State of Technology Report for Force Main Rehabilitation, Final ...

The above equations have been primarily developed for use with CIPP products, while the
deformed/reformed thermoplastic products have also adopted them. As there are few if any design
guidelines for spray-on coatings, the TTC has been carrying out some tests on spray coatings for the
rehabilitation of pressurized pipelines. The main purpose of the testing is to generate an empirical design
equation to determine the needed thickness of a polyurethane lining given an internal operating pressure
and size of damage zone. To do this, an experimental program has been conducted that consists of testing
panels of a spray-on polyurethane coating, which are clamped into a test frame and subjected to uniform
pressure on one side of the frame with the other side open to atmosphere. The openings in the test frame
have been 3 and 4.5 inches (75 and 113 mm) in diameter. In addition to monitoring the pressure at which
the test panels fail, the amount of deformation or bulge of the test panel was also measured and compared
to analytical and finite element analysis model predictions. At the time of writing this report, the TTC is
in the process of expanding the testing to other spray-on coatings (polyurea) with the intention to develop
a generalized equation that incorporates key mechanical properties of the coating materials. With new
structural spray-on lining systems entering the US market, this work will be very welcomed.
5.4.1.2 Fully Deteriorated Case. In the fully deteriorated case, the liner is designed to resist without
buckling all of the external loads, including groundwater, soil, negative internal pressure (vacuum), and
live loads. The equation offered in ASTM F1216 has been borrowed from the AWWA design manual for
Fiberglass Pressure Pipe, M45. The equation takes into consideration the soil support offered to the
original host pipe and the liner:
where:
qt = total external pressure on pipe (including negative internal pressure), psi
Rw = water buoyancy factor (0.67 min. – see F1216 for equation)
B’ = coefficient of elastic support (see F1216 for equation)
I = moment of inertia = t 3 /12, in 4 /in
D = mean inside diameter of the original pipe, inches
C = ovality reduction factor
N = factor of safety
E’s = modulus of soil reaction, psi
El = long-term modulus of elasticity, psi
Values for the modulus of soil reaction may be found in ASTM D3839.
As the liner pipe must be capable of supporting the full internal pressure without support from the original
pipe, the required design thickness may be calculated from the following formula which relates the hoop
tensile stress in a thin ring to the internal pressure:
where:
P = internal pressure, psi
σTL = long-term (time corrected) tensile strength, psi
DR = dimension ratio (diameter/thickness) (D/t)
N = factor of safety
The note to this equation advises the user to choose a value for σTL from the manufacturer’s literature,
which is consistent with the estimated duration of the load. As was the case for the long-term flexural
modulus, EL, no specified test method is offered for determining the long-term tensile strength so it is left
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