, and vanes-all at the same time with just a few quick changes in the setups," explains operator Jesse Haver. "We do it all with just one man rather than two or even three. It will take eight man-hours rather than 32."
According to Haver, the device's reverse engineering software aids data collection. "One thing about the arm's software, PowerInspect, is the ease with which reference planes can be changed even after points have been gathered," he points out. "Often, we need to be able to relocate geometry planes and move points between them. With PowerInspect, there's no need to go back and remeasure. We know the data was good." All dimensional measurements are checked at least three times by Hickham personnel in various departments, he adds.
Accurate measurements made with the portable CMMs mean Hickham machinists no longer do trial-and-error machining.
Surfaces measured range from simple flats and arcs to volute surfaces of centrifugal pump impellers. "Our machinists then cut these parts to our numbers," Haver says. "The accurate measurements mean they no longer have to do trial-and-error machining. We can now do in two days what sometimes took weeks."
Rotating stages of turbines are often up to 52'' (1.3 m) diam, and the full assemblies may be 35' (10.7 m) long. "But, we are often working in confined spaces, and the arm's almost unlimited rotation is a big help," Valdez says. "It always takes a while to get the measuring setup oriented and maneuvered into just the right position and locked down.
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