Page 329 - Trenchless Technology Piping Installation and Inspection

288 Cha pte r Se v e n

a prescribed period of time. The workable life of a heat activated
resin can be extended using ice or refrigeration to keep the resin tem-
perature at a reduced level.
UV light activated resins are designed to cure when a UV light
source is applied for a short period of time. The workable life of a UV
light activated resin is typically equal to the resin life after being man-
ufactured. If the wet-out tube remains isolated from UV light, then it
can remain stored for weeks and months.
Ambient cured resins are designed to cure in a fixed period of time
at a predetermined temperature after the resin and the catalysts are
mixed together. Typically, if the ambient temperature is higher than
the baseline temperature, the resin cure rate will be faster, conversely,
if the temperature is lower, then the resin cure rate will be slower.
The primary function of the fabric tube is to carry and support the
resins until it is installed and cured. This requires that the fabric tube
withstand installation stresses with a controlled amount of stretch, but
with enough flexibility to dimple at side connections and expand to fit
existing pipeline irregularities. The fabric tube material can be woven or
nonwoven with the most common material being a nonwoven, needled
felt. Impermeable plastic coatings are commonly used on the exterior
and/or interior of the fabric tube to protect the resin during installation.
The layers of the fabric tube can be seamless, as with some woven mate-
rial, or longitudinally joined with stitching or heat bonding.
In addition to the type of resin, the primary differences between
the various CIPP systems are in the composition and structure of
the tube, method of resin impregnation (by hand, by vacuum, or by
pressure), installation procedure, and curing process. Typical CIPP
design properties are shown in Table 7.6.

7.3.1 Tube Wet-Out
Wet-out is the process of introducing the catalyzed resin liquid into
the fabric tube. Wet-out of a tube liner can be accomplished several
ways. The traditional wet-out is termed vacuum impregnation. Other
systems that are equally as efficient are resin immersion and resin
bath wet-out.

ASTM Test Polyester Vinyl Ester Epoxy
Property Method (psi) (psi) (psi)
Tensile strength D638-08 2000–2500 2500–3500 3500–4000
Flexural strength D790-07 4000–5000 4000–5000 4000–5000
Flexural modulus D790-07 250,000– 250,000– 300,000–
500,000 350,000 400,000

TABLE 7.6 Typical CIPP Design Properties