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