Level 3 Fitness for Service Assessment of Dented Pipes With Diameter Less Than 6.25 Inch

The aim of this paper is to investigate the parameters affecting the structural integrity for piping with dents anomalies. As per the requirements to part 12 of the API 579-1/ASME FFS-1, 2016 [1], level 1 and 2 fitness for service (FFS) assessment procedures can’t be used for dented pipe with diameter less than 6.25 inch. Such small size pipes can only be assessed using level 3 assessment procedure. The pipe was indented in the FEA model with a rigid indenter. The indented pipe was then evaluated under general collapse and local failure criteria under different loading combinations using the elastic plastic analysis approach. The pipe material is defined using a multi-linear isotropic hardening model as per Annex 3-D of ASME BPVC, sec. VIII, div. 2 [2]. The effect of nominal pipe size, pipe schedule, and dent’s radius of curvature and depth on the plastic strain, and strain ratio are studied. Following Taguchi design of experiments methodology [5], a partial factorial design was adopted to allow the investigation of multiple levels value for each parameter. This analysis uses a real-life dent profile which was measured using automatic ultrasound inspection (AUT) and fitted to a spherical profile. The significance of each parameter on the different measured responses is evaluated.