Mures Zarea

EPRG Tier 2 Guidelines for the Assessment of Defects in Transmission Pipeline Girth Welds

This paper presents the proposed revisions of the EPRG guidelines for the assessment of defects in transmission pipeline girth welds. The revisions cover Tier 2 of the guidelines, in particular (a) the extension of the guidelines to include Grade L555 (X80) material, (b) the assessment of surface-breaking defects with heights up to 5mm and (c) the assessment of multiple co-planar defects. Since the welds should be, at least, matching the pipe material in yield strength, the paper also defines the required levels of weld metal yield strength for the safe application of the guidelines.

Experimental Investigation on Combined “Dent and Gouge” Defects on Vintage Steel Transmission Pipelines

Mechanical Damage on pipelines is the most frequent in service failure cause, at least in Europe. The category of Mechanical Damage actually covers on one hand rock dents, on the other hand, combined “Dent and Gouge” defects resulting from an impact by a ground moving machinery. The latter are complex defects in terms of geometry and mechanical behavior. Improved understanding of toughness reduction in these defects and their vicinity, especially in the case of vintage pipelines, and its impact on burst pressure and remaining fatigue lifetime is crucial in order to ensure a high safety level at the best economic conditions for transmission pipelines. PRCI and DOT/PHMSA supported a large experimental program to investigate the burst and fatigue strength of such defects in modern pipes as well as in vintage pipes by producing very detailed reference experimental data in order to support improvement of current burst and fatigue strength models for these defects.This paper focuses on experimental results data for two vintage pipes removed from service, one 26″ in diameter, X52 grade (from US) with high carbon content and sulfur content involving very low toughness and another 24″ in diameter, X63 grade (from Europe) characterized by alternated pearlite and ferrite bands. In each pipe, two different types of combined “Dent and Gouge” defects were created, “shallow dent with shallow gouge” and “severe dent with moderate gouge”. Each defect was reproduced three times:• One for destructive metallurgical investigation;• A second one for highly instrumented burst test;• A third one for highly instrumented fatigue test.The defect profile was monitored during pressure increase until burst, and a camera recorded pictures at each fatigue cycle to detect crack initiation at the gouge bottom and its further propagation. The different features of the experimental work and results described in this paper are:• Material characterization;• Metallurgical and residual stress investigation on combined dent and gouge defects;• Burst tests conditions and results;• Fatigue tests conditions and results.• Comparison with results from modern pipes containing the same types of defects.All this experimental data is made available for an in-depth understanding of the “Dent and Gouge” type defects leading to improved models, as well as reference data for validating these improved models for burst and fatigue strength of these defects.Copyright

Neutron Diffraction Studies of Residual Stresses Around Gouges and Gouged Dents

The residual stress pattern surrounding gouges is complex and, to date, has not been accurately modeled using stress modeling software. Thus measurement of these stress distributions is necessary. Neutron diffraction is the only experimental method with the capability of directly evaluating residual strain throughout the entire thickness of a pipe wall, in and around dent or gouged regions.Neutron diffraction measurements were conducted at the NIST reactor on three gouged dents in X52 pipeline sections. These were part of a larger sample set examined as part of the comprehensive MD4-1 PRCI/DOT PHMSA project. Gouges contained in pipeline sections were termed BEA161 (primarily a gouge with little denting), and BEA178 (mild gouging, very large dent). Measurements were also conducted on a coupon sample – P22, that was created as part of an earlier study.For the moderate gouges with little or no associated denting (BEA161 and P22) the residual stress field was highly localized around the immediate gouge vicinity (except where there was some denting present). The through wall stress distributions were similar at most locations — characterized by neutral or moderate hoop and axial stresses (50–100MPa) at the outer wall surface (i.e. at the gouge itself) gradually becoming highly compressive (up to −600MPa) at the inner wall surface. The other sample (BEA178) exhibited a very mild gouge with significant denting, and the results were very different. The denting process associated with this kind of gouge+dent dominated the residual stresses, making the residual stress distribution very complex. In addition, rather than having a residual stress field that is localized in the immediate gouge vicinity, the varying stress distribution extends to the edge of the dented region..Copyright

Extension of Current Defect Assessment Methods for Gouge and Corrosion Defects in X80 Grade Pipeline

The increasing demand for natural gas affects the type of transportation, both from the strategic and the economic point of view. Long-distance pipelines are a safe and economic way to transport the gas from production sites to end users. Hence, pipes producers need to supply the market executing projects where high strength material is involved, to reduce the steel use.Among high strength steel grade pipes (X80 - X100 - X120), the X80 grade is already in use for a number of gas pipelines in the world since many years.There is a need to evaluate the suitability of extending the current Fitness For Purpose methods to X80 grade steel linepipe, since the existing guidance was developed and validated mainly on test data coming from steel pipes of grade lower than X80. Hence they could not be directly applied to X80 grade pipes, but should be experimentally verified, otherwise their straightforward extrapolation would be questionable.EPRG recognized the need to cover this gap and launched a specific project, aimed at verifying the applicability of the presently available criteria to X80 grade, with particular focus on corrosion and gouge types of defects, longitudinally oriented.The project includes the collection and review of available tests data and FFP criteria, and the identification of the most promising among those collected. Four hydraulic full scale burst tests on X80 representative pipes (helically and longitudinally welded) containing simulated corrosion and gouge defects have been carried out to experimentally verify the applicability of the criteria to the X80 grade pipes.The selected criteria for the corrosion (DNV RP-F101) and for the gouge (Battelle NG-18) defects revealed to be suitable for X80 grade pipes too, as demonstrated by the accuracy in predicting the failure pressure of the experimental tests and of the literature database. The criteria showed to be even more accurate for X80 grade than they were for lower grades.Finally, it is worth mentioning that the selected criteria did not need any correction factor for obtaining the best prediction. Such a result is a demonstration of the sound theory behind the criteria.Copyright

Measuring the Effectiveness of Damage Prevention Techniques and Defining the Key Performance Indicators on Damage Prevention Efficiency

Pipeline operators expend substantial efforts to develop, implement, and audit their Public Awareness and Pipeline Damage Prevention Programs. While the rate of pipeline damage incidents from third-party and outside force impacts has progressively declined over a period of several decades, these events remain a high priority for the pipeline industry and external stakeholders.There are multiple management and communications tools that are used to support Damage Prevention programs for energy transmission pipeline operations. These tools are applied to large pipeline systems that cross a range of geographic, population, and regulatory boundaries. These factors make it challenging to determine the effectiveness of the individual tools applied for damage prevention for energy transmission pipeline systems.This paper present the results of research performed through Pipeline Research Council International, Inc. (PRCI) to measure and quantify the effectiveness of the various damage prevention tools and techniques as they apply to energy transmission pipeline systems. The project focuses on data collection through a web-based platform to provide the basis to establish a set of Key Performance Indicators (KPIs) for assessing the effectiveness of the methods and techniques that are used as standard practices by most pipeline operators in their damage prevention programs. The research includes development of a consistent and systematic process and database for collecting information on damage and “near hit” incidents that are recorded by pipeline operators. Fault-tree analysis of these data is expected to show where improvements can be made (e.g., one-call center, ticket handling, operator response, contractor cooperation and diligence, locating and marking, monitoring). Improvements will be measured by PRCI by capturing and analyzing the data over a multi-year period.The key output of the project will be metrics that demonstrate which damage prevention activities are more effective in reducing impacts and “near hits” to pipelines and which activities positively contribute to the safe operations of the pipeline system.Copyright

Review of R&D in Support of Mechanical Damage Threat Management in Onshore Transmission Pipeline Operations

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.Copyright

Full Scale Experimental Database of Dent and Gouge Defects to Improve Burst and Fatigue Strength Models of Pipelines

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.Copyright