pipe ovality: better ovality for lower costs
Pick a number from 1 to 10. What are the
chances you would be able to choose the
correct number? Only 10%, right? What if an
inaccurate answer
might cost you thousands if not
hundreds of thousands dollars?
Chances are you would want to
enhance your odds from a 10% guess to a 99%
certainty for the correct number. This is
the value-added component that measurable
information in pipeline condition assessment
can provide. It takes the guesswork out of
the bid work. Providing critical pipe ovality
dimensions translates into right-sized
trenchless rehabilitation technologies.
Translation: you save money.
Most municipalities waste a great deal of
money when they rehabilitate pipes. They
typically use a conservative guess when
designing the lining for an existing
sewer using a cured-in-place thermosetting
liner. The majority of cities use the ASTM
F1216 Standard to calculate pipe ovality:
Ovality = (Maximum diameter- Mean
diameter)x100%
... all of which is divided by the Mean diameter
However, typically they have to make a best
guess at some of the variables in the design
equation. The final designed liner thickness
can vary, and the increase of liner thickness
by mm's or inches more than required can
result in hundreds of thousands of dollars of
unnecessary cost. Just how much excess cost,
of course, depends on the diameter of the
pipe, the linear feet, and the liner thickness.
Today's newer trenchless rehabilitation
technologies have allowed authorities and
engineers to approach underground
construction projects from a different angle.
Laser and SONAR cross sections obtained from
precision scans provide accurate,
quantitative information on pipe ID,
including ovality and eccentricity. Ovality
and eccentricity are measured from the
horizontal and vertical pipe diameters. While
new construction verification is typically
straightforward, obtaining vertical diameter
in a partially charged pipe is more
difficult. With laser technology, you can
disaggregate the vertical diameter into two
radial segments. The first vertical radial
segment is called the crown radius -- it can
be obtained directly from the 3D Spinning
Laser data. The second vertical segment is
called the invert radius. The invert radius
is currently taken from the sonar data or
derived from as-built data. With the crown
and invert radius known, precise numbers for the
ovality calculation is now possible. Precise
dimensions and numbers translate into liners
that are designed as thick as they need be,
but not overly thick and needlessly expensive.
A more accurate value for sewer pipe's
ovality, obtained by means of laser
technology throughout the sewer pipe length,
will give a more accurate computation of the
liner's wall thickness. A more accurate
liner wall thickness correlates into a safer
and more cost effective trenchless technology
rehabilitation project.
