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Western Dam Engineering <br /> Technical Note <br /> <br /> May 2016 <br /> <br />15 <br />do not begin to cure if properly protected from light. <br />Resins cured with UV light can also be used to avoid <br />the environmental impact of some thermoset resins. <br />UV cured resins do not contain styrene but they are <br />more expensive than styrene-based resins. Since UV <br />curing is not heat dependent it has less shrinkage than <br />hot water and steam cure. UV cured CIPP has less than <br />0.5% shrinkage and hot water and steam cured CIPP <br />can have up to 12% shrinkage. However, UV liners are <br />limited in thickness and diameter because the thicker <br />the liner and the farther its surface is from the light <br />source, the less intense, and less effective the light is <br />at curing the resin. Typical UV liners are limited to <br />about 0.5- to 0.6-inch thick and about 50 inches in <br />diameter. <br />Ambient <br />This method of curing is generally not recommended <br />because it takes longer for the resin to cure and the <br />temperature is not as easily controlled resulting in a <br />lower quality product. The CIPP can be cured at <br />ambient temperatures above 65 degrees Fahrenheit, <br />or at the temperature recommended by the resin <br />manufacturer. However, ground temperatures within <br />dams are typically below 60 degrees limiting the <br />effectiveness of this technique. <br />Termination and End Seals <br />After the curing process is complete, the ends of the <br />CIPP liner are trimmed flush with the ends of the <br />existing pipe, as needed, and any air vents or other <br />service connections are cut and smoothed and the <br />ends of the CIPP are treated. The ends of the CIPP can <br />be treated using mechanical seals, grinding the ends of <br />the CIPP smooth, or using epoxy. With smaller <br />diameter pipe, where access inside the pipeline is <br />limited, a robotic remote controlled device can be used <br />inside the pipeline to make the necessary cut outs. As <br />required by the contract or purchase agreement, <br />samples of the CIPP can be tested for flexural and <br />tensile strength and chemical resistance. <br />Thermosetting setting resin systems have different <br />shrinkage properties, both radially and longitudinally. <br />The design length of the as-shipped CIPP liner should <br />consider the potential for longitudinal shrinkage. <br /> <br />Table 2. Comparison of Curing Methods ADVANTAGES CONSIDERATIONS <br />Hot Water <br /> Historically proven method <br /> Ability to address sags/standing water <br /> One uniform temperature throughout pipe <br /> Accommodates long lengths/large diameters <br /> Consumption of Water to inflate/cure <br /> Height access for inversion towers <br /> Steep slope limit due to weight of water <br />Steam <br /> Less time to complete curing <br /> Higher degree of cure = higher properties <br /> Allows for steep slope installations <br /> Limited water supply and access required <br /> Safety considerations of steam use <br /> Length and thickness limitations <br /> Potential of coating to blister from heat <br />UV <br /> Glass fiber allows for reduced laminate thicknesses <br /> Accommodates both polyester and vinylester <br />resins <br /> Styrene barriers minimize environmental impact <br /> Shelf life up to six months; no refrigeration <br /> Ability to view liner before it is cured <br /> Ability to accommodate and control pipe seepage during <br />installation <br /> Size limitation of 6-48" <br /> Typically slightly higher cost compared to felt CIPP <br /> Minimal expansion capability for abnormal pipes <br />Ambient <br /> Minimal curing equipment <br /> Less expensive Requires ambient temperatures above 65oF, which is uncommon in dam outlet works pipes. <br /> Longer cure duration and limited temperature controls may lead to reduced quality <br />Adapted from inlinerTM technologies [6]