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Figure 1: Comparison Of Lining Thickness Of Two Lining Systems water. The steel pipe was free of corrosion due to passivation of the steel surface provided by the mortar lining. This line was in service for almost 70 years before the first mortar lining standard for cast- iron pipe (AWWA C104) was developed in 1922. Cement mortar-lined steel pipe was first used in the United States in the late 1800s, and mortar linings continue to be the predominant means to protect the interior of buried large-diame- ter steel water pipelines from corrosion. Besides being used on steel pipes, the need for a better lining to combat tuberculation at pinholes of hot-dip bituminous-lined cast-iron pipe led to the first use of portland cement mortar linings in cast-iron pipe in 1922 (AWWA C104). Use of mortar lining in water transmission steel pipelines for at least the past 50 years is estimated at greater than 95%. The remaining small percentage of steel water pipelines that do not use portland cement lining systems are typically penstocks and above-ground pipelines. Portland cement mortar is also the predominant lining system for cast- and ductile-iron water pipelines. Portland cement mortar or portland cement concrete is always used as the lining system in concrete pressure pipe. Mortar lining application requires minimal, if any, surface preparation of the steel. Abrasive blast and a surface profile are not necessary, and minor corrosion and mill scale on the steel surface do not affect the corrosion-inhibiting (passivation) properties of the mortar lining. It can be applied at temperatures from 40°F to 95°F (4°C to 35°C) with no concern for dew point requirements and under all humidity conditions. The passivating property of portland cement mortar is due to calcium oxide and small quantities of potassium and sodium ions BELOW This is an example of the application of mortar lining to the interior of steel water pipe by centrifugal spinning. in portland cement that convert to calcium, potassium, and sodium hydroxides when water is added to the cement and sand mixture immediately prior to application of the lining to the interior of the steel pipe. This hydration process produces a high pH environ- ment — greater than 12.5. At this pH, steel passivates and does not corrode, provided a combination of substantial chloride ions and oxygen is prevented from reaching the steel surface. Diffusion of water and oxygen, with the amount of chloride ions found in potable water, through the mortar lining does not reduce passivation. Mortar linings are very durable with an estimated material and application cost of $0.50 to $0.75 per square foot of steel surface area. This cost is the least expensive of the various lining systems used on steel pipe and is due to the lower material cost of sand and cement, the negligible steel surface preparation required, and the ability to line in any humidity condition and under a wider range of temperatures than typical dielectric materials. In addition to corrosion protection, mortar linings also contribute substantially to pipe stiffness, which the other lining systems do not. COAL TAR ENAMEL Coal tar enamel (CTE) linings have been used on water pipelines since the mid-1930s (AWWA C203). The primary reason for its excel- lent performance is due to the 3/32" (2.4 mm) thickness of the lining that had been typically applied when compared to the much thinner linings used in the other dielectric lining systems. The use of CTE has decreased substantially during the past two decades due to its suspected carcinogenic nature, its volatile organic compound (VOC) content, and the odor emitted during application, which caused strin- gent permitting requirements for its use in populated areas. These issues have forced some water agencies to curtail specifying CTE and some pipe manufacturers from applying CTE to pipe. It is estimated that less than 1% of steel pipelines in service are lined with CTE. The application of CTE requires a minimum commercial blast (NACE No. 3/SSPC-SP6) with a surface profile of 1.5 mils to 3.5 mils (38 to 89 microns) and a metal temperature greater than 5°F (2.7°C) above the dew point. Due to the lack of use of CTE linings, no current cost data is available. LIQUID AND FUSION-BONDED EPOXIES From 1941 until 1978, portland cement mortar and coal tar enamel were the only two lining materials listed in AWWA standards. In the 1950s, liquid epoxies began to be used on oil and gas pipelines, and the first AWWA standard for liquid epoxy systems (C210) was approved in 1978. In the 1960s, fusion-bonded epoxy (FBE) systems began to be used on gas pipelines, and the first AWWA standard for FBE systems (C213) was approved in 1979. Liquid epoxies and FBE make up less than 3% and 1% of the linings on large-diameter steel water pipe, respectively. Liquid epoxies can be applied by brush, roller, or spray, and this flexibil- ity in application methods eases their use in fittings and special sections of pipe. The inherent characterist ics of epoxies make them relatively rigid as they age, and the required thickness of July 2012 J www.coatingspromag.com 51