bluuebunny/crossref_metadata_2025 huggingface dataset:
Runaway Instability of Pump-Turbines in S-Shaped Regions Considering Water Compressibility
Authors: Zeng Wei , Yang Jiandong , Guo Wencheng
Published: December 2014

Pump-turbine characteristics greatly affect the operational stability of pumped-storage plants. In particular, the S-shaped region of the characteristic curves leads to severe instability during runaway conditions with servomotor failure. Thus, this paper aims to investigate the runaway stability criterion by considering all of the important effects in the hydromechanical system. The criterion also helps to judge the S-characteristics of pump-turbines and can provide a guide for plant design and turbine optimization. First, the pump-turbine characteristic curves are locally linearized to obtain formulae for the relative changes of discharge and torque, which depend on the relative changes of rotational speed and water head. Control theory is then applied to analyze the high-order system, by importing the transfer function of the conduits in the elastic mode. Two different kinds of oscillation are found, associated with water inertia and elasticity, based on the established theoretical mathematical model. New stability criteria for the inertia wave in both rigid and elastic modes are developed and compared. The comparison reveals the effect of the water elasticity on runaway instability, which has often been neglected in the previous work. Other effects, such as friction loss and the timescales of water flow and machinery, are also discussed. Furthermore, the elastic wave, which often has a higher frequency than the inertia wave, is also studied. The stability criterion is deduced with analyses of its effects. Based on the stability criteria for the inertia wave and elastic wave, the unstable regions for two waves of the S-shaped curves are plotted. The results are applied to explain the development from inertia wave to elastic wave during transient behavior at runaway conditions. Model tests of runaway conditions were conducted on a model pumped storage station and the experimental data show good agreement with the theoretical analyses regarding the instability of the inertia wave. Further analyses and validations are made based on transient simulations. The simulation software topsys, which uses the method of characteristics (MOC) and a unit boundary represented by a spatial pump-turbine characteristic surface, was applied to analyze the elastic wave. This also supports the conclusions of the theoretical research.
Evaluation of Maximum Velocity Limit Criteria in High Pressure Natural Gas Systems
Authors: Hartloper C. , Botros K. K. , Jensen L. , Tse A.
Published: December 2014

In the gas transmission industry, standards such as API 14E, IGEM/TD/1 and IGEM/TD/13 limit the maximum velocity through existing pipeline and measurement facilities. However, in these standards it is unclear what the consequences of exceeding the velocity limits are. In this paper, six potential velocity limiting factors were identified: pressure loss, flow generated pulsations, pipe-wall erosion, audible noise, acoustic-noise-induced fatigue and filtration/separation equipment. These six factors were evaluated in the context of velocity increases through a case study meter station on the TransCanada pipeline in Ontario. It is found that, generally, side-branch generated pulsations and audible noise are the most limiting factors to increases in velocity, while the pressure loss across the meter station and filtration/separation equipment compatibility should be considered when increasing gas velocity. Pipe-wall erosion and acoustic-noise-induced fatigue should not be a concern when increasing the gas velocity, particularly for typical natural gas that complies with applicable pipeline specifications. For the case study meter station in its normal operating configuration, increases up to two times the current highest flow rate through the meter station show no major concerns, even though the gas velocity exceeds the limits imposed by the above-mentioned standards at most locations throughout the meter station.
Validating ILI Accuracy Using API 1163
Authors: Smart Lucinda , Haines Harvey
Published: December 2014

It is important to validate the accuracy of in-line inspection (ILI) tools to know how many excavations are needed to maintain the integrity of a pipeline segment. Performing sufficient excavations is important to ensure there are no defects left in the pipeline that have even a remote chance of failure. In some cases additional excavations may be necessary to ensure safety where in other cases no excavations may be necessary. This paper looks at using spatially recorded metal-loss data collected “in-the-ditch” to measure the accuracy of ILI tool results. Examples of spatial in-ditch data are laser scans for external corrosion and UT scans for internal corrosion. Spatially mapped metal loss, because all of the corrosion area is mapped, has the advantage of allowing more comparisons to be made for a given corrosion area and also allows the interaction among corrosion pits to be studied for examining burst pressure calculation accuracy. From our studies we find the depth error for shallow corrosion 10%–20% wt deep is often not representative of deeper corrosion in the same pipeline and the interaction criteria for ILI tools needs to be larger than the interaction criteria for in-ditch data. Examples are shown with these types of results, and by interpreting the results in conjunction with API 1163, certain ILI runs are shown that require no excavations where others may require additional excavations than suggested by normal +/−10% wt ILI data.
Impact of Welding Parameters on Weld Seam Properties of Seamless X80 Linepipe Steel Grade
Authors: Bruns Claas , Wiebe Jörg , Niklasch Dorothee , Mahn Denise , Schmidt Tanja
Published: December 2014

The challenging exploration conditions appearing in ultra deep offshore projects promoted the development of high strength linepipe steel grades with yield strength of 80 ksi and higher in recent years. With increasing strength more attention has to be paid to welding procedures to realise the required mechanical properties of the weld seam. The combination of demanding toughness requirements at low temperatures and adequate corrosion resistance of welded joints is a key for complex deep offshore riser and linepipe applications. The welding process was optimised by Vallourec with respect to heat input and preheating temperature for joining seamless quenched and tempered pipes in grade X80. A root welding strategy has been developed particularly with regards to sour service applications. Extensive mechanical test results including Charpy impact testing, hardness, CTOD and SSC testing will be presented. In addition Gleeble trials were carried out using different thermal cycles to simulate multilayer welding. The aim was to improve the understanding of the base material behaviour in the heat affected zone (HAZ) during welding. The microstructure was characterized by LOM, SEM and furthermore hardness and Charpy impact tests were executed. Based on the gathered knowledge and test results welding recommendations and welding strategies for high strength steel X80 seamless line pipes are deduced.
Effect of Dent Depth on the Burst Pressure of NPS30 X70 Pipes With Dent-Crack Defect
Authors: Ghaednia Hossein , Das Sreekanta , Wang Rick , Kania Richard
Published: December 2014

Pipeline is the common mode for transporting oil, gas, and various petroleum products. Buried linepipe can be exposed to various external interferences and corrosive environment and as a result, damage in the form of dent or corrosion or crack or gouge or combination of any of these damages can form in the pipe wall. Such damage or combined damages can reduce the pressure capacity of the pipeline. A defect combining dent and crack, often known as dent-crack defect, can develop in the wall of a buried oil and gas linepipe. This combined defect may lead to a leak or a rupture in the pipe wall and hence, the pipeline operator becomes concerned about the performance and safety of the pipeline when a dent-crack defect is detected in the field pipeline. A long-term research program is currently underway at the Centre for Engineering Research in Pipelines, University of Windsor to study the influence of various parameters such as dent depth and operating line pressure on the pressure capacity or burst strength of 30 inch diameter and X70 grade pipes with D/t of about 90. From the study completed so far, it has been found that the dent depth of 8% with crack depth of 4 mm or more can reduce the pressure capacity by 32%. This paper discusses the test specimens, test setup, test procedure, test results, and data obtained from finite element analyses.
Case Study for Releasing Stuck Pig in Non-Metallic Pipeline
Authors: Al-Khaledi Abdullah , Al-Zuwayer Hamad , Al-Ghanem Fahad
Published: December 2014

This paper discusses a case study regarding a stuck pig in a non-metallic pipeline used for effluent water service. The line was pigged and half way through the operation, the pig got stuck in the pipeline. The exact location of the pig was not known and huge sludge volume was recovered at the receiving station. Several attempts were made to release the stuck pig; these attempts were constrained by the nature of the non-metallic pipeline and its design. Through collaboration with the downstream section of Kuwait Oil Company, we were able to free the stuck pig and continue the pigging operation. Ideas that were considered and implemented to free the pig will be shared and the method chosen and implemented.
The Effect of Shallow Cracks on the Predicted Failure Pressure of Natural Gas Pipelines Containing Stress-Corrosion Cracks
Authors: Fessler Raymond R. , Rapp Steve C.
Published: December 2014

Predicting the failure pressure from the dimensions of a defect in a pipe is a critical step in direct assessment and in-line inspection. There are reasonably accurate methods for regularly shaped defects, but predicting the failure pressure for stress-corrosion cracks is more difficult because of the irregular crack front and the existence of shallow cracks or shallow extensions of deeper cracks. This paper addresses the issue of shallow cracks. This is particularly important in the case of a very shallow crack that is long enough to be classified as Category 1, but is so shallow that is does not affect the strength of the pipe. It is common practice to assume that a Category 2 crack exists some place in that segment, and a hydrostatic test would be required, although such drastic action should not be necessary because of the negligible effects on the strength of the pipe. It has been suggested that grinding 10% of the wall thickness might be a useful way to define the effective length of cracks or cracks that have shallow extensions. The effect of removing shallow cracks by grinding was investigated by analyzing twenty-five cases for which the crack profile was known. The effect depends on how the crack depth profile is characterized and whether there is a neighboring crack nearby that might interact with the flaw of interest. It was found that grinding 10% off the wall thickness will affect a small percentage of the flaws (five of the twenty-five). For those that it does affect, if the crack depth is taken as the maximum depth, the predicted failure pressure (PFP) will be very conservative, and eliminating the shallow cracks will always make the PFP less conservative, but still more conservative than desired. If this method is used, decreasing the severity category by one should be considered.
Integration of Laser Surface Scanning and Non-Linear Finite Element Analysis for the Assessment of Volumetric Corrosion in Pipeline Fittings
Authors: Andrews Robert M. , Hadden Matthew , Casson Paul , Kashap Tamsin , Johnstone Steven A.
Published: December 2014

Methods for assessing volumetric corrosion in fittings such as bends or branch connections are not well developed, although limited guidance is given in some codes. For other components and cases where the corrosion profile is complex or there are large external loads, these methods cannot be applied. In addition, detailed analysis of the actual corrosion shape and the applied loads may demonstrate significant additional margins compared with the code method. To do this, the actual profile of the corroded shape is required. This paper reports an initial study investigating methods of non-contact scanning a corroded fitting, constructing a finite element (FE) model of the corroded shape and prediction of the failure pressure.

Two corroded welded branch connections which had been removed from a block valve installation were used. The surface profiles were measured using a laser scanner and the scans imported into a FE model generation system and detailed models of the damaged connections then developed. Non-linear analyses were carried out to predict the failure pressure using assumed and measured stress-strain curves. Failure was predicted to occur in the area of the weld between the forged connection and the header.

Hydrostatic burst tests were carried out on the connections. In both tests failure initiated in the header pipe remote from the branch and the corroded area, and as a result the failure pressures were below those predicted by the FEA. However, the failures did occur at pressures about 20% higher than the original hydrostatic test pressure. Strain gauge data from the pressure tests were in reasonable agreement with the numerical predictions. Large strains were predicted and measured in the large artificial defect introduced in the second test.

This program has demonstrated the feasibility of making detailed surface profile measurements of corroded components on site, and then using these profiles in a non-linear FEA to predict failure pressures. The development work needed for routine application is discussed, and the selection of a failure criterion for the FEA when analysing complex geometries where there may be substantial through wall bending is also considered.
Control of Weld HAZ Properties in Modern High Strength Pipeline Steels
Authors: Barbaro Frank , Kuzmikova Lenka , Zhu Zhixiong , Li Huijun
Published: December 2014

Critical performance of modern high strength linepipe is related to the ability of the steel to maintain mechanical properties in the weld heat affected zone (HAZ). The region most susceptible to mechanical property degradation is the coarse grained HAZ, however in multipass welds, the intercritically reheated CGHAZ (ICCGHAZ) also presents challenges to maintain toughness.

Currently Ti is employed to minimise austenite grain coarsening through the grain boundary pinning action of TiN precipitates. This is effective because of the high thermal stability of TiN but control of the precipitate size distribution is very much dependent on alloy design and processing conditions to ensure final weld HAZ properties, particularly toughness. This can be difficult to maintain and alternative methods are required to further improve performance of the weldments.

It is now evident that increased additions of Nb in modern high temperature processed (HTP) steels have demonstrated increased control of HAZ microstructures with improved fracture toughness [1, 2]. The present paper details the microstructure - property relationship of two pipe steel grades with different alloy designs. Evaluation of the critical CGHAZ was achieved by simulation techniques, calibrated using real weld thermal cycles, to determine the influence of alloy design and specifically level of Nb on weld zone properties.

The results reveal that the fracture toughness of the simulated CGHAZ in the HTP steel is superior to that of a conventional microalloyed pipeline steel grade. Toughness was related to the distribution of martensite-austenite (M-A) constituent and the effective grain size which appeared to correspond to prior austenite grain size as evidenced by examination of cleavage facet size (CFS) on fractured Charpy specimens.
Review of Fracture Control Technology for Gas Transmission Pipelines
Authors: Zhu Xian-Kui
Published: December 2014

A fracture control plan is often required for a gas transmission pipeline in the structural design and safe operation. Fracture control involves technologies to control brittle and ductile fracture initiation, as well as brittle and ductile fracture propagation for gas pipelines, as reviewed in this paper. The approaches developed forty years ago for the fracture initiation controls remain in use today, with limited improvements. In contrast, the approaches developed for the ductile fracture propagation control has not worked for today’s pipeline steels. Extensive efforts have been made to this topic, but new technology still needs to be developed for modern high-strength pipeline steels. Thus, this is the central to be reviewed.

In order to control ductile fracture propagation, Battelle in the 1970s developed a two-curve model (BTCM) to determine arrest toughness for gas pipeline steels in terms of Charpy vee-notched (CVN) impact energy. Practice showed that the BTCM is viable for pipeline grades X65 and below, but issues emerged for higher grades. Thus, different corrections to improve the BTCM and alternative methods have been proposed over the years. This includes the CVN energy-based corrections, the drop-weight tear test (DWTT) energy-based correlations, the crack-tip opening angle (CTOA) criteria, and finite element methods. These approaches are reviewed and discussed in this paper, as well as the newest technology developed to determine fracture arrest toughness for high-strength pipeline steels.
Advancements in the Detection and Sizing of “Pinhole” Metal Loss
Authors: Santamaria Wilson , Bluck Martin
Published: December 2014

At IPC 2010 PII Pipeline Solutions (PII) presented the paper “VALIDATION OF LATEST GENERATION MFL IN-LINE INSPECTION TECHNOLOGY LEADS TO IMPROVED DETECTION AND SIZING SPECIFICATION FOR PINHOLES, PITTING, AXIAL GROOVING AND AXIAL SLOTTING”1, IPC 2010-31124. The suggestion was that this improvement would allow operators to make more informed pipeline integrity decisions in future.

In the 4 years since this paper was presented many hundreds of runs have been completed with this latest generation MFL ILI technology, capturing information on tens of thousands of kilometers of pipe, and generating a significant volume of dig verification data. In collaboration with Oil & Gas pipeline operators around the world this growing dig verification database has been utilized to improve software models, algorithms, & analysis processes to validate and further enhance system detection, sizing, & reporting capabilities.

This paper focuses on the recent collaboration between ExxonMobil and PII, to investigate system capabilities with respect to “Pinholes”, to address a known threat to a specific pipeline in the United Kingdom. This paper will describe the:

• Evolution of the “Pinhole” specification that captured the interest of ExxonMobil.

• Use of Finite Element models to predict entitlement for characterization of “Pinhole” type defects

• Detail of and results from the ExxonMobil sponsored test program that was conducted in early 2013

• The in-line inspection, analysis report, and dig verification that followed for the pipeline in question.

This joint paper, prepared and presented in collaboration by ExxonMobil & PII, will reflect the perspective and synergy of the Pipeline Owner/Operator and the ILI Vendor.
Design of Pipeline Composite Repairs: From Lab Scale Tests to FEA and Full Scale Testing
Authors: Her Remy , Renard Jacques , Gaffard Vincent , Favry Yves , Wiet Paul
Published: December 2014

Composite repair systems are used for many years to restore locally the pipe strength where it has been affected by damage such as wall thickness reduction due to corrosion, dent, lamination or cracks.

Composite repair systems are commonly qualified, designed and installed according to ASME PCC2 code or ISO 24817 standard requirements. In both of these codes, the Maximum Allowable Working Pressure (MAWP) of the damaged section must be determined to design the composite repair. To do so, codes such as ASME B31G for example for corrosion, are used. The composite repair systems is designed to “bridge the gap” between the MAWP of the damaged pipe and the original design pressure.

The main weakness of available approaches is their applicability to combined loading conditions and various types of defects. The objective of this work is to set-up a “universal” methodology to design the composite repair by finite element calculations with directly taking into consideration the loading conditions and the influence of the defect on pipe strength (whatever its geometry and type).

First a program of mechanical tests is defined to allow determining all the composite properties necessary to run the finite elements calculations. It consists in compression and tensile tests in various directions to account for the composite anisotropy and of Arcan tests to determine steel to composite interface behaviors in tension and shear. In parallel, a full scale burst test is performed on a repaired pipe section where a local wall thinning is previously machined. For this test, the composite repair was designed according to ISO 24817.

Then, a finite element model integrating damaged pipe and composite repair system is built. It allowed simulating the test, comparing the results with experiments and validating damage models implemented to capture the various possible types of failures. In addition, sensitivity analysis considering composite properties variations evidenced by experiments are run.

The composite behavior considered in this study is not time dependent. No degradation of the composite material strength due to ageing is taking into account. The roadmap for the next steps of this work is to clearly identify the ageing mechanisms, to perform tests in relevant conditions and to introduce ageing effects in the design process (and in particular in the composite constitutive laws).
Guidelines for Interpretation and Application of API Standard 1104
Authors: Bruce William A. , Amend Bill , Rogers Geoff , Wang Yong-Yi , Rapp Steve
Published: December 2014

The application of requirements contained in many industry codes and standards requires some interpretation by the user and by the regulator who is called upon to enforce their use. There are often differences in the way requirements are interpreted because of ambiguous specification language, unclear rationale behind the requirements, or novel or non-traditional applications. Some industry codes and standards contain guidance in the form of commentary sections or companion documents to assist in matters of interpretation and application. Until recently, this was not the case for API Standard 1104 – Welding of Pipelines and Related Facilities,(1) where requests for interpretation have been frequent because of unclear requirements or an absence of information pertaining to rationale.

This paper describes a project sponsored by Pipeline Research Council International (PRCI) and carried out by DNV GL that resulted in the development of a guidance document for API 1104.(2)
A Spatial Multi-Criteria Analysis Process to Optimize and Better Defend the Pipeline Route Selection Process
Authors: Seel Kevin , Dragan Massimo , Coulombe-Pontbriand Moise , Laird Colleen Simpson , Campbell Curtis
Published: December 2014

Linear infrastructure routing experts struggle with providing rationale for final route selections that are defensible, transparent, open to two-way stakeholder communication, and ultimately scientifically rigorous and repeatable. Likewise, proponents are wise to adopt a front-end, risk-based approach to proactively identify, mitigate or possibly avoid routing decisions that may result in stakeholder opposition and costly permitting and/or approval delays.

This paper discusses an approach using Geographic Information Systems (GIS) and a highly structured multi-criteria spatial analysis (MCA) to identify potentially optimal corridors and routes based on best available environmental, social, economic and technical spatial datasets. This approach can be used by multidisciplinary project teams to systematically capture, explore and record routing protocols and assumptions, and then extrapolate these considerations through GIS modelling into simulated corridor and route options which can then be quantitatively analyzed, compared, documented and communicated.

Early identification and mitigation of project routing risks may help reduce or avoid costly project delays at later stages. Stakeholder communication and consultation can be incorporated at each stage in order to inform routes and explore trade-offs, as well as communicate routing rationale in an open, constructive and meaningful way.

The resulting benefits of this approach include a robust and comprehensive rationale, providing proponents with a clear and compelling “story” in support of public and stakeholder consultation as well as the regulatory approval process.
A Practical Approach to Continuous Quality Control of Pipeline System Records
Authors: Lutz Andrew R. , Bubenik Thomas A.
Published: December 2014

In recent years there has been an industry wide initiative to verify operating pressures by reviewing source records and ensuring they are traceable, verifiable, and complete. A methodology was presented in a recent paper (A Practical Approach to Pipeline System Materials Verification by Lutz and Bubenik) to systematically review and organize records into an auditable framework (i.e. a GIS compatible listing or database). Once operators have completed their systematic records review, they are advised to maximize their investment by performing appropriate on-going records maintenance.

An effective records maintenance program will include the following elements to ensure effective management-of-change and continuous quality assurance and quality control. 1. Source documents will be made available to the company engineers and technicians that use the verified information to make everyday integrity and operational decisions (i.e. use a GIS interface to link verified information to the source documents). 2. A controlled process for management-of-change that effectively integrates new construction and replacement records into the existing database. 3. Continuously verify and cross-check pipeline system material properties with… a. …destructive material testing of any pipe that is removed or replaced. b. …in-the-ditch NDE methodologies, such as UT wall-thickness measurements and hardness to yield strength testing. c. …global survey data such as GIS and in-line inspection. 4. A controlled process to resolve records failures that includes the following steps: a. Identify and isolate the data point(s) that are the cause of the records failure. b. Establish a boundary around the potential extents of the records failure. c. Systematically investigate within the established boundary and verify the data discrepancies until the records failure is resolved to a reasonable certainty.

By implementing a records maintenance program with these elements, operators will ensure that their records database will be maintained and that the information being relied upon for daily integrity and operational decisions is reliable. Operators will decrease the likelihood of issues resulting from records failures and will ensure their records organization will with stand the scrutiny of future audits and records investigations.
Development of a 150°C Geopig Inertial Mapping Tool for Pipeline Strain Monitoring
Authors: Dreger Bruce , Waslen Doug , Barlow James , Smith James , Clark Melissa , Westwood Stephen
Published: December 2014

Pipeline strain monitoring using inertially-equipped pipeline inspection tools was developed in 1986 and is now an established method to identify pipe movement and associated bending strain. These pipeline inspections, however, are limited by the operating range of the electronics used in the inspection tools; these tools cannot be used for high-temperature pipelines that require strain monitoring. Suncor required that a high-temperature tool be designed and built for their 60 km Hot Bitumen (HotBit) pipeline from Firebag to Fort McMurray. Suncor approached various In-line Inspection providers to design an inertial mapping tool that would operate at temperatures to 150°C.

Suncor selected Baker Hughes Incorporated (BHI) for this development project based on their reputation and their historical development with respect to pipeline strain monitoring. This paper outlines the development process chosen for this project, the various technical challenges that were overcome, and presents the results from the In-line Inspections performed at three temperatures spanning 120 degrees.
The Reliability-Based Assessment of an In-Service X80 Natural Gas Pipeline in China
Authors: Wen Kai , Gong Jing , Zhao Boyuan , Zhang Wenwei , Zhang Zhenyong
Published: December 2014

Guidelines for the application of reliability-based design and assessment to natural gas pipelines were developed under PRCI sponsorship in 2005. The methodology underlying these guidelines has since been adopted as a non-mandatory Annex in the CSA Z662 standard (Annex O). Following the code in CSA Z662 Annex O, the reliability analysis of an in-service X80 pipeline in North-West China is performed using Monte Carlo technique. In this paper, the distributions of basic input parameters such as loadings, material property is derived based on the data collected from industrial practice. And the analysis of limit states, such as yielding of the defect-free pipeline, bursting of the defect-free pipeline, local buckling due to restrained thermal expansion and excessive plastic deformation, is proceeded based on these distributions. The core of reliability analysis lies in the selection and correction of limit state functions. The modification and extension of limit state models is very significant to accurately calculate probability of failure of different natural gas pipelines, so the limit state models are refined to adapt to the specific work conditions in China. A Monte Carlo reliability analysis framework capable of incorporating the data of industrial practice and limit state models has been developed and applied to the evaluation of the X80 natural gas pipeline, then a practical approximation is developed by using Monte Carlo simulation results. A practical example of an in-service X80 natural gas pipeline is presented to illustrate the availability of the reliability analysis. Furthermore, results generated by different basic input parameters in a limit state function are compared. The sensitivity analysis shows the degree of influence of various basic parameters.
Development and Validation of a Combined UM/UC In-Line Inspection Tool for a 36/48″ Pipeline System
Authors: Seto Laura , Hennig Thomas , Sickinger Thorsten
Published: December 2014

Within the global integrity program of Enbridge a 36/48″ dual diameter pipeline with a total length of approximately1800 km needs to be inspected for wall thickness and axial cracking in a single run. The line consists of 29 sections, each of an approximate length of 60 km. A challenging characteristic of the line is the 36″ launcher and 48″ receiver in 28 of the sections. Thus, the resulting outer diameter change is about 305mm or 33%. From an intelligent inspection perspective additional boundary conditions had to be taken into account, e.g. tight 1.5D bends and a medium with high attenuation — which is especially important for the crack inspection technology.

Pipeline operator and in-line inspection (ILI) vendor agreed on an extensive testing and qualification program including small scale tests (200 anomalies) and field verifications. Therefore, the operator witnessed pull tests of the 36/48″ UCM tool at the test facility in Stutensee, Germany during the development phase in 2012. The first inspection in an operating pipeline system, as part of the validation process, was made in July 2012 after only 12 months of development and construction. Some shortcomings of the tool concept were observed within the first inspection, which led to an unsuccessful run. Both parties worked closely together to implement some modifications to the tool. In 2012 and 2013 the modified tool was run a total of 29 times, with further runs planned for 2014.

The first excavations have been completed, and show an excellent correlation between tool performance and specification. Further excavations are scheduled for early 2014 that will provide additional feedback to assess and validate the tool. At the time of writing, the 36/48″ tool is fully validated for metal loss defects, and validated for cracks only up to 2.5mm in depth.

The authors will present in detail the development of the tool and the definition of the validation process. Mechanical and operational conditions are discussed. The predefined validation process of the tool is briefly presented and the test results are discussed in detail. Furthermore, field verification results are presented.
Applicability of Mandrel Elbow to High Pressure Gas Pipeline
Authors: Horikawa Hiroyuki , Toma Hideo , Yabe Yasuo , Tsukidate Mitsunori , Suzuki Nobuhisa
Published: December 2014

Applicability of mandrel elbows to high pressure gas pipelines is discussed in this paper taking into account the seismic integrity to withstand liquefaction-induced permanent ground deformation. Bending test and FE analysis of X65, 45 deg. mandrel elbow with diameter of 24-in were conducted in order to evaluate the seismic integrity for lateral spreading due to liquefaction.

Local buckling behaviors of the closing-mode test was simulated by FEA and calculation of existing seismic design code for high pressure pipelines can estimate maximum bending angle as limit state of the mandrel elbow conservatively. The results clarify that mandrel elbows can be applied to high pressure pipelines using conventional design method including the design code and FEA. In addition, buckling behaviors of the mandrel elbow were similar to those of high-frequency induction bends which have been used for high pressure pipelines in Japan.
Advanced Techniques for Establishing Long-Term Performance of Composite Repair Systems
Authors: Alexander Chris
Published: December 2014

Although composite materials are used to repair and reinforce a variety of anomalies in high pressure transmission gas and liquid pipelines, there continues to be widespread debate regarding what constitutes a long-term composite repair. The United States regulations require that composite repairs must be able to permanently restore the serviceability of the repaired pipeline, while in contrast the Canadian regulations take a more prescriptive approach by integrating the ASME PCC-2 and ISO 24817 composite repair standards along with a requirement for establishing a 50-year design life.

In this paper the author provides a framework for what should be considered in qualifying a composite repair system for long-term performance by focusing on the critical technical aspects associated with a sound composite repair. The presentation includes a discussion on establishing an appropriate composite design stress using the existing standards, using full-scale testing to ensure that stresses in the repair do not exceed the designated composite design stresses, and guidance for operators in how to properly integrate their pipeline operating conditions to establish a design life. By implementing the recommendations presented in this paper, operators will be equipped with a resource for objectively evaluating the composite repair systems used to repair their pipeline systems.
Identification Method of Oil Pipelines Technical Condition Based Upon Multigraph Models
Authors: Vladova A.
Published: December 2014

The problem of technical condition identification of aging oil pipelines in Russian Federation and in the world is relevant, since a significant number of them have been in service for over 30 years. More and more of them are getting closer to running out of normative resources. Within a method for reducing the size of task of identifying the technical condition of oil pipelines there were created special types of multigraph models (MGM) with interval-valued states of geometric characteristic of metallic shell defects.

Depending on oil pipelines operation time, the behavior of proposed models has been examined and operating performance with due account for technical condition identification has been determined, also the possibility of diminishing scope of inspections and repair works was shown. Multigraph models proposed here contain a set of states, which were singled out for the first time according to the analogue variable and are connected with multidirectional arcs with intensities of damage calculated on the relative amount of defects in the states.
Limit States Design for Onshore Pipelines: Methodology and Implications
Authors: Nessim Maher A. , Adianto Riski H. , Stephens Mark J.
Published: December 2014

A limit states design approach for onshore pipelines has been developed as part of a three-year joint industry project. The approach covers both natural gas and low vapor pressure (LVP) liquid pipelines and addresses key design conditions, including burst, equipment impact loads and plastic deformations during hydrostatic testing. The results are described in a set of design guidelines that can be used as a basis for a limit states design standard.

The design methodology is based on two limit states categories, namely ultimate limit states representing large leaks and ruptures, and serviceability limit states representing excessive deformations. For ultimate limit states, a safety class system is used to characterize pipelines based on the anticipated severity of failure consequences as determined by pressure, diameter, product, population density and environmental sensitivity. Simple deterministic design rules are then developed to ensure that appropriate reliability levels are met for each limit state category and each safety class.

Comparisons between the wall thicknesses resulting from limit states and conventional design methods are given for a wide range of pipeline diameters, pressures, grades and location classes (for gas pipelines). The results show that the limit states design approach results in thicker walls for small diameter pipelines (especially in highly populated or environmentally sensitive areas) and lower wall thicknesses for larger diameter, higher pressure pipelines (especially in areas with low population densities). The reason for this trend is explained and the potential for its acceptance by designers and regulators is discussed.
Ductile Fracture Behavior of Bainite-MA Dual Phase Steels
Authors: Shimamura Junji , Yasuda Kyono , Ishikawa Nobuyuki , Endo Shigeru
Published: December 2014

In order to achieve safety and reliability of the pipeline installed in seismic region, it is quite important to apply the high-strength linepipes with sufficient strain capacity against buckling and weld fracture by the seismic ground movement. Dual-phase microstructure control is an essential measure for improving strain capacity of linepipe steels. Ferrite-bainite or bainite-MA microstructures are practically applied to the linepipes for the strain-based design to achieve higher deformability which has low Y/T (Yield/Tensile strength) ratio and high uniform elongation even after pipe coating. On the other hand, dual-phase steels tend to show lower Charpy energy in the upper shelf region than single-phase steel. It is considered that void nucleation and growth is enhanced in the dual-phase steels due to the strain concentration at the boundary between two different phases, resulting in early cracking in the specimen that leads to lower Charpy energy.

The Charpy energy of the bainite-MA dual-phase steels was strongly affected by the volume fraction and size of MA. In the case of Bainite-MA steels with fewer volume fraction of MA and smaller size of MA, the sample showed higher Charpy energy. Ductile fracture behavior was investigated through several kinds of Charpy impact tests in order to clarify the effect of these microstructure differences on the Charpy energy in the upper shelf region. From the SEM observation, it was found that void nucleation was enhanced in the sample with higher volume fraction of MA and larger size of MA. It is considered that the increase of boundary area that works as void nucleation site affected these results. Experimental results were mainly discussed in this paper.
A Case Study in High Strain Capacity Pipeline Qualification: PNG LNG Project
Authors: Noecker Fredrick F. , Fairchild Doug , Cook Mike , Macia Mario , Kan Wan
Published: December 2014

The onshore pipeline portion of the Papua New Guinea Liquefied Natural Gas (PNG LNG) project traverses terrain with seismically active faults with potential ground displacements up to four meters. The resulting longitudinal strain demand exceeds 0.5% strain, thereby requiring use of strain-based pipeline design (SBD) technology. This paper discusses the application of previously developed strain-based design methodologies to successfully qualify the PNG LNG pipeline system for a design tensile strain demand up to 3%, and flexibility to increase the design strain demand with additional restrictions on key variables impacting strain capacity at select locations. Key SBD pipeline qualification activities are discussed along with the required project timeline. The first activity is specifying, evaluating and procuring line pipe suitable for strain-based design. SBD line pipe must be strain-age resistant, have excellent longitudinal uniform elongation, and have tightly controlled ultimate tensile strength (UTS) limits to ensure robust girth weld overmatch. The girth welds must exhibit upper shelf fracture toughness, excellent tearing resistance, and have sufficient tensile strength to ensure adequate girth weld strength overmatch. The pipeline qualification effort culminates in full scale pipe strain testing as proof of performance. The specimens for these tests are fabricated with project-specific pipe, girth welds, and pipe fit-up (hi-lo misalignment). The girth welds contain machined flaws in both weld metals and heat affected zones, these flaws being sized consistent with acceptable flaw sizes predicted from analytical models and prior experience. The results of these tests and their significance are described. Efforts to reduce capacity through lowering strain demand are outlined, along with examples of construction challenges the project has successfully faced. Key engineering and project decisions, and lessons learned from this qualification effort are also detailed.
Evaluation of Existing Fracture Mechanics Models for Burst Pressure Predictions, Theoretical and Experimental Aspects
Authors: Tandon Samarth , Gao Ming , Krishnamurthy Ravi , Kariyawasam Shahani , Kania Richard
Published: December 2014

The predictions of burst pressure and leak/rupture have significant impact on the pipeline integrity assessment results, and subsequently on the extent of the required mitigation and re-inspection interval. There are models available for burst pressure and leak/rupture prediction in the literature, namely API-579, CorLas®, and NG-18 (Modified Ln-Sec). In this paper, evaluation of existing fracture mechanics models for burst pressure and leak/rupture prediction for external crack and crack like features including stress corrosion cracks (SCC) are performed. Both theoretical and practical aspects of each model are discussed in detail. An experiment is set up to conduct fifteen full scale burst tests of 20-inch, 34-inch and 36-inch diameter joints removed from the pipeline field. Among them, seven pipe joints are with base material SCC, four joints with seam weld cracks, three joints with linearly aligned crack-like features surrounded with shallow base material SCC, and one joint with crack-like feature in the Weld area. A high speed camera is utilized to capture rupture events. The rupture events can be stable tearing, crack coalescence and unstable propagation of a critical crack or multiple closely aligned cracks in a crack colony which are responsible for the rupture. Detailed profile measurements of the critical crack/s for burst pressure predictions are done from the fracture surfaces. Relevant material properties are measured for each joint in base material or seam weld location depending on the crack location. Burst pressure predictions are performed with models available in API-579, CorLas®, and Modified NG-18. An elastic-plastic finite element model is generated to quantify the effective stress intensity factor with and without the end cap effects during the burst testing. The accuracy and conservatism of the models evaluated are analyzed. Implications of the findings are discussed.
Numerical Simulation of Stratified Two-Phase Flow in a Nearly Horizontal Gas-Liquid Pipeline With a Leak
Authors: Bueno David E. G. P. , Figueiredo Aline B. , Baptista Renan M. , Rachid Felipe B. F. , Bodstein Gustavo C. R.
Published: December 2014

The capability of producing accurate numerical simulations of transient gas-liquid flows in gas pipelines has long been a serious concern in the oil industry. In this paper we are particularly interested in simulating this type of flow during the occurrence of a leak in the pipe. We use the flux-corrected transport (FCT) finite-difference method, which is second-order in space, to solve a one-dimensional single-pressure four-equation two-fluid model. We consider this two-phase flow to occur in a nearly horizontal pipeline characterized by the stratified-flow pattern, and we assume that the flow is isothermal with a compressible gas phase and an incompressible liquid phase. We model the leak as a source term in the mass conservation equations. The results of the numerical simulations allow the model sensitivity to be studied by changing the leak diameter and the leak location. From this analysis, we may observe how these parameters affect the pressure gradients along the pipeline that develop upstream and downstream of the leak.
Allowable Pressure Cycling Limits for Liquid Pipelines
Authors: Sutton Aaron , Hubert Yvan , Textor Steven , Haider Syed
Published: December 2014

While pressure fluctuation is an inherent part of operating pipelines, review of historic operations of several pipelines in the years leading up to a failure shows a trend in the severity level of the pressure cycling. It was recognized that moderate to severe levels of pressure cycling are not acceptable on a pipeline for an extended period of time. As a result, pipelines that are operating at, or worse than this severity level have a higher likelihood of failure due to the potential fatigue crack growth induced by the pressure fluctuations.

Enbridge has developed a managed approach to addressing the ramification linked to reducing pressure cycling on its system to address both existing and new assets. This approach is presented in paper IPC2014-33485 “Pressure Cycle Management”. This paper discusses the particulars for establishing targets to help with driving and monitoring the success of pressure cycling mitigation activities.

Each pipeline is given different pressure cycling targets using a risk based approach taking into account the current condition and pipe properties of the pipeline, i.e. cracking susceptibility. Factors like feature population and distribution, vintage of pipe, longseam weld type, failure history, ILI technology used to inspect the pipeline, and when the last hydrostatic test took place are taken into account when determining the pressure cycling targets. The more susceptible to in-service crack growth that a pipeline represents, the more stringent the pressure cycling targets will be.

Pressure cycling severity is determined with a methodology based on TTO Number 5 and fatigue modeling. The challenge is in converting the pressure cycling severity target into meaningful cycling targets that can be used to reduce the cycling. The severity target is transformed into typical maneuvers performed on the pipeline to give operators and schedulers an idea of how many cycles and of what magnitude they have to work with to still meet the cycling severity target.