ABSTRACT

The susceptibility of a high strength low alloy nanostructured steel to sulfide stress corrosion cracking (SSCC) resistance is assessed. Notch Tensile Slow Strain Rate Testing (NTSSRT) method is used to evaluate the threshold stress intensity values (Kisscc). The objective of this study is to understand the effect of the microstructure and chemical composition on the susceptibility to SSC; the control condition is a conventional low alloy carbon steel with a tempered martensitic microstructure.

The tests were performed in a brine with 1% NaCl buffered at pH 4.5 with H2S gas with 1% to 100% (mol %) balance N2 at room conditions. The results of the Kissc testing indicates that the nano-structured steel exhibits a value of 46 MPa m0.5 at 100% (mol%) H2S at room conditions. The same tests performed on API C110 grade steel shows 20 MPa m0.5. The evaluation of the relative crack propagation energy suggest that the nano-structured steel exhibits a much lower susceptibility to SSC than the tempered martensitic microstructure.

INTRODUCTION

Hydrogen embrittlement cracking (HEC), continues to be a significant concern for many major industries [1-4]. In the oil & gas industry, one of the more severe forms of environmentally assisted cracking found is the sulfide stress corrosion cracking (SSC), in which H2S contained in sour environments, mediates to enhance the uptake and permeated hydrogen which plays an important role in the crack initiation and propagation [3, 5-7].

The susceptibility to SSC depends on the microstructural characteristics of the material. In materials, such as carbon steels martensitic structures product of heat treatment such as quenching are typically found to be more susceptible to SSC [8-10]. Hence, the focus of the development of SSC resistant high strength steels has been the control of the microstructural features [10-13].

The objective of the present study is to evaluate the susceptibility of a novel high strength low alloy nanostructured steel to sulfide cracking resistance (SSC). The relative effect of the steel structure on the susceptibility to SSC is studied by comparing with a control condition, which is a conventional low alloy carbon steel with a tempered martensitic microstructure.

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