Hunting for Reliability: Drilling Performance

Courtesy of Hunting Energy Systems

A 20″-dia. oil drilling pin connection is threaded on an Okuma LOC 650 CNC lathe at the Houma, La., facility of Hunting Energy Systems.

Hunting Energy Services not only machines oil and gas drilling components—it assembles and repairs the tools that do the work.

Reliable, affordable energy drives global economic growth. Hunting Energy Services, London, fuels that growth with the products and services it provides to oil and gas producers. For example, it machines drilling components and provides the “mud motors” that extract natural gas from the Marcellus shale gas field in the eastern U.S.

Among the company’s 15 manufacturing operations is its Houma, La., plant, which makes a range of drilling components and accessories and offers finishing services, such as phosphate and copper antigalling thread treatments. However, according to Ron Glanders, manager, technical support, the plant is primarily a “premium” facility that cuts complex, tapered threads for securely joining oil field components.

In addition to cutting threads in Hunting’s proprietary designs, the Houma facility is licensed to machine threads developed by other oil field suppliers. The plant threads components it makes and customer-provided parts.

Hunting’s first priority is product quality, Glanders said. Reliability of drill components is paramount; failure of a single part can produce drilling-rig downtime. Downtime costs can range from $25,000 per day for a shallow-depth, onshore rig to $1 million per day for a deepwater, offshore rig.

As a result, the plant’s processes are tightly controlled, and output is inspected at multiple manufacturing process points. In fact, the first inspection of customer-submitted components occurs when they arrive at the plant, before the Hunting services begin, to confirm the unmachined parts meet tolerances.

For many threaded parts, the plant produces a first-article test piece to check a process’s accuracy. “We will thread a part, take a mold of that thread in rubber, cut out a slice and put it on an optical comparator,” said Paul Matzke, technical coordinator.

Courtesy of Hunting Energy Systems

To thread long pipe sections at the Houma facility, a door (background left) opens to a pipe rack outside the wall of the shop. Hydraulic feed rollers move the pipe through the wall and into the machine tool’s through-spindle, enabling threading of range 2 (up to 34′ long) and some range 3 (up to 45′ long) pipe.

After inspection and approval of the test part, manufacturing of the full production run begins. Production volumes generally are not large. “We may do one or two pieces or as many as 20,” Glanders said. After machining, a part is inspected again before finishing. A final inspection after finishing precedes shipping. “We go through every step to make sure that we are putting out a good product to our customers,” he said.

Inspection techniques vary by component. Some threads are checked with hardened and ground gages, and the threads are physically screwed together to prove their function. Most threads are inspected with calipers or with tapered-thread pitch-diameter gages from Gagemaker’s MRP series.

Going Lean

The plant has established lean manufacturing practices to maximize quality and speed work flow. “A part is in line waiting for the next machine; when it gets to that machine, the operator already has the program, the print and the router, and he’s already been talked to on how to go through the process,” Glanders said.

The Houma facility threads pipes from 1 ” to 20 ” in diameter, with wall thicknesses of about 3⁄8″ to 5⁄8″. Most of the large-diameter pipe is carbon steel, but, especially in smaller diameters, “we machine a lot of nickel alloys like Hastelloy,” Glanders said. The larger pipe is heavy; for example, a 20″-dia. casing weighs from about 94 lbs./ft. to 187 lbs./ft., depending on the material and wall thickness.

To increase large-diameter threading efficiency, the shop acquired an Okuma LOC 650 CNC lathe with 22″-dia. through-spindle chucking capacity. Previously, the shop didn’t have a through-spindle machine that could handle pipe that large. The big parts were threaded on a machine with a plain chuck, and loading and setup were time-consuming.

“We had to put the part on a steady rest; we used to get one thread an hour,” Glanders said. With the large-diameter, through-spindle machine, parts can be loaded quickly, improving production to three threads per hour. The shop primarily uses through-spindle machines, with capacities as small as 7″ in diameter.

The plant’s machine tools are oriented according to the length of pipe being threaded. For shorter parts, the aperture of a through-spindle machine can face into the shop with no concerns about available space. For long parts, however, the shop uses machines that face the wall of the shop. A door opens to a threading rack outside the wall. Long pieces of pipe are rolled from the rack onto a threading table. From there, hydraulic feed rollers move the pipe through the wall and into the machine spindle. When the pipe is positioned on the machine, rotation rollers move under the pipe and the feed rollers move away. The unpowered, free-spinning rotation rollers stabilize the pipe during threading. This arrangement allows the shop to thread range 2 (up to 34′ long) and some range 3 (up to 45′ long) pipe.

Despite the parts’ size and weight, the shop produces precise thread forms. Many of the seals on the threads have a tolerance of ±0.001″ and some tolerances are as tight as ±0.0005″, according to Glanders.

Tool Time

Some threads are machined with multi- tooth threading inserts, but the majority are cut using carbide single-point inserts with ground thread forms. Hunting’s emphasis on quality also shows in its tooling applications. Although the inserts are inspected by their manufacturers, “as we get them, we put them through our own inspection process,” Glanders said.

Chip control in threadmaking is always difficult due to the formation of long stringers instead of discrete, manageable chips. Truly effective chip control technology, Glanders said, “is something we are waiting for someone to invent. People have come up with inserts with chipbreakers and high-pressure coolant, but no one has really come up with a good process to break the chips. So after every threading pass, the stringer must be cleared from the tool; otherwise it could make a bird’s nest and possibly break the insert.”

Courtesy of Hunting Energy Systems

To maximize the reliability of the oil field components it machines, the Houma plant tightly controls processes and output is inspected at multiple points. Here, a pin connection thread is inspected with a tapered-thread pitch-diameter gage.