Study of corrosion resistance of pump-compressor pipes made of ferrite-pearlite steel under the action of carbon dioxide mediums

To ensure required complex of steel strength properties, pipes heat treatment is widely used as a quenching for martensite followed by tempering. It is accepted, that metal microstructure formed at that, has a little effect on a steel corrosion resistance in carbon dioxide mediums. Studies were accomplished of steel microstructure effect of the carbon dioxide corrosion speed. In particular, a low-alloyed structural steel, used for production of oil field pipes was selected. As the object of the study, seamless pumpcompressor pipes (PCP), made of medium-carbon steels of several grades with chrome content about 1% (mass.), subjected to two methods of heat treatment: quenching with tempering or normalization with tempering. Corrosion resistance of the steels were accomplished under laboratory conditions of JSC “RusNITI” by application of autoclave facility imitating operation conditions parameters of a working medium at oil extraction. The speed of general metal corrosion was measured as samples mass loss during tests (from 360 to 70 hours) by gravimetric method. By the results of laboratory tests the steel 35ХГФА was recommended to the industrial production of PCP of K72 and N80 strength groups due to GOST 31446 with normalization and tempering. It was established that pipes of steel 35ХГФА with ferrite-pearlite microstructure have higher corrosion resistance in mineralized water mediums at carbon dioxide partial pressure up to 0.20 atm, comparing with regular pipes, manufactured with quenching and tempering. A complex of field tests of PCP was carried out, the pipes made of experimental steel 35ХГФА at an oil deposit. The result of operation of CPC of 88.9×6.45 mm made of steel 35ХГФА having K72 group of strength (after normalization with tempering) during 550 days under conditions of high-mineralized water phase at СО2 partial pressure up to 0.27 atm was found positive. After an intermediate inspection (550 days) the column of PCP was assembled and is in operation at present, the current running time exceeding 1000 days. Based on the results of the complex comparative tests carried out in the corrosion laboratory and under field oil extraction conditions it was established that usage of experimental steel 35ХГФА containing 1% of Cr, after application of normalization technology with tempering resulted in increasing of operating reliability of CPC.