ABSTRACT

High strength carbon steels typically used as oil country tubular goods can be susceptible to sulfide stress corrosion cracking (SSC) when in service in environments that contain H2S. In the last 25 years, linear-elastic fracture mechanics has been used to understand both the mechanistic aspects of this form of cracking and to quantify the susceptibility to SSC of different OCTG steel grades.

This paper presents a review on the evolution of the Double Cantilever Method (DCB) as a standard practice to assess the threshold stress intensity parameter (Kissc), evaluating the capabilities and limitations of this testing method to describe the conditions associated with crack propagation.

The review study indicates that new testing methods based on the energy required for crack propagation such as Jlc might be required to overcome the limitations of the static conditions implied in the Klc evaluation approach, which limited to linear fracture mechanics, cannot address the dynamic nature of the crack propagation and its interaction with the aggressive environment

INTRODUCTION

The sulfide stress corrosion cracking (SSC) of high strength low alloy carbon steels (HSLA), used in well completion, has been a problem of major concern for the reliable exploitation of reservoirs that produce or condense significant amounts of water together with CO2 and H2S. This environment is also known as sour media.

From an Engineering perspective, the approach to assure the integrity to the structures exposed to the sour media has been the application of adequate materials selection criteria. (1, 2) The development of the materials selection criteria is subject to both the economical context of oil and gas production and progress of the applicable state of the art. (3, 4)

The use for fracture mechanics methods for the evaluation of the crack propagation toughness of high strength low alloy carbon steels exposed to sour environments, has allowed for a better understanding on the environmental thresholds were cracking can occur.(3, 5, 6) However, the implementation of techniques commonly used for studying environmentally assisted cracking have limited applicability in the experimental context of testing in sour environments. (7-9)

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