Page 147 - Trenchless Technology Piping Installation and Inspection

Coatings and Linings for Potable W ater Pipe Distributions 113

Polyurethane linings are based on the exothermic reaction
between di- or poly-isocyanates and compounds with hydroxyl
end-groups such as polyols. It is the exothermic nature of this reac-
tion that provides fast-setting, cold-temperature curing ability, and
unlimited film build-up of polyurethane linings. Polyurethane
linings consist of sprayable and castable versions. The sprayable
version involves lining in various formulations having a mix ratio
of 1:1 with balanced viscosity between base and hardener. The cast-
able version is basically a mix, pour, and cast method of application.
Figure 3.11 shows a typical sprayer used for polyurethane applica-
tion. Table 3.8 represents advantages and limitations for poly-
urethane linings.

FIGURE 3.11 Polyurethane lining spray head. (Source: 3M Water Infrastructure.)

Advantages Limitations
1. Exhibits good chemical and impact 1. Poor adhesion with the
resistance. existing pipe.
2. Inner chemical structure with much less 2. Polyurethane is moisture
cross-linking that allows for the lining’s sensitive.
elastic nature. 3. Polyurethane has higher
3. Cures in minutes to an hour. permeability rating than
4. Offers the added benefit of better safety polyurea.
and environmental parameters when 4. May be more expensive
compared to the solvent-based materials. compared to other linings.
5. Good abrasion resistance.
6. Very flexible and can withstand large
movements and bends before displaying
cracking or disbondment.

TABLE 3.8 Advantages and Limitations for Polyurethane Linings