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Initially, a steel cylinder is fabricated to
serve as a water-tight membrane and to provide axial and beam strength
to the pipe. Precisely sized steel joint rings are attached and
welded to each steel cylinder. The fabricated cylinder is hydrostatically
tested to an internal unit stress of at least 137.9 MPa (20,000psi)
in the cylinder wall.
The tested cylinder is then lined with a centrifugally
cast concrete to constitute the core. The nominal thickness of the
concrete and steel core is 1/16th of the inside diameter of the
pipe. The core is then cured to assure its high strength.
Next, the core is wrapped with an evenly spaced
helix of high tensile strength prestressing wire. The prestressing
wire is wrapped directly on the steel cylinder under a constant
tension of 75% of its minimum ultimate strength. For a selected
wire size, the tension and spacing of the wire are controlled to
induce a predetermined compression in the concrete. The compression
induced in the core is such that, at the highest working pressure,
considerable reserve core compression remains. Due to predictable
stress losses which occur after the pipe is prestressed, the tension
in the wire at the time of wrapping is greater than at any time
during the service life of the pipe.
As the process continues, a dense cement-rich
mortar coating is placed by high velocity impaction over the prestressed
core, then cured. The mortar coating has a minimum thickness of
19mm (3/4in.) over the wire. It provides additional structural strength
as well as positive protection for the steel wire and cylinder.
The advent of high strength prestressing wire
brought about the development of this product which utilizes the
best characteristics of concrete and steel. The compression in the
concrete and the tension in the steel work in unison to provide
a rugged, high strength (rigid) pipe with minimal weight. This pipe
has been designed for operating pressures greater than 2.758KPa
(400psi) and earth covers in excess of 30m (100ft).
Hyprescon manufactures LCP from 400mm (16in.)
to 1500mm (60in.) diameters at the Stouffville, Ontario facility
and the St. Eustache, Quebec facility.
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