Ultra-fine grained steels having corrosion-fatigue resistance

Abstract

Embodiments of an ultra-fine-grained, medium carbon steel are disclosed herein. In some embodiments, the ultra-fine grained steel can have high corrosion fatigue resistance, as well as high toughness and yield strength. The ultra-fine grained steels can be advantageous for use as sucker rods in oil wells having corrosive environments.

Description

BACKGROUND[0001]1. Field[0002]Embodiments of the present disclosure relate to ultra-fine grained steels which can have excellent toughness and high fatigue resistance in corrosive environments.[0003]2. Description of the Related Art[0004]A sucker rod is a steel solid bar, typically between 25 and 30 feet in length, upset and threaded at both ends, used in the oil and gas industry to connect components at the surface and the bottom of a well. Sucker rods can be used in, for example, reciprocating rod lifts and progressive cavity pumping systems. Due to the alternating movement of the system, fatigue is a common failure mechanism of sucker rods in service.[0005]Typically, there can be a strong correlation between fatigue strength and tensile strength for steels up to about 170 ksi. However, under the effect of a harsh environment, which very frequently occurs in oil wells, the correlation may no longer be valid because the presence of hydrogen sulfide (H2S), carbon dioxide (CO2), chlo...

AI Technical Summary

Benefits of technology

The patent describes a new steel sucker rod that has better fatigue resistance and corrosion resistance compared to conventional sucker rods. The steel composition includes specific amounts of carbon, manganese, chromium, silicon, niobium, titanium, boron, and aluminum. The final microstructure of the steel is tempered martensite, with an average grain size between 2 and 5 micrometers. The steel can also have additional elements such as vanadium, nickel, and phosphorus. The method of manufacturing the steel sucker rod involves hot rolling, austenitizing, quenching, and tempering the steel composition to form tempered martensite. The technical effects of the new steel sucker rod include improved fatigue resistance and corrosion resistance, as well as better mechanical properties and resistance to damage from corrosion fatigue under CO2 or H2S environments.

Problems solved by technology

Due to the alternating movement of the system, fatigue is a common failure mechanism of sucker rods in service.

However, under the effect of a harsh environment, which very frequently occurs in oil wells, the correlation may no longer be valid because the presence of hydrogen sulfide (H2S), carbon dioxide (CO2), chlorides, and other compounds in aqueous solutions, can considerably reduce the fatigue life of the components.

Accordingly, corrosion is a major issue in the oil and gas industry, requiring special considerations in the selection of materials and well design.

Further, increased volumes of injection water / gas for mature fields and shale operations can increase the risk of failures related to corrosion processes.

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