A gap sub assembly and methods for using the gap sub provide an electrical isolating joint that is mechanically strong enough to withstand the rigors of drilling environments, resistant to environmental effects (heat, corrosive liquids and gases, and high pressures), and maintainable. The gap sub assembly provides a male member and a female member that may be connected together, wherein a non-conductive material is applied between the two at the attachment points. A locking ring or collar affixes to both male and female members to prevent back off while drilling and preserving the electrical isolation of the gap joint. Non-conductive material may be injected between the locking ring and one or more of the male or female members.

An insulating collar for a gap sub assembly for electromagnetic (EM) telemetry used in downhole drilling is disclosed. The gap sub assembly comprises a female member comprising a female mating section and a male member comprising a male mating section and a gap section. The male mating section is matingly received within the female mating section and electrically isolated therefrom. The insulating collar is positioned on the gap section. The collar is made up of a framework with a plurality of discrete bodies spaced about the framework and a portion of each of the discrete bodies protrudes above the framework. Either the framework or the discrete bodies are made of an electrical insulator material to electrically isolate one end of the collar from the other end of the collar. The collar therefore electrically isolates the male member from the female member and the male member, female member and insulating collar function as the gap sub for EM telemetry.

The invention comprises dielectric isolators for use in aircraft fuel systems to control lightning induced current and allow dissipation of electrostatic charge. The dielectric isolators are configured to have a high enough impedance to limit lightning currents to low levels, but low enough impedance to allow electrostatic charge to dissipate without allowing buildup. Although the dielectric isolators may develop a potential difference across the dielectric length due to the effects of lightning currents and its inherent impedance, they are configured to withstand these induced voltages without dielectric breakdown or performance degradation. In one embodiment, the dielectric isolator includes a tube constructed of a composition including a thermoplastic organic polymer (e.g., PEEK) and carbon nanotubes, and a pair of fittings attached to opposing ends of the tube. In another embodiment, the dielectric isolator includes a tube, an outer annular portion, and an interconnecting web, each constructed from the composition including a thermoplastic organic polymer (e.g., PEEK) and carbon nanotubes. This later embodiment is an integrally formed one-piece structure. The dielectric isolator is capable of exhibiting an electrical resistance from about 10.sup.5 to 10.sup.8 at an applied potential of greater than 500 volts DC when measured from one fitting to the other fitting.

A method and apparatus for joining first and second bodies coaxially together to resist relative axial and rotational movement between the bodies. A male portion of the first body is received in a complementary female portion of the second body, and the male and female portions are aligned axially on a common axis such that respective cooperating grooves in opposing cylindrical or tapered complementary surfaces of the male and female portions are aligned to form a plurality of passageways or a passageway having a plurality of passageway portions, between the opposing cylindrical or tapered complementary surfaces. At least two of the passageways or at least two of the passageway portions are disposed at different angles to the common axis. Solid mechanical coupling elements are loaded into each passageway or into the passageway having the plurality of passageway portions, such that each passageway or the passageway having the plurality of passageway portions is substantially full of the solid mechanical coupling elements.