Effect of Supercritical Carbon Dioxide (CO2) on Construction Materials
Authors: Schremp F.W. , Roberson G.R. 
Published: December 2007

Abstract
Laboratory tests showed that properly welded X-60 pipeline steel was not susceptible to environmental failure in supercritical carbon dioxide (CO2); and corrosion rates were less than 0.02 mils penetration per year (MPY). Other tests showed penetration per year (MPY). Other tests showed nonmetallic seals to be susceptible to damage. Seals constructed from Teflon, nylon, semi-rigid polyurethanes and ethylene-propylene rubber were polyurethanes and ethylene-propylene rubber were acceptable. Thin-film coatings and centrifugally cast cement also were acceptable pipe linings.

Introduction
Operation of the SACROC carbon dioxide-miscible secondary recovery project involves gathering, pipelining, and injecting more than 200,000,000 pipelining, and injecting more than 200,000,000 scf/D of carbon dioxide (CO2) into selected wells at a pressure of 2,400 psia. Waste CO2 is collected at approximately ambient conditions from four natural gas stripping stations. Thirteen compressors, totaling nearly 75,000 hp, are used to compress the gas to 2,000 to 2,400 psia. The gas is transported 232 miles in a 16- and 12-in. diameter pipeline to the Kelly-Snyder field, Scurry County, pipeline to the Kelly-Snyder field, Scurry County, Tex., where an additional 6,500 hp is used further to compress and to inject the gas at 2400 psia. Composition of the waste CO2 varies at each of the four stripping stations. The gas may contain 3 to 15 percent light hydrocarbons (chiefly methane), with up to 300 ppm hydrogen sulfide and a water content up to saturation. According to pipeline specifications, the mixed high-pressure gas contains at least 90 mol percent CO2 with the balance consisting of C1-C6 hydrocarbons. The mixed gas also contains less than 50 ppm water vapor and less dean 300 ppm hydrogen sulfide. In service, the line temperature varies from 45 to 120 degrees F. Before construction, it was necessary to know how supercritical CO2 would affect welded X-60 pipeline steel and other materials that might be used pipeline steel and other materials that might be used in the system. Laboratory tests were made after a literature search failed to produce the needed information.

APPARATUS
The apparatus used to simulate SACROC CO2 pipeline conditions is shown in Fig. 1, which shows pipeline conditions is shown in Fig. 1, which shows that the CO2 charging system consists of a source of CO2, a molecular sieve desiccator, a Sprague compressor unit, and an accumulator. Compressed CO2 is stored in the accumulator at 3,500 psig and nitrogen is used to maintain the pressure. When needed, hydrocarbon gas also can be supplied separately to the accumulator. Compressed CO2 at 2,000 psig is supplied from the accumulator to each of the three test cells via a regulator and check valves, V-37 and V-38. Test Cell 1 has a separate pump to circulate the CO2. Test Cells 2 and 3 are connected in series with a second circulating pump. Pump velocities can be varied but usually are set to develop a lineal flow rate of 30 to 40 in./min in the test cells. Test Cells 1 and 2 are equipped with Panametrics hygrometer probes to monitor the water content. probes to monitor the water content. The test cells also have connections to inject H2S and water and to sample the gas composition. Hydrogen sulfide content is monitored with Kitagawa detector tubes (0.01 to 0.17 volume percent). Test temperature is maintained at 72 2 degrees F. Heating mantles (not shown) can be attached to the cells to maintain a temperature of 130 degrees 2 degrees F when needed.

WELDED X-60 PIPELINE STEEL TESTS
The purpose of these tests was to determine the effect of simulated SACROC CO2 pipeline conditions on field-welded X-60 steel. Six manufacturers were contacted and from each were obtained samples of pipe that were at least 12 in. in diameter and with pipe that were at least 12 in. in diameter and with a minimum wall thickness of 0.344 in. Compositions of the pipe samples appear in Table 1.
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