Page 487 - Trenchless Technology Piping Installation and Inspection

Glossary of Terms 437

Viscosity: That property of a fluid which determines the amount of its
resistance to a shearing stress.
Voids: (1) Holes on the outside of the pipe in the surrounding soil or
material. (2) A term generally applied to paints to describe holidays,
holes, and skips in the film. Also used to describe shrinkage in castings or
welds.
Walkover system: See locator.

Washover pipe: In horizontal directional drilling, sometimes (for drilling
in rock) a rotating drill pipe of larger diameter than the pilot drill pipe is
used and placed around it with its leading edge less far advanced. Its
purpose is to provide stiffness to the drilling pipe to maintain steering
control over long bores, to reduce friction between the drill string and the
soil and to facilitate mud circulation.
Water jetting: (1) Method for the internal cleansing of pipelines using
high-pressure water jets. (2) An obsolete and unauthorized method for
cutting earth with water jetting.

Water table: (1) The depth of the ground water. (2) The upper limit of the
portion of ground wholly saturated with water.
Weatherability: The properties of a plastic material that allows it to
withstand natural weathering; hot and cold temperatures, wind, rain,
and ultraviolet rays.
Wetout: The process of injecting resin into, and distributing it throughout,
a hose or tube, which will then be installed into the pipeline and cured in
place.
Winch: Mechanical device used to pull the CCTV cameras or cleaning
tools through a pipe.