Mixed-mode Ⅰ/Ⅲ crack-tip configuration identification and FAD assessment for process pressure equipment
WANG Lu
XIE Yujun
WANG Kaile
WANG Bingxue
Abstract：During service,pressure equipment is frequently subjected to complex loading conditions such as start-stop fluctuations,assembly misalignments,and bending-torsion coupling,which can readily induce mixed-mode Ⅰ/Ⅲ cracks.Variations in crack-tip configurations significantly affect the equivalent fracture toughness and consequently alter the outcomes of failure assessments.To address this issue,an integrated framework of"configuration identification-equivalent threshold-FAD assessment"is developed based on a three-dimensional energy model.Five representative crack-tip configurations including tri-branching,side-branching,symmetric branching,kinking and extension are characterized,and a unified scaling approach is employed to normalize the equival-ent fracture toughness.Furthermore,a robust statistical method incorporating the median and MAD-based dispersion,combined with a nearest-neighbor decision rule,is applied to establish an engineering pathway that extracts representative values from scattered ex-perimental data,thereby transforming uncertain inputs into reliable assessment parameters.The method is applied to eight welded de-fects in three thick-walled pressure vessels,where-20℃charpy impact tests and fracture mechanics calculations are used to obtain the corresponding equivalent fracture toughness values,which are then embedded into FAD curves for evaluation.The results indic-ate that under the conventional assessment approach,all defect evaluation points fall within the safe region,whereas the coordinates of the points obtained using the present method shift upward overall,with some approaching the failure curve,suggesting potential risks.Compared with traditional approaches,the proposed procedure provides more conservative assessment results and demon-strates higher sensitivity and safety margins for crack-like defects.It offers a traceable technical basis for the integrity evaluation of process pressure equipment under complex loading conditions.
Keywords：process pressure equipmentmixed-mode Ⅰ/Ⅲ crackcrack tip configurationsfracture toughnessfailure assessment diagramsafety assessment
Publication Date：2026-02-20
Online Publishing Date：2026-03-19(First online date of this platform, not the publication date of the document)
Pages：9( 240-248 )