Effect of DCB Side Groove Geometry on KIssc Results

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Due to the increasing interest of the O&G industry on high grade tubulars working at high pressures, the assessment of operational conditions of Oil country Tubular Goods (OCTG) subjected to Sulfide Stress Cracking (SSC) is of particular importance.

AMPP adopts different test methods to evaluate material susceptibility to SSC in wet H2S environments, for which, Method D according to NACE TM0177 determines a quantitative value of material resistance using a Double Cantilever Beam (DCB) specimen that can be used for design and qualification purposes. This is a crack arrest type fracture mechanics test that can be traced back to the work of Heady in 1977 in which the material resistance to propagation of environmental cracks is expressed in terms of a critical stress intensity factor, KIssc.

Product Number: 51323-19469-SG

Author: Sebastián Cravero, Maria José Cancio, Martín Valdez, Gustavo Kissner, Pedro Olivo

Publication Date: 2023

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The objective of the present paper is to study the effect of the root radius of groove geometry on KIssc tests. Finite element analyses were used to determine the stress intensity factor and crack opening stresses ahead the crack-tip for U-groove (radius 0.95 mm) and V-groove geometries (radius 0.25, 0.50 and 0.70 mm). Method D tests on T95 and C110 materials were carried out in NACE A solution using two arm displacement: 0.5 mm and 0.71 mm. Numerical analysis showed that increasing radius would result in a non-uniform crack tip/front straightness along the specimen width and less planarity in the crack growth. In another words, the increment of side groove radius produced higher KISSC and more variability in T95 test results. Test in C110 grade were not so conclusive, but, the increment in side groove radius would lead to an increment in KIssc. Crack growth surfaces suggest that edge cracking morphology would not be directly related to side groove radius.