Session: 03-03-03 Dent Modeling and API 1183 I

Paper Number: 133972

133972 - Modification of Dent-Weld Interaction Factors and Dent Corrosion-Gouge Discrimination Methodology Incorporated in API RP 1183 

Abstract: 

The presence of coincident features like welds, corrosion or gouge within a dent can have a significant impact on dent fatigue life. API RP 1183 incorporates several different approaches to consider the impact of weld, corrosion or gouge on dent integrity. The present paper discusses further development and modifications proposed to consider the dent weld interaction methodology and dent corrosion gouge discrimination approach presently incorporated in API RP 1183.

A fatigue life reduction factor of 10 is incorporated in API RP 1183 when a dent is interacting with a weld. This reduction factor was developed based on the dent fatigue full scale tests where weld was positioned at the critical location of the dent. The reduction factor of 10 is very conservative especially when a weld is located further away from the dent peak. The presence of dents in a pipe result in a large stress range gradient as we move further away from the dent peak. Therefore, the effect of the weld on the dent fatigue life should be lower as the distance of the weld from the dent peak increases. The work presented in this paper discusses the results of a project carried out on behalf of Pipeline Research Council International (PRCI), where the presence of stress range gradient within a dent was utilized to modify the dent weld reduction factor for single peak dents. Over 1,000,000 dent finite element simulations were evaluated, and their corresponding stress range gradients captured to modify the reduction factor as the location of weld moves away from the dent peak. Based on this study a range of fatigue life reduction factors ranging between 3 and 10 have been proposed depending upon the location of the weld, dent geometry, dent restraint condition and pipe geometry.

The corrosion-gouge discrimination method described in Annex H of API RP 1183, Figure H2 was developed to determine the type of metal loss (corrosion or gouge) coincident with a dent. The Annex H approach utilizes four queries regarding the dent geometry, metal loss geometry and position, and pressure condition during ILI measurement to make a determination. The Annex H approach was evaluated in this project using real-world data provided by pipeline operators that consisted of a set of field inspection listings and in-line inspection (ILI) feature listings of dents coincident with metal loss. ILI data was used in the Annex H approach to determine whether each metal loss feature was corrosion or gouge-like. Work was also carried out to implement a logistic regression model to discriminate between a gouge and a corrosion feature, which shows promise. The logistic regression model incorporated pipe outer diameter (OD), wall thickness (WT), metal loss clock position, axial and circumferential distance between dent and metal loss, metal loss aspect ratio and dent strain as input variables. The Annex H approach and the logistic regression model were tested and optimized using in ditch non-destructive evaluation (NDE) results and then implemented using ILI data. This paper presents the results based on the ILI data and the results confirmed against the field inspection reported observations.

Presenting Author: Arnav Rana BMT Canada Ltd

Presenting Author Biography: xxx

Authors:

Arnav Rana BMT Canada Ltd
Sanjay Tiku BMT Fleet Technology Limited
Aaron Dinovitzer BMT Canada Ltd
Yohann Miglis KinderMorgan
Munendra Tomar TC Energy
Mark Piazza API