Pipeline Research Council International Research Articles

Failure pressure estimation for an aged and corroded oil and gas pipeline: A finite element study

The mechanical behavior of an aged pipeline, affected by localized and generalized corrosion defects, is investigated using the finite element method. A sample of pipeline steel was aged artificially via an isothermal process (which represents the natural aging transformations), to obtain the mechanical characteristics. In real scenarios, oil and gas pipelines undergo deterioration owing to both aging and corrosion defects.Therefore, this research studies the assessment of failure pressure by combining these two types of deterioration using the finite element method. To calibrate the methodology proposed for estimating the pipeline failure pressure,data from real-scale burst tests published by the Pipeline Research Council International (PRCI) was used. Following the simulations, the initial failure region for each type of defect was determined and analyzed. Similarly, the estimated values of pipeline failure pressure were compared to assess the results obtained through finite element analysis, considering the changes in mechanical characteristics caused by the artificialartificial aging of the steel. In addition, these results were compared with those of certain well-known semiempirical models. Finally, for the different types of corrosion defects investigated in this study, the effects of volumetric loss on the estimation of pipeline failure pressure using finite elements are discussed. The main conclusion of this study is that failure pressure can be estimated more accurately by considering both corrosion defects characteristics and variations in the steel properties caused by aging.

Estimation of tensile strain capacity for thin-walled API X70 pipeline with corrosion defects using the fracture strain criteria

Various tensile strain capacity (TSC) prediction equations have recently been presented by many research organizations such as Pipeline Research Council International and ExxonMobil Corporation. The gas industry uses these equations to determine the allowable strain for the cracked pipe. However, these TSC prediction equations cannot be applied to pipes with other defects such as corrosion or mechanical damage. Corrosion defects are the most common type of defect in actual operating conditions, and thus, they are an essential element for evaluating pipe structural integrity as they are most frequently connected to accidents. Therefore, it is necessary to develop a TSC prediction equation for corroded pipes. In this paper, to propose a new TSC prediction equation for corroded pipes, we conducted parametric finite element (FE) analyses using fracture strain criteria. To determine the appropriate fracture strain criteria, we reviewed several methods to construct the fracture locus. Then, we conducted parametric FE analyses using this fracture locus by considering variables affecting structural integrity, such as corrosion depth, corrosion length, wrap angle, and pressure ratio. Lastly, we presented the TSC prediction equation using these analyses.

PRCI ambient NO2 AERMOD performance assessment and model improvement project: Modeled to observed comparison

ABSTRACT On January 22, 2010, the U.S. Environmental Protection Agency (EPA) established a new one-hour probabilistic National Ambient Air Quality Standard (NAAQS) for nitrogen dioxide (NO2) at 100 parts per billion (ppb) or approximately 188 micrograms per cubic meter (µg/m3). The 1-hr NO2 NAAQS is considerably more stringent than the longstanding annual standard of 53 ppb or approximately 100 µg/m3. AERMOD is the EPA recommended dispersion modeling tool for predicting impacts from emission sources, including compressor station reciprocating engines. Existing datasets were previously reviewed to evaluate and improve AERMOD 1-hr NO2 model performance. However, these datasets were not representative due to either an absence of accurate concurrent hourly emission inventories, being associated with larger electric generating units, shorter duration tracer studies, or were too site-specific (e.g., external influences such as terrain). To address this data gap, an intensive 13-month field data program was undertaken by Pipeline Research Council International (PRCI) to collect a comprehensive dataset including concurrent emissions, meteorological, and ambient ozone and nitrogen oxide measurements. This paper describes the Balko, OK natural gas compressor station host site and the design of the meteorological, ambient NOx and O3 monitors and continuous Parametric Emissions Monitoring System (PEMS). Two comparisons are made between the monitored data and AERMOD results. First, the measured onsite data (ambient air, meteorological, and emissions) were used as input to AERMOD to make comparisons between measured and modeled NOx and NO2. These comparisons showed that NOx was both over and under predicted, sometimes beyond a factor-of-two. The second comparison uses the typical permitting approach where onsite data are not available to contrast how conservative input assumptions for emissions, background O3, NO2, and offsite meteorology cause significant over predictions especially for this site where engines have a low annual utilization rate and operate infrequently throughout the year. Implications: This project resulted following the promulgation of the new 1-hr NO2 NAAQS and the challenges that natural gas pipeline compressor stations have in modeling intermittent emissions using AERMOD to demonstrate compliance with this standard. AERMOD was developed and validated with a primary focus on large sources with tall stacks, such as electric utility boilers. A recently collected dataset at a gas compressor station in Balko, Oklahoma shows that the use of permitted allowable emission values compared to actual hourly emission values causes over predictions using typical regulatory methods. Comparison of model results using actual hourly emission values to coincident ambient air monitoring values at the site shows that AERMOD over predicts near-field impacts due to simplifying assumptions including building downwash, plume dispersion, chemistry, and 1-hr invariant meteorological conditions.

Numerical analysis of pipeline response to slow landslides: case study

A numerical analysis is carried out to study the behaviour of pipelines subjected to slow landslides at three at-risk landslide zones of Manitoba Pipeline Network. The pipeline’s longitudinal axis is parallel to the slow landslides at all three research sites. The ground displacements monitored for 5 years are imposed on the pipe using a special purpose pipe–soil interaction element (PSI element) using ABAQUS/Standard. The stiffness of PSI elements is defined based on soil–pipe interface properties according to a 2017 technical report from Pipeline Research Council International Inc. The results of the numerical analysis are compared with the instrumentation data to draw recommendations for future monitoring programs in slow landslide zones.

Experimental evaluation of the effect of the internal pressure and flaw size on the tensile strain capacity of welded X42 vintage pipelines

Pipelines exposed to geo-hazards such as moving slopes, discontinuous permafrost, and other ground movements may be subjected to displacement-controlled loading, which may lead to significant plastic strains. This can potentially impact pipeline structural capacity and their leak-tight integrity. Traditional stress-based design methods may become uneconomical in the design of pipelines subjected to large plastic strain. In view of the extensive use of such pipelines, reliable calibration of the tensile strain capacity (TSC) plays a critical role in strain-based design (SBD) methodology. Recent studies were focused mostly on high toughness modern pipelines with limited research performed on lower-grade vintage pipelines. However, the effects of biaxial loading due to internal pressure and bending stresses imposed on pipelines as a result of interactions with geo-hazards were not properly addressed in previous studies. This paper investigates the effect of internal pressure and flaw size on the TSC of X42 welded vintage pipelines using experimental testing. Eight full-scale pressurized four-point bending tests were conducted on 22 inches (558.8 mm) diameter X42 grade welded vintage pipes with D/t ratio of 44 to examine the effect of the influential parameters on the TSC. Biaxial strain gauges and a digital image correlation (DIC) system were major instrumentations used for measuring strain. The results were used to examine the crack growth rate by estimating the crack mouth opening displacement (CMOD) at failure and the effects of internal pressure and flaw size on the TSC. The TSC obtained from the tests were compared with those predicted using TSC predictive models proposed by ExxonMobil and Pipeline Research Council International (PRCI).

The drone’s got a nose for methane

Unpiloted aircraft, or drones, can sniff methane from hundreds of meters away from the source, making them promising sentries for early detection of natural gas leaks, say researchers from NASA; the University of California, Merced; and the Pipeline Research Council International, an organization of energy pipeline companies. The team announced last week that a 1.7-kg drone known as a quadcopter detected parts-per-billion levels of methane thanks to a miniaturized open path laser spectrometer. Such sensitivity is key to identifying—from the sky—small leaks from natural gas pipelines or storage facilities, says team member Lance Christensen, a chemist at NASA’s Jet Propulsion Laboratory. The sensor’s laser excites methane molecules as they trickle into the instrument, creating measurable disturbances in the optical signal. Ultimately, a network of drones could monitor natural gas infrastructure around the clock, but researchers will need to optimize the detection system first, Christensen says. For example, the team is

A Warehouse of Defective Pipe

Pipe repository What looks like a collection of rusty old pipes in a Houston warehouse is a repository of carefully selected objects cared for as if they were part of a museum. Inside and out of the warehouse, there are tubulars once buried in the ground or laid on the ocean bottom. There are large sections of tubulars with corrosion damage inside and out, dents, tiny cracks, and failed welds. The collection is at the center of research and development (R&D) work by the Pipeline Research Council International (PRCI), which established the location in Houston in December 2011 to house a growing collection that had been scattered in odd spaces at companies around the world. There are more than 150 examples of real-world pipe selected because they fit into the group’s programs, which are dedicated to developing ways to ensure that pipelines are safer and more reliable, said Mark Piazza, director of pipeline programs for PRCI. For Steve Banks, product development manager at Genesis Oil and Gas Consultants, this ordinary-looking warehouse is like a “toy cupboard.” It offered him access to one-of-a-kind objects needed to test the progress of a project to commercialize a device being developed by Genesis at its R&D facility at the University of Manchester. What stands out about the new machine is its ability to inspect pipes whose inner walls are covered by waxy buildup or other gunk. The pipe repository is a tangible sign of the PRCI’s technology development program that users say has helped them get past barriers that are often a dead end for new ideas in the oil business. PRCI members provided advice to Genesis on what the device needed to do, funding support of 2 years of prototype development access to the repository, where Genesis could evaluate its progress on pipe samples with defects known only to a few within PRCI. “The process is fantastic,” said Banks. “Over a 3-year cycle, we are taking something sitting under a sink in a lab, developing it, patenting it, and deploying it in the field with real live data.”

Effect of Geometry, Material, and Pressure Variability on Strain and Stress Fields in Dented Pipelines Under Static and Cyclic Pressure Loading Using Probabilistic Analysis

Mechanical damage in transportation pipelines is a threat to their structural integrity. Failure in oil and gas pipelines is catastrophic as it leads to personal fatalities, injuries, property damage, loss of production, and environmental pollution. Therefore, this issue is of extreme importance to pipeline operators, government and regulatory agencies, and local communities. As mechanical damage can occur during the course of pipeline life due to many reasons, appropriate tools and procedures for assessment of severity is necessary. There are many parameters that affect the severity of the mechanical damage related to the pipe geometry and material properties, the defect geometry and boundary conditions, and the pipe state of strain and stress. The main objective of this paper is to investigate the effect of geometry, material, and pressure variability on strain and stress fields in dented pipelines under static and cyclic pressure loading using probabilistic analysis. Most of the published literature focuses on the strain at the maximum depth for evaluation, which is not always sufficient to evaluate the severity of a certain case. The validation and calibration of the base deterministic model was based on full-instrumented full-scale tests conducted by Pipeline Research Council International as part of their active program to fully characterize mechanical damage. A total of 100 cases randomly generated using Monte Carlo simulation are analyzed in the probabilistic model. The statistical distribution of output parameters and correlation between output and input variables is presented. Moreover, regression analysis is conducted to derive mathematical formulas of the output variables in terms of practically measured variables. The results can be used directly into strain based assessment. Moreover, they can be coupled with fracture mechanics to assess cracks for which the state of stress must be known in the location of crack tip, not necessarily found in the dent peak. Furthermore, probabilities derived from the statistical distribution can be used in risk assessment.

Gas Storage and Operations in Single-Bedded Salt Caverns: Stability Analyses

Summary Bedded salt formations are located throughout the U.S., providing valuable storage capacity for natural gas and other hydrocarbons. To increase gas-storage capabilities and provide operators with improved geotechnical design and operating guidelines for these caverns, stability analyses of single-bedded salt caverns have been completed and are described in this paper. This work is a part of integrated efforts initiated and sponsored by the U.S. Department of Energy (DOE), the Gas Technology Institute (GTI), and Pipeline Research Council International, Inc. Numerical geomechanical models have been developed to investigate single-cavern deformation and bedding-plane slip for a variety of cavern configurations. A viscoplastic salt model has been developed based on an empirical creep law developed for the Waste Isolation Pilot Plant (WIPP) Program and combined with a Drucker-Prager model for damage and failure. The nonsalt materials are described with either a traditional Mohr-Coulomb model, or an elastic model, depending on layer properties. A baseline model with specified geometric dimensions is first selected and subjected to 1-year cyclic pressure operations. The amount of damage around the cavern wall and roof is evaluated and used as a comparison in the study. Then, the operations are extended to 15 years to study cavern stability for long-term gas storage and operations. In addition to the baseline model, parametric studies have been performed to investigate cavern damage as a function of salt roof thickness, overburden stiffness, interface properties, and cavern geometries. Each cavern simulation includes 1 year of pressure cycling with a minimum, mean, and maximum cavern pressure of 6.1 MPa (884.5 psi), 8.8 MPa (1,276 psi) and 14.9 MPa (2,160.5 psi), respectively. Different operation conditions (e.g., hydrostatic, cyclic, and direct-pressure drawdown) are compared and evaluated in terms of cavern stability. These analyses can be a basis to selecting the best salt cavern candidate for gas storage and operations as well as helping to assess critical cavern design parameters for thin-bedded salt formations.