Fasteners and Sealing
Full contact along the entire engaged length of the thread reduces thread galling and enables fastener reusability up to 40 times or more, reducing the need for replacement parts. The locknuts are actually free spinning until they’re torqued down and locked in place, easing maintenance.
Ryan Bostick, STANLEY Engineered Fastening specialist.
cut super alloy materials, while enabling extensive reusability in the field. Traditional 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.
Easing reusability
Engineers, however, have successfully attacked these challenges while easing reusability, assembly, maintenance and inventory management with Spiralock self-locking threaded fasteners. The self-locking thread form is used in a range of oil and gas applications from MWD chassis, top drives, reamers, and set screws, to high pressure compressor valves, vertical and OHH pumps, and even mining shakers and separators for oil sands operations. This re-engineered thread form, offered by the Spiralock brand of STANLEY Engineered Fastening, 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. Whether as tapped holes or locknuts,
the innovative threaded fasteners with a locking feature integrated into the thread form enhance joint reliability and enable extensive reusability, while eliminating the need for secondary
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thread locking devices or procedures. “The thread form is not only self-
locking but also reusable without damaging the locknut or bolt,” says Ryan Bostick, a STANLEY Engineered Fastening, oil and gas technical sales specialist for the Spiralock brand. “Full contact along the entire engaged length of the thread reduces thread galling and enables fastener reusability up to 40 times or more, reducing the need for replacement parts. The locknuts are actually free spinning until they’re torqued down and locked in place, easing maintenance.” NASA tests, in fact, found the Spiralock-thread fasteners delivered 50 uses with no loss of clamp load. The thread form was used in the main engines of the Shuttle orbiter, with its tremendous launch vibration and repeat servicing requirement. When oil services company designed
MWD equipment, it sought to resolve the downhole issues of extreme shock, vibration, and temperature more effectively than using adhesives. MWD equipment, which measures properties such as pressure, temperature, and wellbore positioning in three dimensional space, is vital to enable extended-reach drilling (ERD), both offshore and onshore. If MWD equipment breaks in the wellbore due to loose screws, and the equipment must be brought to the surface from deep below ground or sea, it can cost more than $500,000 in lost production costs.
Vibration resistance
Instead of traditional adhesives, the tapped Spiralock self-locking thread provided vibration and temperature resistance without requiring adhesive application or clean up. Today, after testing and deployment,
the self-locking thread enables reuse on a variety of MWD chassis applications, including logging-while drilling (LWD) tools that measure ground formation variables such as porosity, resistivity, gamma ray, and sonic velocity; and photomultiplier tube (PMT) tools that measure refracted light from the soil to determine nearby resources such as oil, carbon, or water. l
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