Innovative Fastener Handles Shock, Heat, and Vibration of Oil Industry Drilling Equipment
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Innovative Fastener Handles Shock, Heat, and Vibration of Oil Industry Drilling Equipment
A unique internal thread form is helping the oil industry enhance reliability even in super alloys by combating vibration, thread loosening, and extreme temperature, while easing assembly, maintenance and inventory management without need for secondary locking features.
Whether drilling or producing, oil rig operations have some of the harshest operational requirements of any industry. That’s particularly true today as more remote, hard-to-reach onshore and offshore oil reserves are sought, and the demand to drill deeper at higher speed continues unabated. Despite ever more extreme shock, vibration and temperature, critical joints must be maintained and production downtime minimized.
From drill collars, cutting tools, and high pressure valves to down hole tooling for controls, measuring and monitoring, the tapped holes and fasteners holding vital equipment together must operate with virtual 100% reliability-because the cost of failure or unscheduled service when a million-dollar component is thousands of feet below ground or sea level can be astronomically high. To maximize safety and production uptime, fastened joints must stay secure with minimal maintenance, particularly in the well bore.
While many engineers gravitate toward lock wires, prevailing torque fasteners, or adhesives to prevent loosening, these may be less effective in oil rig applications or have higher total cost when maintenance and production issues are considered.
As an effective alternative to traditional fastening methods, a unique internal thread form is helping the oil industry enhance reliability by combating shock, vibration, thread loosening, and extreme temperature even in hard-to-cut super alloy materials, while easing assembly, maintenance and inventory management.
Solving Fastening Problems with an Innovative Thread Design
Most locking fasteners do not address a basic design problem with the standard 60-degree thread form: that the gap between the crest of the male and female threads can lead to vibration-induced thread loosening. Stress concentration and fatigue risk at the first few engaged threads is also a problem. Temperature extremes can also expand or contract surfaces and materials, potentially compromising joint integrity.
Engineers, however, have successfully attacked these challenges while easing assembly, maintenance and inventory management with innovative Spiralock self locking threaded fasteners. This re-engineered thread form adds a unique 30-degree wedge ramp at the root of the female thread which mates with standard 60-degree male thread fasteners.
The wedge ramp of the self-locking threaded fasteners allows the bolt to spin freely relative to female threads until tension is created in the male fastener. The crests of the standard male thread form are then drawn tightly against the wedge ramp, eliminating radial clearances and creating a continuous spiral line contact along the entire length of the thread engagement. This continuous line contact spreads the clamp force more evenly over all engaged threads, improving resistance to vibrational loosening, axial-torsional loading, joint fatigue, and temperature extremes.
The innovative threaded fasteners with a locking feature integrated into the thread form compensates for variations in manufacturing tolerances and processing. This locking feature enhances joint reliability, which can help reduce potential liability. By eliminating the need for secondary thread locking devices or procedures, it also simplifies assembly, maintenance, and inventory management.
When a design engineer began work on a rotating control device (RCD) prototype for a major oil services company, for instance, the decision was made to use the Spiralock thread form to help enhance its design reliability and production uptime.
During drilling, RCDs help meet rig health, safety, and environment challenges by keeping a pressure-tight barrier between personnel on the rig floor and rig drilling fluid and gas returns.
The previous generation of RCDs had used a lock wire with a special cross-drilled bolt to keep certain fastened joints from coming apart. But wiring the screw head on the RCD required added time, labor, cost, and component space for service maintenance.
Instead, the Spiralock self locking thread provided vibration and temperature resistance without the cost or complexity of a lock wire and special bolt. This also shrunk the fastener footprint so it could fit a little more compactly into confined spaces, easing serviceability and operation. After testing and development, the RCD was successfully deployed in the field, and has contributed to improved production uptime.
“Traditional fastening methods leave room for improvement,” says Jeff Jungmann, a Spiralock Engineering Manager. “For instance, locking wires require a special bolt and take time to wire together; chemical adhesive application can be inconsistent and don’t work well in high temperature; and deformed threads can gall during initial assembly or lose effectiveness in later disassembly and reassembly.”
While Spiralock tapped holes and locking fasteners are used in a range of oil industry equipment from drill collars, cutting tools, and high pressure valves to down hole tooling and even mining shakers and separators for oil sands operations, engineers often become aware of its use in mission critical applications in other industries. It has been used in extreme fastening applications with virtually no chance of recall: from the main engines of NASA’s Space Shuttle; to the Saturn Cassini orbiter and Titan Huygens probe ; to medical implants, artificial limbs, and heart pumps. Besides being used in high vibration, high temperature diesel engine applications, the Spiralock locking fastener has been validated in published test studies at leading institutions including MIT, the Goddard Space Flight Center, Lawrence Livermore National Laboratory, and British Aerospace.
“Spiralock tapped holes and locking fasteners perform well in a high shock, heat, and vibration environment, particularly in the hard-to-cut super alloys like Inconel, P550, and MP35N, which are increasingly needed in deeper, more demanding well bores,” says Jungmann. “Since the locking component comes from its internal thread form, there’s no need for chemical adhesives or secondary locking features. It works with standard bolts and screws, which simplifies application and maintenance.”
Production changeovers to the self locking fasteners are typically quick and seamless, often requiring just an exchange of traditional nuts, wire inserts or simply drilling out and re-tapping existing parts stock. For resistance to corrosive salt water environments stainless steel fasteners are available, as is specialty tooling for super alloy materials.
For detailed test data, including comparative graphic loading characteristics or photoelastic analysis/load vector comparison animation, visit Spiralock at www.spiralock.com; email slinfo@spiralock.com; call (800) 521-2688; fax (248) 543-1403; or write to Spiralock at 25235 Dequindre Rd, Madison Heights, MI 48071.
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