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When specifying linings for—or applying them to— large-diameter steel water pipelines, there are some helpful facts to remember: t Portland cement mortar linings have been used on large diameter steel water pipelines for more than 175 years. t Service histories of dielectric linings vary widely. t Coal tar enamel (CTE) linings have been used on steel water pipelines since the mid-1930s. In the past several decades, usage has substantially declined due to its suspected carci- nogenic nature, odor, and VOC content. t Portland cement mortar is the predominant lining system for steel, cast-iron, and ductile-iron water pipelines. Portland cement mortar or concrete is always used as the lining system in concrete pressure pipelines. t Dielectric linings have limited performance histories. Any such application should anticipate regular inspection and maintenance. t Portland cement mortar linings are thick, durable, easily repaired, require essentially no steel surface preparation, can be applied in almost all weather conditions, passiv- ate steel, and retard oxygen diffusion to protect steel from corrosion. They contribute greatly to pipe stiffness in contrast to dielectric linings. t Portland cement mortar linings benefit from exposure to and penetration of water from the transported water while dielectric linings must be formulated to be impermeable to liquid water and water vapor. t Dielectric linings and portland cement mortar linings are smooth, resulting in similar Hazen-Williams flow coeffi- cients (C-factor) ranging from 140 to 155. t Portland cement mortar linings are considerably less expensive than dielectric linings, require less maintenance, and are easier to repair. t In seismically active areas, dielectric linings are expected to perform well. Portland cement linings have proven to have excellent performance in severe earthquakes conditions. 0.012" to 0.015" (0.30 to 0.38 mm) for FBE and the minimum thickness of 0.016" (0.41 mm) of the liquid epoxies make these linings susceptible to cracking due to the flexible nature of large-diameter steel pipes. As such, the epoxies specif ied need to be reviewed carefully to determine if they are appro- priate for project requirements and specified appropriately to reduce damage during shipping, installation, and backfilling. In addition, the typical service life of epoxies with periodic maintenance is up to 20 years and not the minimum 50-year life typically required for buried water pipelines. The application of the liquid epoxies requires a minimum near-white blast (NACE No. 2/SSPC-SP10) with a surface profile of 2.0 mils to 4.0 mils (50 to 100 microns) and a metal tempera- ture greater than 5°F (2.7°C) above the dew point. The application of FBE requires a minimum near-white metal blast (NACE No. 2/ SSPC-SP10) with no rust bloom and a surface profile of 1.5 mils to 4.0 mils (38 to 100 microns). 52 CoatingsPro J July 2012 ABOVE This photo shows the application of liquid epoxy lining to the interior of a rotating steel water pipe. A similar process is used for polyurethane linings. The estimated material and application costs of liquid epoxies range from $2.00 to $3.00 per square foot of steel surface area. In addition, the use of liquid epoxies, like all painted linings that depend on a substantial bond to the substrate, raises concerns regarding the ability to handle internal stresses in the film. These stresses are caused by the movement of the steel substrate due to pipe deflection and pressurization. Some formulations are better suited to handle these long-term stresses. Material and application costs of FBE are dependent on the throughput of the lining application process. The steel pipe needs to be pre-heated, and FBE requires large expenditures of energy to heat the steel pipe to 400°F to 500°F (200°C to 277°C). POLYURETHANES In 1999, a lining standard for polyurethanes (C222) for large- diameter steel water pipe was developed by AWWA. The inherent characteristics of polyurethanes tend to make them more flexi- ble and abrasion-resistant than epoxies and less prone to impact damage, but polyurethanes typically have a substantially greater water vapor transmission rate. Modifying the polyurethane formu- lation to tighten the molecular structure and reduce water vapor transmission also makes the resulting polyurethane less flexible. Polyurethanes can be formulated to harden in seconds, providing for easy handling of pipe shortly after lining. The liquid water and water vapor transmission of polyurethanes makes them relatively susceptible to disbondment due to corrosion under the lining. This under-film corrosion can be difficult to detect. Since many polyure- thanes have a liquid surface tension that prevents easy wetting-out of the steel surface, adhesion to the steel is more highly dependent on surface preparation and application techniques. Recent testing of polyurethanes after water exposure has revealed issues with loss of adhesion over time. This type of testing and physical property specification requirement requires further research. The application of polyurethanes requires a minimum near- white blast (NACE No. 2/SSPC-SP10) with a surface profile of 2 mils to 4 mils (50 to 100 microns) and a metal temperature greater