Oil Field Goods
Workpieces may be slippery, odd-shaped, and large or long turbular pipe and bar
Oil prices are widely expected to remain above $100 a barrel throughout the year well above the rule-of-thumb level of $60–70-a-barrel that makes economic sense to aggressively pursue domestic drilling. In combination with extensive activity for the natural gas extraction method of hydrofracking (a.k.a. fracking), there’s enough drilling activity to ensure that shops will have a ready market for their machining capacity for oil field goods. The increased activity, especially as it expands the geographic activity to the north and northeast to the natural-gas bearing shale formation states, is offering increased business opportunity for machine shops located nearby and for machine builders and distributors and their third-party suppliers of tooling and workholding.
Workholding solutions for the oil and gas industry constantly are challenged by materials, the size and shape of workpieces, and the processes being performed, which include but are not limited to turning, milling, grinding, and honing. Oil field goods include products ranging from tubular goods for casings and the drill string, wellhead valves, and accessories like chokes and mandrels that are needed to drill and complete wells. Workpieces range from unwieldy tubular pipe in varying sizes, typically in 30' (9-m) lengths, to solid slippery bar that must be held securely without interfering clamping. Pipe wall thicknesses can range to 1" (25 mm) required to withstand higher pressures in deep wells or be thin-walled and difficult to hold.
Large, awkward-to-handle, odd-shaped workpieces are common in the oil and gas industry. Just picture the Christmas tree valves and manifolds that start out as forgings, castings, or large blocks of steel and you’ll get a feel for the diversity of such workholding challenges. Turning these parts due to their unbalanced odd shapes was a specific development objective for Mazak Corp.’s (Florence, KY) Orbitec 20 valve body production center. In creating a machine that generates turned feature by moving only the cutting tool while the workpiece remains stationary, Mazak has also created a unique workholding solution for this category of workpiece, and any others that exhibit similar physical characteristics.
Avoiding Out-of-Balance Conditions
When these types of large odd-shaped parts rotate around a stationary tool, out-of-balance conditions can arise due to their masses and often lopsided shapes. The ideal way to generate turned features on big cumbersome parts, Mazak reasoned, is to do so while the parts remain clamped and stationary, moving only the cutting tool. The Orbitec 20 is able to complete most valve and other large-part machining in one clamping, with the ability to generate phonographic finishes on flange surfaces, tapered bores, and perform feed-out grooving operations. In addition, other processes, including trepanning, internal grooving, and concave machining, are possible. The Orbitec 20 features a dual 630-mm pallet changer that matches the pallet size of the HCN 6800 machining center and is compatible with Mazak’s Palletech system so that a complete automated valve production machining system can be configured.
Automated machining of couplings, which can be produced by both vertical and horizontal turning centers, requires careful attention to chip control. “Materials used for oil and gas drilling must operate under difficult conditions deep underground or undersea,” says Jeff Estes, director of Partners In THINC (Charlotte, NC). “When machined, they typically produce chips that tend to become long and stringy. The challenge is to break chips into manageable sizes so that chip flow is controlled thus making it easy to evacuate them without stopping the machine. Without good chip breakage, the stringy chips tend to gather on tooling and workholding making it virtually impossible to automate this machining process .”
“We have automated both processes in the Okuma Oil Coupling Cell to keep spindle utilization high. With an automated system, there isn’t an operator needed to remove the chips. Robots can handle couplings that weigh as much as 70–120 lb (32–55 kg) and be from 3 to 19" (76–482 mm) in diameter with sufficient wall thickness to withstand the weight of pipe and pressures of oil,” says Estes. One version of the Okuma Oil Coupling Cell combines two CNC machines, a VTL and an horizontal turning center. The coupling cells are complete packages that can be customized with a variety of machine configurations to meet specific customer needs. Each is set up and ready to run with special workholding, chip evacuation, cutting tools, and programming. Special attention has been paid to chip evacuation, because of the potential volume of long stringy chips that are produced in turning and especially threading.
Many Ways to Hold Workpieces
Oil field workholding products available from Schunk Inc. (Morrisville, NC) include lathe chucks and chuck jaws, stationary workholding, and magnetic workholding. “We focus on getting more parts to the spindle that will allow the users to get as much production as possible out of their machines,” explains Brad Evans, product manager-workholding. “In addition to workholding for rotating solutions we offer workholding for turning nonround parts like pump housings with special chucks or the Vero-S quick-change palleting systems for horizontal turning on VTLs. Stationary workholding includes complete stationary workholding such as pneumatic, hydraulic, and manual products, and a complete line of magnetic workholding.”
Schunk’s Vero-S quick-change zero-point pallet system is designed to allow change out of a machine in a matter of minutes and increase the capacity of the table, because the fixture clamps are on the bottom of a pallet or workpiece. “With the clamping pin inserted into the bottom of a pallet or a workpiece, we achieve 5µm repeatability in moving from machine to machine, as long as both are set up with the Vero-S,” says Evans. “All that has to be changed over are tools and program. This also works for a CMM. A part can be cut on a machine, left on a fixture, taken to the CMM on the fixture, inspected, and returned to the machine for rework if necessary in minutes without a time consuming locating process.”
The Vero-S concept allows the user to set up a machine quickly, reduce spindle downtime, and maintain accuracy and rigidity. “When machines are sitting idle, they’re losing money. Vero S is designed for milling, grinding, broaching, finishing, and turning. It establishes the zero point for the machine. The entire unit is made out of hardened stainless steel and fully sealed. These two improvements have virtually eliminated the possibility of corrosion, and binding”.
“For larger applications, we can monitor the clamping slides. You can imagine that you have a machine with a 20' [6-m] bed and a fixture up there weighing several tons, if you had a pin that was stuck in the older version, you didn’t know that, and you tried to pull this 5-t fixture off, that’s a problem. The new system monitors the slides through air switching and an alert. With stainless construction, it’s almost unnecessary, but it does represent peace of mind for the machine operator,” Evans says.
Schunk’s magnetic workholding includes permanent electro milling magnets, grinding magnets, and radial turning magnets from 8" (203-mm) to 4-m diam. “Magnetic workholding has proven to be especially effective in large prismatic parts or round parts,” says Evans. “With magnetics, for example, we can hold bar stock 10” (254 mm) in diam up to 7-m long (or longer) or fixture prismatic workpieces like housings or blout preventers on five-axis mills so that five faces can be accessed for machining. This reduces setups and improves accuracy.”
Constant State of Improvement
“Workholding solutions for the oil and gas industry are in a constant state of improvement,” says Larry Robbins, vice president-sales, SMW Autoblok Corp. (Wheeling, IL). “It’s getting more and more competitive to pull oil out of the ground in North America, and we’ve developed the technologies that allow it to be done at a lower cost and allow us to do more onshore production of oil and gas.” SMW Autoblok’s Oil Country Tubular Goods guide includes everything from its simple standard trademarked Big Bore through hole front-mounted pneumatic chuck to the latest self-centering, compensating chucks. “Putting pneumatic chucks on both the front and rear of the machine spindle, replacing a manual chuck, overcame the problem of the pipe whipping around wildly,” says Robbins. Extended stroke versions of chucks allowed pipe with flanges to clear the jaws of the chuck as it was pushed through as processes are changed or new pipe is loaded.
Pipe is presented in one of several different ways to the machine. It comes in straight or bent due to out-of-round condition of the pipe or due to natural sag of long pipe. Using a standard air chuck requires shimming the jaws to accommodate the out-of-round condition. To address these conditions, SMW Autoblok introduced its BIG Bore BB-AZ three-jaw chuck which allows operating the chuck in either the self-centering or compensating mode. “The BB-AZ chucks can do one or the other, but can’t do both at the same time. They do save an operation by centering the pipe or clamping it in a compensating mode and doing away with the need to shim the jaws.”
for the oil and gas industry are in a constant state
To speed clamping, SMW introduced the BB-SC three-jaw chuck clamping with spring packs, which also allows partial opening and closing (jogging) for shimming. With spring close and air open, the chuck reduces standard air chuck opening from 12-15 sec to 3 sec and offers constant and consistent grip force, saving time and power needed for shop air. “The Spring Pack Chuck does away with the need for air to close so you’ve cut your consumption at least in half and you’ve cut the time way back because the spring to close only takes milliseconds to actuate to close on the pipe” says Robbins.
“Our newest technology is the BB-FZA self-centering and compensating chuck--all built into one. With it you don’t need a centering chuck to centralize the part, and basically it allows you to grab a piece of pipe whether it’s bent, out-of-round, or deformed. If you’re threading a piece of pipe, it centralizes the pipe with three jaws, once the chuck sends feedback through its PLC to the CNC control, it allows you to centralize to the bore of the pipe with the center along the spindle of the machine. The compensating jaws come in and clamp on the OD of the part and adjust to the part with swivel or roller jaws. Once the centering jaws sense that the compensating jaws are clamped in a position, they retract. You’ve cut a whole operation out of what used to take to centralize a piece of material with a centering chuck, shim the jaws, clamp the part, and every time you re-clamped your piece you had to go through all these operations over and over again. “We’ve cut, depending on the application, up to 50% out of the processing of each piece of pipe.”
Good Times in the Oil Patch
These are good times for the oil industry, says BJ Lillibridge, Pratt Burnerd America/Atlas Workholding (Kalamazoo, MI). “Business is at a high level and the principal challenge is capacity, keeping up with the growth of the industry. We’ve seen oil industry cycle many times over. It’ll go from not being able to keep enough product in supply to having inventory nobody wants. Our oil country chucks, the King Bore Oil Country three-jaw universal manual chucks come in sizes from 20" up to 48" [500 mm up to 1200-mm] diameter and larger if needed. But the most popular sizes in the industry are 24 and 32" [600 and 800-mm] diameter.”
Two different styles of chuck are available. “One is the four-jaw independent chuck with each jaw moving independently so you have full adjustment for concentricity. They are used on the front and on the back of the machine. The other style is a three-jaw chuck with universal design. All three jaws go in and out simultaneously so there is no special concentricity adjustment. Four jaw chucks which is the oldest technology outsells three jaw chucks by four to one. For big bore lathes, manual chucks feature through holes from 6.5 to 21" [165–533 mm]. “Our chucks swallow the pipe and hold it securely with special diamond-shaped gripping serrations, because when the threading is being done, the pipe is slippery and takes a lot of jaw force to grip it,” says BJ Lillibridge. “One thing we have noticed recently is that some of the machine builders have decreased the through hole on the machine to increase the rpms, but that doesn’t pose any special problem.”
”Sometimes, a large
can be solved with a little out-of-the-box thinking.”
Sometimes, a large workholding problem can be solved with a little out-of-the-box thinking. Gerard Vacio, product manager-workholding, BIG Kaiser Precision Tooling Inc. (Hoffman Estates, IL) offers this solution to just such a problem about holding very large workpieces. “Whenever I am asked to offer workholding solutions for very large work, I consider flipping the tool and not the work. The time required to unclamp a large part and use a crane to flip it can be extensive. Flipping the tool with an angle head might be more cost-effective. Form and positional tolerances can also improve when multiple faces of a large workpiece are machined in one setup. The workholding task might be to design a methodology to hold large parts without obstructing access to features on multiple faces. Five-sided access would be best so you have the option of either flipping the entire workpiece on a zero-point fixture plate, or using an angle head.”
Vacio continues, “BIG Kaiser can address the five-sided access issue with Unilock, our zero-point clamping system, which uses ground retention knobs on the back side of the fixture plate or workpiece to pull it down onto the top of the table equipped with Unilock pneumatic clamping chucks and lock it into an accurate location. The entire assembly can then be flipped into new orientations for subsequent operations, or an angle head can be used on as many operations as possible in the original setup.
“Also, pulling a part down is better than squeezing it. The squeezing process puts stress on the raw material and the material removal process can compound the negative effects of this stress. Pulling the workpiece down from one side allows the material to sit in a free state for machining. However, walls may need to be supported to control harmonics that would normally be damped by the squeezing process,” Vacio concludes. ME
This article was first published in the February 2012 edition of Manufactuing Engineering magazine. Click here for PDF.