Hydrogen-induced-cracking resistant and sulphide-stress-cracking resistant steel alloy

Abstract

The invention relates to a quench-and-temper steel alloy for use in casing for oil and gas wells wherein such casing is exposed to low pH environments. The steel alloy has a carbon range by weight of 0.15% to 0.35%, a manganese range by weight of 0.60% to 1.10%, a molybdenum range by weight of 0.15% to 0.65%, and a sulphur range by weight of less than 0.002%. The steel alloy has a quench-and-temper micro-structure and features precipitated spheroidal molybdenum carbides in manganese- and carbon-rich bands. The steel alloy also has, by weight, a chromium range of less than 0.50%, an aluminum range of less than or equal to 0.08% and a calcium range of less than or equal to 0.0045%.

Description

[0001] The present application is a continuation-in-part application of U.S. application Ser. No. 09 / 036,545 filed on Apr. 9, 2002, which is a continuation application of application Ser. No. 09 / 036,545 filed on Mar. 6, 1998. The '545 application is a continuation-in-part application of U.S. application Ser. No. 08 / 813,374 filed on Mar. 7, 1997. The present application incorporates by reference the entire contents of all of these parent applications.[0002] This invention relates in general to a steel alloy and more particularly to a steel alloy that resists hydrogen-induced cracking and sulfide stress cracking. This alloy is particularly suitable for use in casing for use with sour oil and gas wells. The invention also comprises casing made from such alloy.BACKGROUND TO THE INVENTION[0003] HIC and SSC are two types of hydrogen embrittlement problems of particular concern to steel casing operating in sour gas environments. HIC is a hydrogen sulfide (H.sub.2S) related hydrogen embritt...

AI Technical Summary

Problems solved by technology

Once a certain threshold pressure is exceeded, cracking occurs.

If the stepwise cracking occurs beneath the steel's surface, blistering will occur on the surface.

If the applied load is perpendicular to the elongated MnS inclusion, hydrogen induced cracks nucleated at the inclusion tips will directly lead to final rupture.

Such other structural defects include grain boundaries, carbide-ferrite interfaces, oxides, and dislocation tangles.

Oil and gas well steel casing is commonly exposed to highly acidic conditions.

Many new wells contain significant concentrations of H.sub.2S while older wells become increasingly sour over their production lifetime.

However, the casing is unable to expand due to the physi

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