ABSTRACT

The double-cantilever beam (DCB) test method standardized in ANSI NACE TM0177 is increasingly being applied as a quality assurance test to specify the performance of carbon and low-alloy steels for sour service. The DCB test can contribute to the quantitative evaluation of fracture toughness in a specific environment by assessing the crack arrest of a pre-cracked specimen. The test method has been modified and specified tightly from the viewpoint of specimen geometry, test environment, and initial stress intensity factor controlled by arm displacement to obtain highly repeatable test results. In this paper, the influence of various side-groove root configurations on KISSC and finite-element analysis (FEA) results were focused upon because different types of V-notched side-groove roots are considered to change the stress concentration at the bottom of the side-groove and therefore affect the incidence of edge crack occurrence in the DCB test. On the contrary, the KISSC value remains unchanged because the K value of different types of V-notched side-groove configurations at the middle of specimen thickness is the same as a standard DCB test specimen. Decreasing the incidence of edge cracking with increasing V-notched side-groove root is discussed from the viewpoint of fracture mechanics.

INTRODUCTION

The resistance of low-alloy steels oil country tubular goods (OCTG) to sulfide stress cracking (SSC) is an important issue regarding material selection. The NACE TM0177-20161 standard describes several test methods to be used to assess the susceptibility of steels during initiation and propagation of SSC.

To determine the fracture toughness in a sour environment, described as Klssc, the NACE TM0177 Method D (double-cantilever beam (DCB)) test method1, which was first proposed by Heady2, is increasingly applied as a quality control test for OCTG. The KI equation for the present DCB specimen in the TM0177 was experimentally observed to follow a modified version as given in Equation (1).

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