Application of failure assessment diagram methods to cracked straight pipes and elbows

Abstract

This paper reports fracture assessments of large-scale straight pipes and elbows of various pipe diameters and crack sizes. The assessments estimate the load for ductile fracture initiation using the failure assessment diagram method. Recent solutions in the literature for stress intensity factor and limit load provide the analysis inputs. An assessment of constraint effects is also performed using recent solutions for elastic T-stress. It is found that predictions of initiation load are close to the experimental values for straight pipes under pure bending. For elbows, there is generally increased conservatism in the sense that the experimental loads are greater than those predicted. The effects of constraint are found not to be a major contributor to the initiation fracture assessments but may have some influence on the ductile crack extension.

Application of Failure Assessment Diagram (FAD) for Steel Welded Connection Based on BS7910 and DNV-RP-108

“…The results show that the assessment points for the predicted loads lie on the failure assessment curve. It can be seen that the predicted initiation loads are close to the experimental loads, with the percentage differences and that ductile initiation occurs before plastic collapse [10].…”

“…Fig. 3 and 4 show that the assessment points (Lr, Kr) for the 13 elbows under opening mode (crack at extrados) and closing bending (crack at intrados) evaluated at the experimental and predicted initiation loads, plotted on the FAD [10]. Predicted and experimental initiation load points (∆a=0.2 mm) on FAD under opening mode [10].…”

“…Option 2: is based on the use of a material-specific stressstrain curve. Predicted and experimental initiation load points (∆a=0.2 mm) on FAD under closing mode [10]. Option 3: uses numerical analysis to generate a FAD and is not confined to use materials showing ductile tearing [12].…”

“…Fig.4Circumferentially through-wall cracked elbows under closing mode.Predicted and experimental initiation load points (∆a=0.2 mm) on FAD under closing mode[10].…”

‘Mind the gap’ in fitness-for-service assessment procedures-review and summary of a recent workshop

“…One of the difficulties with the approach described above is that a number of different specimens or defect sizes are required at step 5 in order to generate the function of step 6, which is used to construct the constraint modified FAD. More recently, therefore, alternative approaches have been suggested [8,9], which are targeted at the use of specimens which more closely match the specific constraint level of interest in the component being assessed. The steps in an alternative constraint approach are as follows.…”