Cutting Tool Engineering
March 2011 / Volume 63 / Issue 3

Hunting for Reliability

By Bill Kennedy, Contributing Editor

20 inch pinconnection.tif
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.

At Hunting’s Houma plant, chip control involves juggling multiple factors based on the characteristics of a particular operation. “The major thing is choosing the right chipbreaker, feed rate, rpm and coolant,” Glanders said. “All of those together make a chip break.” There is rarely a simple solution. “If you go in with a faster feed alone, you may be putting too much pressure on the tool,” he said.

The time required to complete a thread is determined by many elements, including thread size, complexity and the workpiece material. For example, a two-step, 2 3⁄8"-dia. TSHP thread can be machined at a rate of six to 10 threads per hour, depending on the operator and workpiece material.

Regarding machine tools, “We try not to put all our eggs in one basket,” Glanders said, noting that the shop generally uses machines from Okuma, Mori Seiki and Mazak. The shop limits the number of machine tool builders it buys from to avoid stockpiling too many different spare parts, he added.

Some of the shop’s CNC turning centers are 4-axis machines. “The machines have a front turret and a back turret that are independent of each other and can do two operations at one time,” Glanders said. “I might be boring and turning, or turning and cutting a seal. We experimented with our first 4-axis machine 7 years ago and we increased production by 30 or 40 percent,” he added.

Quality in the Field

After Hunting machines components for oil and gas drilling, it assembles and applies them in the field. For example, Hunting Energy Services recently opened a drilling products assembly and maintenance facility in Latrobe, Pa., near the center of what is known as the Marcellus shale gas field, which is experiencing rapid development.

According to Michael Arthur, Penn State University professor of geosciences, “The middle Devonian Marcellus Formation in the Appalachian Basin of Pennsylvania and New York is estimated to contain in excess of 486 trillion cu. ft. of extractable natural gas. That is sufficient for more than 20 year’s supply at the United States’ current rate of consumption.”

Hunter Wood II, regional manager at the Hunting Latrobe facility, said the Marcellus formation is “the second largest field of gas in the U.S.”

Courtesy of B. Kennedy

Hunter Wood II, regional manager at the Hunting Energy Systems facility in Latrobe, Pa., discusses the scope of the Marcellus shale gas field, which stretches from West Virginia through Pennsylvania to New York State.

Until recently, extracting the gas has been difficult because of the field’s depth, but advanced drilling technology is enabling producers to cost-efficiently extract it. Tooling like that assembled in Latrobe enables a drill to vertically descend more than a mile, then turn to drill horizontally through the formation.

The drilling tools, called “mud motors,” provide power to a drill bit and enable it to be steered as needed. Located at the bottom of the drill string and attached to the bit, a mud motor is a progressive-cavity, positive-displacement device comprised of a spiral steel rotor that turns within a ridged elastomer (rubber-like compound) stator. The motor is hydraulically driven via a fluid pumped down the drill string from the surface. The fluid, which can be water, mud or even air, turns the rotor and thereby the drill bit.

The redirection from vertical to lateral drilling is achieved using drill string components with a slight bend. When the entire drill string is rotated by equipment at the top of the hole, the bent section produces a hole that is straight and slightly oversize.

But when the drill string itself is not rotating and the mud motor alone powers the bit, the hole follows the bends in the drill string components. A typical mud motor, ranging from 5" to 9 5⁄8" in diameter, is assembled from different combinations of components, producing different performance characteristics.

Some customers choose to purchase the tools from Hunting, but usually the tools are rented. Hunting tools are recognized as premier motors that perform as expected under harsh operating conditions, Wood said.

The facility’s work begins when a drilling contractor contacts it to obtain a mud motor of a specific size and performance capability. The shop assembles the motor and sends it to the drilling contractor, who runs it for a specified period, after which the motor is returned to the Latrobe facility where it is disassembled and the parts are cleaned and inspected. Components are evaluated based on several quality criteria, such as cracks, metal and rubber fatigue, chrome pitting and thread functionality. If parts are out of conformance, they are disposed of, repaired or replaced out of inventory. The motor is then rebuilt.

The facility’s field sales representatives focus on customer service and are the front line between drillers and the shop. Responsive service and top-quality tools are crucial. “If you are 7,000' underground and that tool breaks, then you’ve got to fish all those tools out,” Wood said. “That rig runs 24/7, and downtime is costly.”

The shop cleans mud motor components in two parts washers: a smaller unit that can handle parts up to about 5' in length and one for components up to 30' long. The large washer is a one-off, first-of-its-kind unit that forces a mixture of preheated water and soap through the center of a pipe to remove grease and mud. The self-contained system is environmentally compliant, as are all waste products from cleaning components in the facility.

If threads have burrs or are scarred, the shop cleans them on an Okuma CNC turning center with a through-spindle chuck. After chasing the thread with an appropriate insert form and shot-blasting the tool to clean it, the threaded tool is dipped into a phosphate solution to prevent rust.

Hunting’s Latrobe facility is gradually ramping up to full capacity, at which point it is expected to process 20 to 30 tools per week. To track the large volume of tool components and replacement part inventory, the shop is investigating the use of a 2-D, dot shot-peened bar coding system to enhance traceability and vendor part history tracking, and also determine hours to failure.

Courtesy of Hunting Energy Systems

In this area of the Latrobe plant, mud motors are disassembled before inspection and reassembled before being returned to the field.

The permanent markings the system produces can survive the drilling environment. Laser engraving is a possible alternative marking method, but it is more expensive, and the laser can heat the part and affect metal integrity.

Makers of advanced drilling tooling such as Hunting Energy Services play a key role in assuring that the world’s supply of natural gas is truly reliable and cost-efficient. CTE

About the Author: Bill Kennedy, based in Latrobe, Pa., is contributing editor for CTE. He has an extensive background as a technical writer. Contact him at (724) 537-6182 or by e-mail at
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