bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Damage Mechanics Modeling to Strain Based Design With Respect to Ductile Crack Initiation
Authors: Ishikawa Nobuyuki , Sueyoshi Hitoshi , Igi Satoshi
Published: April 2011

Limit state condition in the tensile failure for the strain based-design (SBD) currently considering is the point of maximum load which is evaluated by curved wide plate (CWP) testing or full scale pipe tensile testing. Maximum loading point is understood as the onset of instability of the structure. However, the material behavior controlling structural instability is not well understood since it includes many aspects of material response such as local strain concentration, ductile crack initiation and stable crack growth. In order to clearly specify the material property suitable for SBD, it is important to understand the fundamental behavior of the linepipe steels that leads to ductile crack initiation and following ductile tearing. In this paper, critical condition for ductile crack initiation was investigated by both small scale and large scale testing, notched round bar and wide plate testing, by using X80 and X100 linepipe steels and welds. Two different analytical procedures, equivalent plastic strain criterion and damage mechanical analysis, were applied to evaluate the local material conditions for ductile crack initiation. As was already verified by many other researches, the critical equivalent plastic strain can be used as the local criterion for ductile crack initiation which is not affected by specimen geometry. However, equivalent plastic strain is still macroscopic parameter that is not reflected by microscopic feature of the steel. Therefore, the Gurson-Tvergaard damage mechanical model was applied to further understand microscopic material behavior to ductile crack initiation. Material parameters for G-T model were carefully evaluated depending on the microscopic characteristics of each steel. By selecting appropriate material parameters, the critical condition for ductile crack initiation was estimated by the critical void volume fraction, which is independent of specimen geometry. Effect of microstructural characteristics on crack initiation was also investigated in this study.
The Follow-Up of an Extensive Portfolio
Authors: Modica Jose Eduardo , Martins Marcelo Ramos , Rabechini Roque , Martins Braun Edison
Published: April 2011

The speed of the changes that have occurred in the world have forced organizations to adapt themselves and offer new products to the consumers in increasingly shorter timeframes, or risk being overtaken by the competition. The cycle of project life is being reduced, making the management increasingly complex both for the projects and portfolios of projects. Included in this scenario are companies from the oil sector that act to develop management systems that manage to aggregate greater chances of success for its projects as well as the capacity to manage multiple projects simultaneously. The concept of success itself is controversial, because on the one hand it is one of the most researched topics, on the other there is still no consensus among those interested. It becomes necessary then to understand the concept of success for projects, and to establish ways of measuring it, and try to identify the critical factors of success and the critical factors of failure, so that organizations can manage their own projects adequately. Companies with extensive project portfolios confront greater challenges, because they have to develop efficient methodologies to manage and maintain their portfolios, in addition to having to develop competences to accompany the management of multiple projects, identifying possible corrective actions for the deviations identified in time. One efficient manner of pro-actively controlling extensive portfolios of projects being executed simultaneously at different geographical locations is the utilization of a tool via web that integrates all the management activities. This tool must have as a basic premise its utility for the work of the management team, and not only be a communication tool, since in this case it would call for an effort by the management team that adds no value to the project. This article has the objective of showing the results of research carried out to identify how Transpetro, the largest logistics company in South America, which operates a fleet of 55 ships with transport capacity of 2.9 million deadweight tons, 7,033 km of oil pipelines and 3,600 km of gas pipelines, 20 land-based terminals and 26 water-based terminals, controls its engineering projects, directing its efforts in an attempt to achieve greater chances of success so as to comply with its strategic planning.
Three-Dimensional Response of Buried Pipelines Subjected to Large Soil Deformation Effects: Part II—Effects of the Soil Restraint on the Response of Pipe/Soil Systems
Authors: Fredj Abdelfettah , Dinovitzer Aaron
Published: April 2011

Understanding the effect of soil-pipeline interactions in the event of large ground movement is an important consideration for pipeline designer. Both experimental investigation and computational analyses play significant roles in this research. As part of this effort, a framework incorporating continuum soil mechanics and advanced finite element approach (i.e., ALE and SPH method) for modeling soil pipe interaction is developed. The overall objective is to develop, validate and apply 3D continuum modeling technique to assess the performance of pipeline system subjected to large soil displacement. The numerical models than may be used to predict the wrinkle formation and post formation behavior of the pipeline considering the effect of the soil confinement, and develop a comprehensive wrinkle integrity assessment process. This is the second paper (Part II) in a series of two papers. In the first paper a three-dimensional Continuum models using MM-ALE (Multi-material Arbitrary Eulerian Lagrangian) and SPH (smooth particle hydrodynamics) approaches are developed and run using LS-DYNA. The results are compared with published experimental data of large-scale test to verify the numerical analysis methods. In this paper (Part II) the effects of soil restraint on the response of the pipe/soil systems (e.g., pipeline Wrinkle and buckle, strain demand) are discussed.
Implications and Trends in SMYS Built Into Pipelines
Authors: Leis Brian N. , Clark E. B. Ted
Published: April 2011

For many the use of SMYS in conjunction with working-strength design for pipelines leads to the expectation that the least strength of the joints in the pipeline is at or above SMYS. In contrast, regulations relevant to pipeline operation reference specifications require limited testing to demonstrate the acceptance of pipe joints made from a “heat” of steel, and where such testing fails such specifications admit a retest. Thus, contrary to the expectation of that all joints constructed into a pipeline achieve SMYS, the statistical reality is that some joints can have strengths that fall below this design expectation. This paper considers the implications of changes due to the globalization of the steel and pipe-making industries relative to the historical evolution of classes/grades of steel and their processing in regard to the statistical properties of line pipe built into a pipeline. It is shown for the data evaluated that, in spite of globalization and other aspects that tend to diminish quality such as increasing heat-volume, controls affected in steel and pipe production can lead to better quality today as compared to historical scenarios. Circumstances that can compromise this outcome are identified and discussed.
Repair of Dents Subjected to Cyclic Pressure Service Using Composite Materials
Authors: Alexander Chris , Bedoya Julian
Published: April 2011

For the better part of the past 15 years composite materials have been used to repair corrosion in high pressure gas and liquid transmission pipelines. This method of repair is widely accepted throughout the pipeline industry because of the extensive evaluation efforts performed by composite repair manufacturers, operators, and research organizations. Pipeline damage comes in different forms, one of which involves dents that include plain dents, dents in girth welds and dents in seam welds. An extensive study has been performed over the past several years involving multiple composite manufacturers who installed their repair systems on the above mentioned dent types. The primary focus of the current study was to evaluate the level of reinforcement provided by composite materials in repairing dented pipelines. The test samples were pressure cycled to failure to determine the level of life extension provided by the composite materials relative to a set of unrepaired test samples. Several of the repaired dents in the study did not fail even after 250,000 pressure cycles were applied at a range of 72% SMYS. The results of this study clearly demonstrate the significant potential that composite repair systems have, when properly designed and installed, to restore the integrity of damaged pipelines to ensure long-term service.
Girth Weld Failure in a Large Diameter Gas Transmission Pipeline
Authors: Scrivner Ron , Exley Butch , Alexander Chris
Published: April 2011

There have been several recent weld failures either during the initial post construction hydrostatic tests, or immediately following construction. Girth welds typically do not fail as a result of internal hoop loads without the contribution of loads due to out side forces. External loading should be considered during design, welding procedure development, construction, and pipeline operations. This paper presents one example where a girth weld failed as a result of preexisting 1940’s weld imperfections and recent, 1980’s, external loading. This analysis of the girth weld failure in the 30-inch pipeline included an initial failure analysis, a fracture mechanics analysis, and a finite element analysis that integrated the pipe-soil interaction, as well as localized stresses associated with weld imperfections. A critical part of this study was to evaluate how changes in soil conditions associated with a drought followed by soil saturation associated with rainfall, contributed to lack of local support and increased overburden loads associated with the saturated soil. The failure analysis of the ruptured girth weld and surrounding pipe concluded that the failure of the girth weld was caused by increased bending loads imposed on the pipeline after recent construction activities, and that the fracture initiated at a lack-of-penetration/fusion imperfection that was 20 1/4-inches long and 0.110 inches deep. A coupled investigation using finite element and fracture mechanics analyses verified numerically that with reduced-strength soil, stresses were generated in the girth weld of sufficient magnitude to cause a fracture. Temperature, terrain, and fatigue were considered, but were not deemed to significant enough to affect the stresses or other conditions that resulted in the failure. The overriding observation of this study is that no single factor contributed to the failure that occurred. Rather, the girth weld failure was the result of weld imperfections that generated elevated stresses due to excessive loads imparted to the pipe due to settlement associated with non-compact backfill associated with excavation work. Had the pipe not displaced vertically due to localized soil conditions, it is unlikely that the pipeline would have failed. The recent excavation activities were adequate for normal soil conditions; however, dry soil at the time of construction resulted in lack of compaction and excessive moisture just prior to the failure that generated in differential settlement and heavy overburden, combined with lack of penetration imperfection in the girth weld in question, resulted in generating excessive bending stresses that contributed to the eventual failure of the pipeline.
Limit State Design Based on Experimental Methods for High Pressure Subsea Pipeline Design
Authors: Alexander Chris
Published: April 2011

The design of offshore subsea pipelines is facing new challenges as the pipeline industry is moving into environments requiring high pressure design. Conventional pipeline design codes such as ASME B31.4 and B31.8 establish pressure limits based on percentage of the pipe material’s minimum specified yield strength. While this has traditionally worked for relatively thin-walled pipe at moderate pressures, there are concerns that full utilization of the material’s capacity is not being realized when designing for high pressure conditions. Additionally, there are concerns regarding the ability to achieve high quality manufacturing and consistently fabricate welds in thick-wall pipes. This paper presents details on a testing program that incorporated full-scale burst testing to qualify the design pressure for an 18-inch × 0.75-inch, Grade X65 subsea gas pipeline using the methodology of API RP 1111. A lower bound burst pressure was established based on the recorded burst pressures to which a design margin of 0.72 was applied to determine a design pressure. Had the pipeline been conventionally-designed using ASME B31.8, the design pressure would have been 3,900 psi. However, using the experimentally-based design option in API RP 1111 the resulting design pressure was 4,448 psi. This results in a net increase in the design pressure of 14 percent. When one considers either the potential cost savings in material requirements at construction or the additional throughput associated with higher design pressures for a given pipeline system, it is not difficult to demonstrate the economic benefits derived in performing a more rigorous material qualification and limit state design process based on experimental methods as presented in API RP 1111.
Development of Industry Standards for Composite Repair Systems
Authors: Alexander Chris , Worth Franz
Published: April 2011

A significant amount of work has transpired over the past several years in generating consensus-based standards that include ASME PCC-2 and ISO 24817 for developing composite repair systems. The intent in developing these standards has been to provide industry with guidelines for designing composite repair systems to ensure that damaged pipelines and piping systems are safely and properly reinforced. With the numerous composite repair systems currently available to pipeline operators, the importance of evaluating the capabilities of each system cannot be overstated. The fundamental design variables available to manufacturers are stiffness, strength, and thickness of the composite. A properly-designed repair system ensures that strains in the reinforced steel and reinforcing composite material do not reach unacceptable levels. This paper provides a basic overview of the design philosophy embedded into the current design codes, as well as presenting results associated with several specific studies that were conducted to evaluate composite repair performance.
Predictions of Cleavage Fracture in Welded Components Incorporating Strength Mismatch Effects: A Weibull Stress Based Approach
Authors: Ruggieri Claudio
Published: April 2011

This work describes the development of a toughness scaling methodology incorporating the effects of weld strength mismatch on crack-tip driving forces. The approach adopts a nondimensional Weibull stress, σ¯w, as a the near-tip driving force to correlate cleavage fracture across cracked weld configurations with different mismatch conditions even though the loading parameter (measured by the J-integral) may vary widely due to mismatch and constraint variations. Application of the procedure to predict the failure strain for an overmatch girth weld made of an API X80 pipeline steel demonstrates the effectiveness of the micromechanics approach. Overall, the results lend strong support to use a Weibull stress based procedure in defect assessments of structural welds.
The Effect of Hot Strip Mill Processing Parameters and Alloy Addition on Low Temperature Toughness of API-X70 Steel
Authors: Ro Kwang Seop , Al-Shammary Saad , Al-Butairi Adel A. , Al-Hajeri Khaled F.
Published: April 2011

Correlation of rolling conditions, microstructure, and low-temperature toughness of X70 pipeline steels was investigated in this study through statistical analysis. High strength API X70 steel grade with excellent DWTT toughness can be designed by the developed statistical equation. The predicted equation is as follows; ‘Pct Shear area of DWTT (−10°C) = 954 − 0.3*SRT + 0.5*TBT − 0.4*FRT + 0.04*CT − 306*C −60*(Mn+Ni+Cu) + 38*(Mo+Cr) − 791*(Ti+Nb+V) − 4*MA’ and the predicted equation showed very good relationship. M/A constituent showed high relationship with DWTT toughness. By inserting this effect into the equation, the reliability of the equation has been improved. By using the prediction equation, new chemical composition and relevant processing variables could be optimized and newly designed steel shows proper tensile properties with the excellent DWTT toughness at −10°C.
Repair of High Pressure Pipe Fittings Using Composite Materials
Authors: Bedoya Julian , Alexander Chris , Precht Tommy
Published: April 2011

Pipelines and piping frequently suffer from metal loss that threatens their integrity and serviceability. Multiple repair options exist for straight sections of pipe; however, repair options for pipe fittings such as elbows and tees are typically limited to composite repair systems, or section replacement. The latter method can be costly as it often requires at least a partial shut down of the pipeline while the section is replaced. A composite repair system however, can be performed in place during operations at a greatly reduced cost. The main challenge with the composite repair system is the required demonstrated ability to restore integrity and serviceability to the same level as the original metal system. Over the past 10 years, Stress Engineering Services, Inc. has been greatly involved in evaluating the ability of many composite repair systems to restore the original pipeline structural integrity by testing methods and analysis methods. The current paper investigated the ability of the Armor Plate Pipe Wrap (APPW) system to restore the burst pressure of tee and elbow pipe fittings with 60% metal loss to that of a nominal thickness system. In this program four full scale burst tests were conducted: on 12-inch nominal pipe size (NPS) Y52 tee and elbow pipe fittings. All four fittings had 60% metal loss; two were repaired with APPW, and the other two were not repaired. Prior to burst testing, elastic plastic finite element analyses (FEA) were performed to adequately size the repair thickness. The results of the FEA calculations predicted the restoration of the burst pressures of the repaired fittings up to a 1.6% agreement with the actual burst pressure results. Furthermore, the burst pressure of the 60% metal loss tee was increased from 3,059 psi (unrepaired) to 4,617 psi, or a 51% improvement. The burst pressure of the 60% metal loss elbow was increased from 2,610 psi to 4,625 psi, or a 77% improvement. Both the analysis and testing results demonstrated that composite materials can restore the pressure integrity of corroded tee and elbow pipe fittings.
A Systematic Approach for Evaluating Dent Severity in a Liquid Transmission Pipeline System
Authors: Alexander Chris , Jorritsma Eelco
Published: April 2011

An API 579 Level 3 assessment was performed to determine the stresses in a 2% dent in a 20-inch × 0.406-inch pipeline. The intent was to determine the stress concentration factor (SCF) in the dent with a finite element model using geometry data provided from an in-line inspection caliper run. In addition to the analytically-derived SCF, data were also evaluated from a recent experimental study involving a plain dent subjected to cyclic pressure conditions with a profile comparable to the dent in question. This sample was cycled at a stress range of 70% SMYS and failed after 10,163 cycles had been applied. Using the DOE-B mean fatigue curve, combined with the experimental fatigue life, the resulting SCF factor was derived to be 4.20. This value is within 1% of the calculated FEA-based SCF and served to confirm the technical validity of the SCF. The operator provided historical pressure data covering a 12-month period and a rainflow count analysis was performed on the data. Using this data, along with the API X′ design fatigue curve, the estimated remaining life was determined for the dent in question and conservatively estimated to be 65 years. This paper provides details on the analysis methodology and associated results, discussions on the empirically-derived SCF with its use in validating the analytical SCF, and application of the results to estimate the remaining life of the pipeline system. It is the intent of the authors to provide the pipeline industry with a systemic approach for evaluating dent severity using caliper and operating pressure history data.
Brazilian Gas Network Computational Model for Reliability Analysis
Authors: Carvalho Thomaz , Bilhim Thiago , Ferreira Gustavo P. D. , Pires Luis F. G. , Faertes Denise , Saker Leonardo
Published: April 2011

This paper presents a discussion of the alternatives and strategies used in the thermo-hydraulic simulation of the Brazilian gas pipeline network. It analyses the advantages and disadvantages of each approach and the option used in order to meet the demands of the overall reliability analysis developed by the Gas Reliability Management Sector of PETROBRAS.
Data Analysis in Parallel With GIS Systems
Authors: Polasik Steven J. , LeMesurier Michelle , Alfano Tony , Delanty Burke , Bubenik Thomas
Published: April 2011

The processing and integration of data for direct assessment (DA) and in-line inspection (ILI) comparisons is critical to making sound integrity-based decisions. While geographic information systems (GIS) are now commonly used to model pipeline systems, most day-to-day data processing and integration occurs outside of the GIS, for example in Microsoft Excel™. As such, Det Norske Veritas (DNV) developed a data integration tool within Excel™ as part of a large scale stress corrosion cracking direct assessment (SCCDA) program for a major pipeline operator. Linear based data provided by the client (e.g., in-line inspections, girth welds, previous excavations, close interval survey, coating, grade and wall thickness, pressure history, road and water crossings, risk assessments, landowner information, etc.) is processed, analyzed and incorporated into the overlay. This tool provides the ability to integrate any linear based data in a graphical representation of the pipeline along continuous and parallel chainage. The overlay allows for identifying similar locations using criteria that are difficult to program into an algorithm and helps engineers to relate complex factors during the decision making process. The overlay also provides the ability to easily extract data relevant to sites selected for assessment along the pipeline. The data integration tool has already found many applications beyond SCCDA since it provides a robust process to integrate and analyze data in parallel with GIS systems. The overlay provides engineers with a method to make decisions without learning complex GIS programs and has the added ability to feed the results back into GIS systems. Such decision making processes and applications include direct assessment programs, cathodic protection enhancements, risk reduction programs, in-line inspection comparisons, and maintenance activities.
Transient Simulation of Natural Gas Citygates Stations
Authors: Barreto Claudio Veloso , Pires Luis F. G. , Sarmento Renata C.
Published: April 2011

The demand of natural gas in the Brazilian energy market is increasing very fast over the few years and it was necessary to enhance the operational performance and safety of the gas distribution. The perfect operation of the natural gas citygate stations is essential to guarantee the delivery of natural gas for the end users like local distribution companies, thermoelectric power plants and large industrial customers within the contracted marketing conditions. These stations receive natural gas directly from high pressure pipelines and reduce the pressure using regulation valves that provoke a temperature reduction due the Joule-Thompson (JT) behavior, typical of natural gases. This temperature loss is compensated by forcing part of the gas flow through water/glycol bath heaters that use natural gas as fuel in the heating process. Usually the downstream gas temperature condition is controlled above a minimal set point while modifying the three-way valve position that regulates hot and cold streams flows. A numerical tool has been developed to simulate the dynamic process inside the natural gas citygate station, and proved to be a reliable tool to analyze the transient performance of the main equipments (filter, three way valve, heater, JT valve, relief valves) when submitted to abnormal conditions or changes in capacity. The methodology developed is able to handle a variety of citygate design.
GASDECOM: Carbon Dioxide and Other Components
Authors: Cosham Andrew , Eiber Robert J. , Clark Edward B.
Published: April 2011

Carbon dioxide (CO2) pipelines are more susceptible to long running fractures than hydrocarbon gas pipelines because of the decompression characteristics of CO2. The key to understanding this issue is the phase diagram and the liquid-vapour phase boundary. GASDECOM — based on the BWRS equation of state — is a program widely used for calculating the decompression behaviour of mixtures of hydrocarbons. The calculated decompression wave velocity curve is then used in models such as the Battelle Two Curve Model to determine the toughness required to arrest a propagating ductile fracture. GASDECOM is capable of modelling mixtures of hydrocarbons (methane through to hexane), nitrogen and carbon dioxide. It therefore can (and has) been used to investigate the effect of methane and nitrogen on the decompression characteristics of CO2. Pipelines can be expected to play a significant role in the transportation infrastructure required for the successful implementation of carbon capture and storage (CCS). The composition of the carbon dioxide rich stream to be transported in a pipeline depends on the capture technology, e.g. post-combustion, pre-combustion and oxy-fuel. Post-combustion tends to result in an almost pure stream. The other capture technologies produce a less pure stream, containing potentially significant proportions of other components such as hydrogen, nitrogen, oxygen, argon and methane. One of the factors that will constrain the design and operation of a carbon dioxide pipeline is the effect of these other components on the decompression characteristics, and hence the arrest toughness (amongst other issues). Components such as hydrogen, oxygen and argon cannot currently be considered using GASDECOM. Through a study of the underlying algorithms implemented in GASDECOM, it is shown how GASDECOM can be modified to include these additional components relevant to carbon capture and storage. The effect of impurities such as hydrogen on the decompression characteristics is then illustrated, and related back to their effect on the phase diagram and the liquid-vapour phase boundary. The sensitivity of the results to the use of equations of state other than BWRS is also illustrated. Simplifications that follow from the decompression behaviour of carbon dioxide are also highlighted. Finally, the small and large scale experimental studies that are required to validate predictions of the decompression behaviour and the arrest toughness are discussed.
Estimation of Corrosion Rates by Run Comparison: A Stochastic Scoring Methodology
Authors: Nicoletti E´rika S. M. , de Souza Ricardo D.
Published: April 2011

Pipeline operators used to map and quantify corrosion damage along their aging pipeline systems by carrying out periodical in-line metal-loss inspections. Comparison with the data sets from subsequent runs of such inspections is one of the most reliable techniques to infer representative corrosion growth rates throughout the pipeline length, within the period between two inspections. Presently there are two distinct approaches to infer corrosion rates based on multiple in-line inspections: individual comparison of the detected defective areas (quantified by more than one inspection), and comparison between populations. The former usually requires a laborious matching process between the run-data sets, while the drawback of the latter is that it often fails to notice hot-spot areas. The object of this work is to present a new methodology which allows quick data comparison of two runs, while still maintaining local distinct characteristics of the corrosion process severity. There are three procedures that must be performed. Firstly, ILI metal-loss data set should be submitted to a filtering/adjustment process, taking into consideration the reporting threshold consistency; the possible existence of systematic bias and corrosion mechanisms similarity. Secondly, the average metal-loss growth rate between inspections should be determined based on the filtered populations. Thirdly, the defects reported by the latest inspection should have their corrosion growth rates individually determined as a function of the mean depth values of the whole population and in the defect neighborhood. The methodology allows quick and realistic damage-progression estimates, endeavoring to achieve more cost-effective and reliable strategies for the integrity management of aged corroded systems. Model robustness and general feasibility is demonstrated in a real case study.
Full Scale Cyclic Fatigue Testing of Dented Pipelines and Development of a Validated Dented Pipe Finite Element Model
Authors: Bolton Brock , Semiga Vlado , Tiku Sanjay , Dinovitzer Aaron , Zhou Joe
Published: April 2011

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 goal of the full scale experimental program described in this paper is to compile a database of full scale dent test results that encompasses many of the dent types seen in the field, including plain dents, dents interacting with girth and long seam welds, and dents interacting with metal loss features, in both the unrestrained and restrained condition. The dents are pressure cycled until a fatigue failure occurs in the dent. Typical data recorded includes indentation load/displacement curves, applied pressures, pipe wall OD strains along the axial and circumferential centerlines, and axial and circumferential dent profiles. The full scale tests are being performed on behalf of PRCI and US DoT. This paper is intended to show the matrix of dents considered to date and present a representative summary of the data recorded. In addition to presenting the full scale test program and resulting data, this paper summarizes ongoing efforts to develop a validated pipeline dent integrity assessment model. The model under development makes use of the aforementioned full scale experimental data, to validate a finite element model of the denting and re-rounding process for a variety of dent scenarios (i.e. depths, restraints, indenter sizes). The paper discusses the efforts under way to develop and validate the finite element model with the goal being to estimate the fatigue life. The paper is an extension of work discussed in a previously presented IPC paper [1].
Prediction and Comparison of Burst Pressure for Line Pipes
Authors: Zhu Xian-Kui , Leis Brian N.
Published: April 2011

Accurate prediction of burst pressure in line pipes is critical for their safety design and operation. Different equations for predicting burst pressure of line pipes have been proposed over the years, but broad agreements between the prediction equations did not exist. To this end, the present authors recently developed a new multi-axial plastic yield theory that is referred to as Average Shear Stress Yield (ASSY) theory [6]. Based on this theory, a theoretical closed-form solution for predicting burst pressure was proposed as a function of the pipe diameter, thickness, ultimate tensile stress and strain hardening exponent. The results showed that the ASSY-based burst pressure solution predicts generally the average of experimental data, and gives the best prediction among different models in a comparison of over 100 full-size burst tests for different line pipe geometries and grades. This conclusion is consistent with the observation by Zimmerman et al. [7]. On the other hand, Law at al. [1–3] recently proposed a so-called CIS (cylindrical instability stress) model that can implicitly predict the burst pressure of line pipes, and claimed that the CIS model is the best one for predicting burst pressure. To clarify the argument and to determine a truly accurate prediction equation, this paper will reevaluate the available models of burst pressure using various experimental data used by Law et al. and others. Detailed comparisons and discussions on the predictions of burst pressure with the experimental results are performed.
Effect of Axial Tensile Strain on Yield Load-Carrying Capacity of Pipelines
Authors: Zhu Xian-Kui , Leis Brian N.
Published: April 2011

This paper theoretically investigates the effect of axial tensile strain on the plastic yield load-carrying capacity of pipelines. The elasticity theory and three plastic yield criteria of Tresca criterion, von Mises criterion, and Average Shear Stress Yield (ASSY) criterion are adopted in the analysis. General solutions of elastic stresses and strains are obtained for a thin-walled, end-caped pipe subjected to internal pressure and an axial strain that is used to represent the outside applied force. Based on the three plastic yield criteria, different nonlinear governing equations are obtained for determining the yield pressure, the yield hoop and axial stresses as well as the yield hoop and radial strains for the pipe. The results showed that the pressure, stresses and strains in the pipe at yield are functions of the axial strain, Poisson’s ratio, Young’s modulus, and yield strength of the pipe steel. The tensile strain limits are then obtained for different pipeline grades. It is concluded that the axial tensile strain can significantly reduce the limit load or the regulation-allowed operating pressure, and the tensile strain limits should be considered in strain-based design to prevent pipeline failure.
An Assessment for Structural Reliability of Offshore Risers due to Probability of Fatigue Failure
Authors: Morooka Celso K. , Stefane Wania , Matt Cyntia G. C. , Franciss Ricardo , Basilio Leandro
Published: April 2011

Different configurations for riser systems have been emerged as suitable technological and economical solutions for offshore petroleum fields in ultra deep water. The study and development of methodologies for riser project considering the uncertainties involved in the manufacture process of offshore risers and effects of meteocean conditions, such as waves, current and platform motions for the fatigue failure is fundamental to increase the reliability of riser structure design. The present work presents a procedure to evaluate the probability of fatigue failure in offshore Steel Catenary Risers (SCR) identifying the influence of the main parameters in the failure process due to fatigue. Meteocean conditions and uncertainties due to accumulated fatigue damage given by Miner-Palmgren’s rule are here considered. The probabilistic methodology is taken into account, and the analytical approach based on the First Order Reliability Method (FORM) is applied considering two practical cases. In the first case, calculations are performed to compare with the results from the literature, and the second one calculation is carried out considering a typical Brazilian offshore field operation. In the calculations, results for the probability of failure, as well as, the riser service life are observed in four different locations along the SCR length. Finally, conclusions are shown to the probability of failure due to fatigue such as influence of each parameter in the process.
UKOPA Dent Assessment Algorithms: A Strategy for Prioritising Pipeline Dents
Authors: Race Julia M. , Haswell Jane V. , Owen Robert , Dalus Barry
Published: April 2011

As in-line inspection tools improve, dents that would have been below the detection and reporting levels of previous inspections are now being detected and reported to pipeline operators. Consequently, operators are being faced with large numbers of dents in ILI reports that require further consideration and are left with the problem of how to prioritize these dents for further investigation and repair. Although code guidance is clear on the relative severity of dents associated with other features or those based on a depth or strain criteria, this may still leave a significant number of dents in the pipeline which fall within codified static dent assessment criteria, but which may still pose a threat, particularly from fatigue. Many transmission pipelines in the UK are now 30–40 years old and fatigue failures at dent locations are starting to be reported. Such occurrences have raised technical concerns with regulators regarding the perceived conservatism of current dent assessment methods as the dents in question were within the code limits and were reported through standard ILI technologies, however, they were not identified as significant. There is therefore a requirement to develop best practice guidance for the safe and economic operation of dented pipelines. The UK Onshore Pipeline Association (UKOPA) recognized that further guidance was needed in order that operators could identify dents which can be safely left in the pipeline and those for which further excavation is required. They have consequently developed a series of algorithms to allow pipeline operators to prioritize the dents for repair based on ILI results. This paper describes the background research to these algorithms as well the algorithms themselves, demonstrating their use with ILI dent data from operators of onshore oil and gas pipelines. The paper concludes with comments on the current conservatisms in the analysis of dent fatigue and proposes a way forward to allow pipeline operators to manage large numbers of dents for which the dent fatigue life is critical.
Computing Transmix in Complex Batch Transfers via the Mixing-Volume-Equivalent-Pipe Concept
Authors: de Melo Simone Rodrigues , Freitas Rachid Felipe Bastos
Published: April 2011

This paper presents a new concept — the mixing-volume-equivalent-pipe concept (MVEPC) — which is used to compute transmix volumes in complex batch transfers in an easy, quickly and very simple way. By taking advantage of the MVEPC, the mixing volume of a transfer carried out in a complex pipeline, with varying diameters and flow rates, can be calculated as if it had a unique diameter and a constant flow rate. To illustrate the applicability of the proposed methodology, a numerical example is presented for a transfer of typical products. The transmix volumes predicted by the MVEPC are compared with those obtained by solving the nonlinear initial-value problem for the dispersion of matter parabolic equation. The excellent agreement observed between these two methods, with relative error up to a maximum of 2.65%, enables the use of the MVEPC as a promising tool for estimating transmix volumes in real world batch transfer operations.
Automated Laser Ultrasonic Inspection of Hybrid Laser Arc Welding for Pipeline Construction
Authors: Klein Marvin B. , Ansari Homayoon
Published: April 2011

Hybrid laser arc welding (HLAW) is a technology that promises to increase the efficiency of welded fabrication. By incorporating automation, and integrating an automated inspection system, HLAW can produce high quality welds at higher production rates and lower costs compared to even the most advanced pipeline welding system that is in use today. As the HLAW technique is developed and implemented for pipeline construction, it is important to develop an associated automated technique for weld inspection. We have applied automated laser ultrasonic testing (ALUT) to the important requirement of the in-line monitoring of new HLAW welds in the field. Laser ultrasonic testing (LUT) offers the advantage of true in-process measurement, providing immediate information on weld integrity. In this paper, we will describe our efforts to apply LUT to pipeline girth weld inspection. The technology development process and the integration into an HLAW system will be described.
Effect of Internal Pressure on Free Spanning Pipelines
Authors: Fyrileiv Olav
Published: April 2011

Free span assessment has more and more become an important part of modern pipeline design. The reason for this is partly that the remaining hydrocarbon reservoirs are located in more challenging places, e.g. with very uneven seabed. Another explanation is that the pipeline design codes a few decades ago did not allow for vibrating free spans, while the modern, state-of-the-art pipeline codes, such as DNV-OS-F101 “Submarine Pipeline Systems” (2007) [1] and its Recommended Practices, opens for long spans that are allowed to vibrate as long as the structural integrity is ensured. By opening for longer free spans significant seabed intervention costs associated with trenching, rock dumping and supporting spans by other means are saved. One of the governing parameters to ensure the structural integrity of free spans is the natural frequency of the span. This is a parameter that the designer can to some degree control by means of moderate seabed intervention, e.g. span support. Since the natural frequency of the span together with the water flow velocity normal to the span determine the vibrations and the cyclic loading it is of vital importance to be able to estimate a realistic value of this frequency. The natural frequency is influenced by several effects. One of them is the effect of the internal pressure. This may represent a challenge since the effect of the pressure is the opposite of what one instantaneously thinks is correct. Quite recently some discussion about the effect of internal pressure on free spans were raised and some experimental data presented that claimed to prove that the way the internal pressure was handled in the DNV-RP-F105 “Free Spanning Pipelines” (2006) [2] is wrong. The intention of this paper is to show how the internal pressure influences on the structural response of free spans, and that the DNV codes and standard non-linear FE software, e.g. Abaqus, handle this effect in an adequate manner.
Reality Check on Girth Weld Defect Acceptance Criteria
Authors: Wilkowski Gery , Shim Do-Jun , Brust Bud , Kalyanam Suresh
Published: April 2011

This paper examines the inherent conservatisms of alternative girth weld defect acceptance criteria from the 2007 API 1104 Appendix A, CSA Z662 Appendix K, and the proposed EPRG Tier 2 criteria. The API and CSA codes have the same empirical limit-load criteria, where it has previously been shown that the conservatism on the failure stress is ∼30 to 50 percent compared to pipe test data prior to applying any safety factors. In terms of flaw length, it was found that the API/CSA limit-load equation might allow a flaw of 5% of the pipe circumference, where the properly validated limit-load equation would allow a flaw of 75% of the circumference, i.e., a safety factor of 30 percent on load corresponded to a safety factor of 15 on flaw length for that example case. Similarly there are conservatisms in a proposed EPRG Tier 2 girth weld defect acceptance criterion. This proposed criterion was directly based on curved-wide-plate data to assure that toughness was sufficient to meet limit-load conditions for a curved-wide plate. However, the curved-wide plates are really an intermediate-scale test, and still require proper scaling to pipes of different diameters. The proposed Tier 2 EPRG allowable flaw length is 7T from a large database of curved-wide-plate tests with the a/t value of less than 0.5 (or a < 3mm), and the failure stress being equal to the yield strength of the base metal (also requires the weld metal overmatch the base metal strength, and the Charpy energy at the defect location have a minimum > 30 J and average > 40 J). However, the widths of those curved-wide-plate tests are typically a factor 5 to 12 times less than typical large-diameter pipes. The proper limit-load/fracture mechanics scaling solution would have the flaw length proportioned to the plate width, not the specimen thickness. Additionally, the proper limit-load solution for a pipe in bending gives a much larger tolerable flaw size at the yield stress loading than a plate or pipe under pure tension. Example calculations showed that the EPRG Tier 2 approach is conservative on the flaw lengths by approximately 9 for pure axial tension loading, and between 34 to 79 for a pipe under bending. Suggestions are presented for an improved procedure that accounts for proper limit-load solutions for pipe tests, effects of pipe diameter, effects of internal pressure, and also a much simpler approach to incorporate the material toughness than the 2007 API 1104 Appendix A Option 2 FAD-curve approach. The fracture analyses could evoke SENB, SENT testing, or have relatively simple Charpy test data to assess the transition temperatures to ensure ductile initiation will occur.
From CAD to GIS to the Geoweb: A Natural Evolution
Authors: Adam Steve
Published: April 2011

Computer hardware and software have played a significant role in supporting the design and maintenance of pipeline systems. CAD systems allowed designers and drafters to compile drawings and make edits at a pace unmatched by manual pen drawings. Although CAD continues to provide the environment for a lot of pipeline design, Geographic Information Systems (GIS) are also innovating pipeline design through routines such as automated alignment sheet generation. What we have seen over the past two or three decades is an evolution in how we manage the data and information required for decision making in pipeline design and system operation. CAD provided designers and engineers a rapid electronic method for capturing information in a drawing, editing it, and sharing it. As the amount of digital data available to users grows rapidly, CAD has been unable to adequately exploit data’s abundance and managing change in a CAD environment is cumbersome. GIS and spatial data management have proven to be the next evolution in situations where engineering, integrity, environmental, and other spatial data sets dominate the information required for design and operational decision making. It is conceivable that GIS too will crumble under the weight of its own data usage as centralized databases become larger and larger. The Geoweb is likely to emerge as the geospatial world’s evolution. The Geoweb implies the merging of spatial information with the abstract information that currently dominates the Internet. This paper and presentation will discuss this fascinating innovation, it’s force as a disruptive technology, and oil and gas applications.