A New Methodology for CTOD Estimation Using Double Clip Gauge in Pipeline Steels

The increasing energy demand has spurred the exploration and production of oil and natural gas in dangerous and hostiles areas. Therefore, accurate calculation of fracture toughness is essential for fitness-for-service (FFS) analyses of critical engineering structures, such as the piping system used in the offshore industry. Regarding the oil and gas exploration in Brazil, 68% of the total area has already been explored, with 71% of that explored area having been developed in recent years. Oil and gas companies have preferentially chosen Crack-tip Opening Displacement (CTOD) due to the vast data of fracture toughness obtained in the past. Moreover, the professionals involved in this area are more familiarly with this parameter since it is easy of understanding because it involves physically crack flank deformation. Different methods to measure CTOD are available in the literature, such as the plastic hinge model, J-integral conversion and double clip gage method (DCGM). Experimentally, DCGM has been widely used to calculate in offshore pipelines. Discrepancies between experimental and numerical measures have been reported. Motivated by the explanation above, this work aims to propose new numerical analyses to evaluate the CTOD using the DCGM using non-linear finite element analyses. New and improved equations are developed to take into accounting knifes position.