Angular Deflection

Published: | Updated: August 31, 2020;

Definition - What does Angular Deflection mean?

Angular deflection is the amount of deviation from a straight line that results when a pipe coupling is displaced under a load. Deviation due to deflection can occur because of problems with the drill, operator error, or due to unforeseen subsurface conditions.

Unchecked deviation from planned bore path can have serious consequences, especially in places where several underground utilities like gas pipelines, electric and cable connections, and sewer pipes, crisscross in and around the planned path.

Trenchlesspedia explains Angular Deflection

Angular deflection is a factor in the design and inspection of underground pipes and is an important factor in trenchless construction projects. Boreholes are designed after a thorough geotechnical investigation to prevent problems like sinkholes and cross boring through existing pipelines. Technically, borehole deviation defines the geometric difference between planned and actual bore paths. Based on the nearest point on the planned path, there are two types of deviations - linear and angular.

Factors That Affect Deviation While Drilling

Deviations that take place in the horizontal and vertical direction are called lineal deviations, while angular differences are azimuth and inclination deviations. It can be affected by factors such as soil stratification and drilling characteristics. Some factors that influence deviation are:

  • Rocks encountered during drilling.

  • Loose and old drill rods.

  • Loose-fitting core barrels.

  • Applied weight-on-bit (WOB).

  • Improperly placed stabilizers.

  • Improper drilling force.

  • Wrong bit design.

  • Buckled drill rods due to excess force while drilling.

  • Drilling too fast or too slow.

Setup process error at the beginning of a project can also cause deviation. To keep the bore path in the planned route and control deviation, a tool called measurement while drilling (MWD) is installed in the drill head. It uses a gyroscope, magnetometer, and accelerometer which are installed in the drill head and transmits real-time drilling parameters to the operator.

Deviation in Installed Pipes

When a pipe joint is under load, it may bend. The value of that bending is called angular deflection. The bending usually takes place at the centerline of the pipe coupling. Weak pipe joints can eventually result in leaks or other problems in underground systems.

Such vulnerabilities may be detected through routine remote or manual inspection of pipes. The investigation can be carried out remotely using closed-circuit-television (CCTV). With advanced technology in the robotic inspection of pipelines, it is also possible to navigate around bends and inspect hard to reach areas.

The values gathered during an investigation may be collected for later reporting or assessment purposes. The testing of pipes may reveal the need for trenchless rehabilitation or replacement of pipes.

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