Dents in buried pipelines can occur due to a number of potential causes; the pipe resting on rock, third party machinery strike, rock strikes during backfilling, amongst others. The long-term integrity of a dented pipeline segment is a complex function of a variety of parameters, including pipe geometry, indenter shape, dent depth, indenter support, pressure history at and following indentation. In order to estimate the safe remaining operational life of a dented pipeline, all of these factors must be accounted for in the analysis. The paper discusses the full-scale dent testing being completed to support the development of pipeline integrity management criteria and is a continuation of the work discussed in previous IPC papers [1,2]. The material and structural response of the pipe test segments during dent formation and pressure loading has been recorded to support numerical model development. The full scale experimental testing is being completed for pipe test specimens in the unrestrained and restrained condition using different indentation depths and indenter sizes. The dents are pressure cycled until fatigue failure in the dent. This paper presents typical data recorded during trial including indentation load/displacement curves, applied pressures, strain gauges along the axial and circumferential centerlines, as well as dent profiles. The use of the full-scale mechanical damage test data described in this paper in calibrating and validating a finite element model based integrity assessment model is outlined. The details of the integrity assessment model are described along with the level of agreement of the finite element model with the full scale trial results. Current and future applications of the integrity assessment model are described along with recommendations for further development and testing to support pipeline integrity management.

External interference on gas and oil transmission pipelines is consistently reported as leading cause of leaks in Europe and USA as identified in the EGIG and PHMSA incident databases. External interference due to ground working machinery strikes, rock strikes during backfilling, etc. on buried pipelines result mainly in dent and gouge defects. The long-term integrity of a pipeline segment damaged by a dent and gouge defect is a complex function of a variety of parameters, including pipe material properties, pipe geometry, defect geometry linked to indenter shape, aggression conditions. The complexity and extreme variability of these dent and gouge defect shapes and pipe materials lead simple assessment models to scattered predictions, hinting towards an insufficient description of real structural and material behavior. To improve knowledge beyond the numerous studies led in the past, and to provide a sound foundation for developing and validating mechanistic models for predicting burst and fatigue strength of such defects, a large experimental program was funded by PRCI and US DoT and further coordinated with a complementary EPRG program. The experimental program part dealing with combined “Dent and Gouge” defects is covered for modern pipes (24″ OD, X52 and X70) by PRCI project MD-4-1: realistically created (with a Pipe Aggression Rig) defects submitted to full scale burst and fatigue tests, in addition to extensive characterization. This work interfaces with modeling to predict the immediate burst strength and fatigue resistance of such damage in two PRCI projects denoted MD-4-3 and MD-4-4 respectively. This paper gives an overview of some of these activities: PRCI project MD-4-1 results: material characterization, full scale burst and fatigue tests on Dents with Gouges, as well as detailed explanations concerning the initial approach to model burst and fatigue life of these defects, as developed byr PRCI project MD-4-4. The final outcome of the expected knowledge improvements about the mechanical strength of dent and gouge combinations will be applicable by pipeline operators, in order to enhance integrity management systems designed to manage the threat associated with mechanical damage.

Onshore pipeline industry has deployed in the last decade comprehensive integrity management programs in a constrained environment. These programs address all types of threats and resulting defects, yet the most complex defects are those due to mechanical damage, as they can combine local pipe deformations (dents) with metal removal (gouges) or even cracks. These programs are first placed in the broader risk management perspective that justify the whole approach and provide a view of the context. Then, operational threat management programs for mechanical damage as implemented by operators are briefly described here, and serve as a basis to identify the main gaps in terms of technology and knowledge. Finally, both incremental and more game-changing innovations as produced by R&D performed by PRCI and consultants, are described in subsequent sections as possible options to fill the identified gaps. Examples of roadmaps are provided that explain the coverage in terms of existing and evolving knowledge and technology, as provided by these R&D programs, to fill these gaps. These various levels of representations are complementary tools to communicate about links between operations, R&D, and their contributions to public safety.

Pipeline dents and mechanical damage remain an integrity threat within the Oil & Gas pipeline industry. Such features typically consist of a localized deformation of the pipe wall. Under certain conditions, cracking may develop within or adjacent to the area of deformation due to stress concentration factors resulting from the deformation itself or from secondary damage such as a scrape or gouge. Conventional inline inspection technologies consistently to date have not explicitly addressed inspection capabilities for cracking within dents. This paper presents the results of a collaborative technical effort to assess and advance the abilities of EMAT inline inspection technologies to identify and characterize such mechanical damage features as found in liquid pipelines. The background and application of these advanced technologies for the targeted threats is discussed, as well as the experimental testing performed and results achieved.

Mechanical damage has been identified as a significant integrity threat within the Oil & Gas pipeline industry. In addition to deformation, associated secondary pipeline damage may also consist of coating removal, metal removal and cold working of the underlying metal that may result in cracking within the dented area. Detection of cracks within dented areas of the pipe using conventional Ultrasonic Technology (UT) and Magnetic Flux Leakage (MFL) In-line Inspection (ILI) technologies has been of limited success due to the variety of possible feature expressions, sensor design and arrangements, and the related complexity within the underlying physics for detection and characterization. Previous studies have shown the feasibility of Electro Magnetic Acoustic Transduction (EMAT) technology for detecting and characterizing crack related indications within dents on liquid pipelines. This study expands upon experimental investigations using pull through ILI tests on manufactured dents where machined linear indications (notches) were introduced into the dents. In this paper, the performance of EMAT technology for detection and characterization of crack related features in liquids pipelines under real operating conditions is presented. EMAT data were combined with high resolution caliper data, ultrasonic crack inspection data and dent strain assessment data, to demonstrate the EMAT capabilities to enhance pipeline integrity management of dents. Results of field non-destructive examinations are compared to EMAT predicted values to assess the performance of this technology. This study presents a supplementary method of detecting and mitigating coincidental crack related features with dents on liquids pipelines, further enhancing the safety and improving the integrity management of pipelines.