CIPP Best Practices

By By NASSCO member Ed Kampbell, PE, Jason Consultants | October 2011, Vol. 66 No. 10

When the nose sees less than the minimum head longitudinal finning in the bottom half of the CIPP is almost a sure thing. Raising the head after inversion can only stretch the portion of the tube’s circumference that is not already in contact with the host pipe, creating a thin area in the crown of the CIPP. Also, if there is active infiltration observed in the host pipe an additional head equal to the level of the groundwater above the flowline of the host pipe must be added to the minimum inversion head.

Curing of the resin system
Resins used in CIPP are either heat cured or UVlight cured. With heat curing methods the water or the air is heated to a level that ramps up the speed of the polymerization process to effect hardening of the resin system. Minimum temperatures that must be seen at the interface of the CIPP with the host pipe established by the resin system manufacturer must be measured at as many points as are practical to insure that sufficient heat is being transferred throughout the liner’s wall section.

For hot water curing it is important to recognize that “heat rises”; for pipes larger than 18-inches in diameter, the water discharge tubing must be weighted to adequately heat the bottom of the CIPP. For CIPP cured by hot air (air with steam), condensate removal is imperative to avoid isolating the bottom of the CIPP from proper heating. Initial (or visual) hardening indicates that the curing has reached only the 80% cured level and complete curing requires the heating process be continued for the resin manufacturer’s minimum amount of time beyond the initial curing to insure complete curing.

As with heat curing, UV-light initiated resin systems must be exposed to the lighting for the minimum time required to fully cure; short changing the exposure time will result in an under-cured CIPP. Given the thinner cross-sections and the dependence on bringing the glass fibers into play makes obtaining a complete cure a top priority. Complete curing, whether by heat or UV-light, gives the CIPP its chemical resistance and structural properties.

Once curing is completed, the hardened CIPP must be brought down to a temperature where it is dimensionally stable. If the internal pressure is taken away before the CIPP has cooled down, the uncontrolled cool down can lead to an excessive gap between the CIPP and the host pipe. This shrinkage occurs with all the resin systems currently used for CIPP; polyester, vinyl ester, and epoxy.

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