Causes and Prevention of Failures in Cement Pipe Linings

Abstract

Because durable pozzolan-cement linings could not be produced by simple, economical methods, efforts were redirected toward sand-cement linings. The results are better linings that have strength, uniformity, and inertness, and that are expected to be long-lived enough to be economical. Introduction "Cement-lined" is the term commonly used and recognized in describing pipe with a lining in which portland cement is the binder for sand or pozzolan. Cost portland cement is the binder for sand or pozzolan. Cost and technical considerations discourage the use of linings made of pure cement. Partial replacement by sand or pozzolan is said to benefit cement and is known to reduce its cost. During the past several years, applicators have cement-lined many miles of steel pipe to carry corrosive water. Oil producers in the Southwest have installed this pipe in distribution systems between water supply wells and waterflood injection wells. The investment in these installations is several millions of dollars. The floods consume large volumes of water from systems that require pipe as large as 24 in. in diameter to supply demands. In and country, there are priorities on potable water, so water for flooding must be obtained from brackish sources. One important source, the Capitan Reef - known locally as the Hendricks Reef - is a prolific aquifer in West Texas, but, as the following analysis indicates, it yields flood water corrosive to steel. pH 6.9 pH 6.9 sodium 3,014 ppm calcium 900 ppm magnesium 292 ppm bicarbonate 400 ppm chloride 4,964 ppm sulfate 2,594 ppm hydrogen sulfide 102 ppm Portland cement combined with sand or pozzolan is a relatively inexpensive lining material and is less affected by this water than is steel. Applicators and users have learned that a particular cement, ASTM Type III containing no tricalcium aluminate, has special resistance to sulfate and other corrosives in this or similar water. The economics of lining pipe requires a rapid means of applying a uniform internal layer of cementitious solids. At present, centrifugal casting is the only feasible method of doing this. In this process a joint of pipe, usually 40 ft long, is mounted in powered rollers. A water slurry with enough solids to form powered rollers. A water slurry with enough solids to form a lining is added, and the pipe is rotated at peripheral speeds of approximately 1,000 linear feet per minute. A minute or two is sufficient spinning time to deposit the solids, compact the layer, and separate excess water. The pipe is then taken to a shed into which steam is injected, and the pipe stays in a moist atmosphere of 120 degrees to 150 degrees F for about 18 hours. Next, the lined joints are flooded with water, capped, and placed in storage where they remain a month or two before going into service. Seventy percent of Type III cement used in linings is tricalcium silicate (C3S, an abbreviation, not a chemical formula). The events of C3S hydration dominate lining technology. As each C3S unit combines with water, it releases two units of lime, Ca(OH)2. JPT P. 51