Abstract
C110 oil well casing tubes should have high strength and corrosion resistance which is commonly used for deep wells operation containing corrosive media. In this paper, the microstructure evolution of a kind of semi-macro segregation originated banded structure in casing tubes is studied under different heat treatments. It is shown that the characteristics of the banded structure will change significantly in subsequent hot working and heat treatment processes. For the hot-rolled ones, the banded structure is composed of pearlite plus bainite. After quenching, it evolves into martensite band with high concentration solute elements. Finally, the banded structure will change into a carbide banding under the following tempering process. The temperature and cooling rate of the tempering practice show an obvious effect on the final band structure. To improve anti-SSC (sulfide stress corrosion cracking) performance, the favorable QT (quenching and tempering) practice for C110 steel should be a higher tempering temperature and a quicker cooling rate, from which the banded structure defects can be decreased together with an obvious improvement of the tube wall hardness uniformity.
Highlights
Casing and tube steels that are used in oil and gas fields with high pressure and aggressive corrosion environment require both high strength and high corrosion and hydrogen embrittlement (HE) resistance [1,2,3]
Any significant as-cast defects such as macro or semi-macro segregations will lead to a non-uniform microstructure in the final products which is detrimental to its hydrogen SSC resistance [8,9]
Some of the as-quenched samples were tempered at 705 ◦ C for 2 h followed by air cooling or water quenching, marked as QT1, QT2, respectively, while the other as-quenched samples were tempered at 505 ◦ C for 2 h followed by air cooling or water quenching, which were labeled as QT3 and QT4 respectively
Summary
Casing and tube steels that are used in oil and gas fields with high pressure and aggressive corrosion environment require both high strength and high corrosion and hydrogen embrittlement (HE) resistance [1,2,3]. C110 grade oil casing steel is one of highest grade corrosion resistant products with a minimum yield strength requirement of 758 Mpa. During service, there is usually a popular HE failure of the steel for deep oil and gas wells operation containing wet hydrogen sulfide (H2 S), which is known as SSC [4]. For the quality production of C110 casing tubes, the chemical composition and thermomechanical treatment processing are the main factors that can be optimized to obtain the most suitable microstructure to achieve high strength with superior SSC resistance. Any significant as-cast defects such as macro or semi-macro segregations will lead to a non-uniform microstructure in the final products which is detrimental to its hydrogen SSC resistance [8,9]
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