Rodolfo F. de Souza

Revised η-Factors andJ-CTOD Relationships for SE(B) Fracture Specimens Including 3D Effects and Implications for Fracture Toughness Measurements

This work provides revised η-factors derived from CMOD records and J-CTOD relationships applicable to estimate the J-integral and CTOD in SE(B) specimens with varying crack size and specimen configuration. Very detailed non-linear finite element analyses for plane-strain and 3D models provide the evolution of load with increased crack mouth opening displacement, which is required for the estimation procedure. The analysis matrix considers SE(B) specimens with W=2B and W=B configurations with and without side grooves covering a wide range of specimen thickness, including a precracked Charpy (PCVN) specimen. Overall, the present results provide validation of the J and CTOD evaluation procedure currently adopted by ASTM E1820-11, while at the same time giving improved estimation equations for J and CTOD incorporating 3D effects which enter directly into more accurate testing protocols for experimental measurements of fracture toughness values using 3P SE(B) specimens.

Fitness-for-Service Fracture Assessments of Dissimilar Pipe Girth Welds Incorporating New Crack Driving Force Solutions

The increasing demand for energy and natural resources has spurred a flurry of exploration and production activities of oil and natural gas in more hostile environments, including very deep water offshore production. Currently, structural integrity of submarine risers and flowlines conducting corrosive and aggressive hydrocarbons represents a key factor in operational safety of subsea pipelines. Advances in existing technologies favor the use of CMn steel pipelines (for example, API X65 grade steel) clad or mechanically lined with a corrosion resistant alloy (CRA), such as Alloy 625, for the transport of corrosive fluids. This work focuses on a fitness-for-service defect assessment procedure for strength mismatched welded components incorporating new crack driving force and limit load solutions. The study broadens the applicability of current evaluation procedures for J and CTOD which enter directly into structural integrity analyses and flaw tolerance criteria to provide a fairly comprehensive body of numerical solutions for crack driving forces in mismatched girth welds with circumferential surface cracks. This investigation also provides mismatch yield load solutions which are central to accurately predict failure load in strength mismatched structures subjected to large scale plasticity and ductile behavior. An approach is utilized to analyze the potential effects of the undermatching girth weld on critical flaw sizes for a typical lined pipe employed in subsea flowlines having a girth weld made of Alloy 625.Copyright

An Evaluation Procedure for Crack Driving Forces in Mismatched Welds and its Applicability to ECA Analysis of Undermatched Clad Pipe Girth Welds

Structural integrity of submarine risers and flow lines transporting corrosive and aggressive hydrocarbons represents a key factor in operational safety of subsea pipelines. Advances in existing technologies favor the use of C-Mn steel pipelines (for example, API X65 grade steel) either clad or mechanically lined with a corrosion resistant alloy (CRA), such as Alloy 625, for the transport of corrosive hydrocarbons. However, while cost effective, specification of critical flaw sizes for their girth welds become more complex due to the dissimilar nature of these materials. In particular, effective fracture assessments of undermatched girth welds remain essential to determine more accurate acceptable flaw sizes for the piping system based upon engineering critical assessment (ECA) procedures. This work focuses on development of an evaluation procedure for the elastic-plastic crack driving force (as characterized by the J-integral) in pipeline girth welds with circumferential surface cracks subjected to bending load for a wide range of crack geometries and weld mismatch levels based upon the GE-EPRI framework. The study also addresses the effects of an undermatching girth weld on critical flaw sizes for a typical clad pipe employed in subsea flowlines having an Alloy 625 girth weld. The extensive 3-D numerical analyses provide a large set of solutions for J in cracked pipes and cylinders with mismatched girth welds while, at the same time, gaining additional understanding of the applicability of ECA procedures in welded cracked structural components.Copyright

Revised η-Factors for 3P SE(B) Fracture Specimens Incorporating 3-D Effects

Standardized procedures to measure cleavage fracture toughness of ferritic steels in the DBT region most commonly employ three-point bend fracture specimens, conventionally termed SE(B) or SENB specimens. The evaluation protocol of fracture toughness for these crack configurations builds upon laboratory records of load and crack mouth opening displacement (CMOD) to relate plastic work with J (or, equivalently, CTOD). The experimental approach employs a plastic η-factor to relate the macroscale crack driving force to the area under the load versus crack mouth opening displacement for cracked configurations. This work provides revised η-factors derived from CMOD records applicable to estimate the J-integral and CTOD in SE(B) specimens with varying crack size and specimen configuration. Non-linear finite element analyses for plane-strain and 3-D models provide the evolution of load with increased CMOD which is required for the estimation procedure. The analysis matrix considers SE(B) specimens with W = 2B and W = B configurations with and without side grooves covering a wide range of specimen thickness, including precracked Charpy (PCVN) specimens. Overall, the present results provide further validation of the J and CTOD evaluation procedure currently adopted by ASTM 1820 while, at the same time, giving improved estimation equations for J incorporating 3-D effects which enter directly into more accurate testing protocols for experimental measurements of fracture toughness values using 3P SE(B) specimens.Copyright