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Steam valves get overhauled on-site with the help of a boring machine

May 7, 2008
In this installment of What Works, a fast, in situ seat repair relies on a powerful, portable boring machine.

J-S Machine & Valve has been in the valve repair business for more than 25 years. Headquartered in Oklahoma, it has 20 employees and primarily serves the petrochemical and power generation industries in the Midwest and throughout the state of Oklahoma. Nick Hughes, vice president of the company, has responsibility for the field service jobs.

J-S Machine was recently called upon to repair a main steam pressure isolation valve located at a coal-fired power plant in Oklahoma. The plant has two boilers and two turbines, and each boiler has two isolation valves. These valves feature a carbon-steel base with a stainless steel overlay and see 2,500 psi at about 1,100°F. One valve leaked whenever the unit was cold.

Closer inspection revealed that the valve had a high-pressure steam leak caused by seal surfaces that were significantly out of round. The other three valves also were in need of immediate repair to forestall aggressive erosion that could corrode the base metal. A repair would require that the valve seals be re-machined and roundness tolerance kept within 0.003 in. to preserve the seal’s integrity. Not only was the size and depth of the repair unusual – requiring a 14 3/8 in. bore at a 4-in. depth – it also meant that the machinist would be making a blind bore. In addition, the valves were located in hard to access areas.

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Hughes rented the BB5000 Boring Machine manufactured by Climax Portable Machine Tools, Inc. (www.cpmt.com). The BB5000 120-V motor option J-S Machining selected provides 128 ft.lb. of torque in a compact and powerful machine. From past experience with the tool, Hughes found he could use the boring bar not only for valve repair but also to do facing, grooving and threading. The tools’ versatility has allowed him to re-imagine how repairs could be done in the field.

The Climax BB5000 Boring Machine is precise and powerful enough to easily remove 100,000-psi tensile strength material so the isolation valve could be remachined to factory specifications.

The equipment was set up to bore straight down into the blind hole. Hughes developed a sturdy steel base plate for the boring bar by putting the ID mount bearing under the area to be machined to stabilize the bar. He then built a cantilever bearing mount assembly by stacking two double-arm bearing mounts on a tower fixture. The whole assembly was set on top of the valve and bolted to its stud holes, precisely located by sweeping the assembly into location with a dial indicator.

With the 120-V electric motor, the machine easily made a 0.050-in. cut in the 14-inch diameter bore on 100,000-psi tensile strength material to reveal clean base metal, which then was built up by welding so the valve could be re-machined to less than 0.003-in. out-of-roundness factory specifications.

Portability was a critical factor in choosing the BB5000. For this job, the valves’ internal assemblies were removed and carried to the plant floor for re-machining while the valve bodies remained in-line, and as one valve was being welded, another could be machined.

"Ninety percent of the time, when we make repairs, we’re crawling over and through and around catwalks and over pipes," says Hughes. "With some tools you might have to bring them up piece-by-piece by crane or elevator, but the Climax tool is so portable, there’s not one single piece on there that I can’t get up and down the stairs, and it’s easy to assemble and learn how to operate."

Typically, valve repairs of a similar nature only require boring to a 1- or 1 1/2-in. depth and can be done in 12 hours. Because these were 14 3/8-in. valves with a 4-in. bore depth, the boring took approximately 36 hours for each valve, because of the larger area that had to be machined and welded. For J-S Machine & Valve’s customers, though, on-site repair meant savings of 50% to 75% over having to replace the valve or, alternatively, remove it, ship it to and from a machine shop and reinstall it.

After renting the BB5000 for several years and lerarning its capabilities, Hughes finally decided to buy. He said, "The cost savings for me is in owning the equipment because, although Climax can easily overnight the tool, we never know what kind of repair a valve will need until we open it up. Our company has been growing, and we felt we could respond to our customers faster if we had the boring bar on hand."

Hughes is considering purchasing the Climax automatic bore welding attachment in the near future, because he can see its potential in other areas of their work, and the wear and tear it will save his machinists over the manual methods they currently use.

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