An ever increasing demand to exploit oil and natural gas reserves has significantly increased extraction activities even in the remotest regions of the Arctic and sub-Arctic regions of the Canadian North. Steel pipelines are the most efficient mode for transporting and distributing these resources. These pipelines, particularly buried in cold region, often subjected to extreme geo-environmental conditions, where significant inelastic deformation may occur resulting in localized wrinkles. Under continued deformation, there is a possibility of excessive cross-sectional deformation at wrinkle locations, eventually leading to fracture or damage in the pipe wall jeopardizing pipeline safety and integrity . Prior research indicated that occurrence of fracture in pipe wrinkle is rare under monotonic load-deformation process. However, a recent field fracture was observed within the wrinkle location of an energy pipeline. Similar failure mode was observed in a laboratory specimen at the University of Alberta. Both field and laboratory observations had indicated that the final failure was a “tearing” failure at the fold of the telescopic wrinkles resulting from monotonic application of axial load not aligned with pipe axis. This research program was designed to study this specific failure mode and to develop design tool for pipeline engineers. This research started with examining the failed field and test specimens. A preliminary investigation was carried out using nonlinear finite element (FE) model to simulate test and field behaviour. Numerical results have indicated that even under monotonic loading, significant strain reversals could occur at the wrinkle fold . Presence of these strain reversals was proposed as the preliminary failure criterion responsible for this unique failure mechanism. In next phase, a full-scale ‘pipe-wrinkling’ test program was carried out concurrent to this research to better understand the loading condition responsible for this type of failure. Results of this test program have shown the presence of tearing fracture or rupture in the pipe walls of several of test specimens. A series of FE analyses was then carried out to predict and verify the behaviour of these test specimens. After successful simulation of the test behaviour, further numerical analyses were carried out using tension coupon model developed herein to simulate the material behaviour using the material test data and hence to formulate the limiting conditions in terms of critical strain responsible for the tearing failure. Based on these numerical results, a double criterion  ‘Strain Reversal’ and ‘Critical Equivalent Plastic Strain Limit’, were proposed to predict tearing fracture of wrinkled pipe under monotonic loading. Results of these numerical analyses have demonstrated that the proposed criteria predict this failure mode with reasonable accuracy. In the final phase of this research, a parametric study was carried out to consider the effect of different parameters on failure modes of wrinkled pipe. Results of this parametric study describe the range of parameters under which the tearing mechanism can/may exhibit. / Structural Engineering

No description available.

Abstract In a petrochemical plant, to exert economic efficiency and spacing convenience for transporting fluid or gas, the pipelines used in the plant are often buried along the road. The buried pipelines are usually wrapped in the soil that only the guided wave method is a convenient technique to perform the nondestructive testing for the pipelines. However, the viscosity of soil causes the attenuation of the guided wave during the test, the accuracy and the detection distance will then be affected. Thus, the objectives of this thesis are to study the characteristics, such as the detection distance and the refraction signal, of the T(0,1) guided wave when propagating along pipelines wrapped in the soil at different depths. The thesis would be divided into two parts: experiment and numerical simulation. Four different depths, 0.5, 1.0, 1.5 and 2.0 m, are used in the experiment to evaluate the characteristics of reflected signals and its attenuation. Wavelet transform, which would enhance the capability of distinguishing guided wave defect, is used to improve the attenuation of defected refraction signal caused by soil. In the numerical simulation, this research applies the transient simulation by finite element method to analyze the wave propagation behavior of T(0,1) mode guided wave of buried pipeline, which is incorporated with Two-dimensional Fourier transform for modal identification. The result of experiment shows that the attenuation of the guided wave is caused by the leakage and the viscosity of the soil. The decay rate is proportional to the depth and due to the viscosity of the soil is proportional to the excitation frequency. This phenomenon is more obvious when the pipeline is buried deeper. The reflected signal amplitude of each characteristic would decrease along with the increasing soil depth, but the overall trends did not changed. The result of wavelet transform shows that the capability of distinguishing of the guided wave detection defect of buried pipeline, which attenuation of refraction signal caused by soil would be improved. The result of the numerical simulation indicates that the T(0,1) mode would not cause mode conversion and dispersion due to its propagation through the buried pipeline with different depths of soil. The soil caused leakage of the T(0,1) mode in the form of shear waves. The attenuation rate of guided wave and its detection distance in the study could be the reference of site selection for detection and defect refraction signal determination, which could effectively raise the efficiency of on-site detection.

Natural Hazards are a risk to buried gas pipeline infrastructure, but these risks are difficult to assess and quantify. This can often lead to the risks not being properly identified by pipeline owners. The risk to pipelines within landslide areas are particularly difficult to assess given the complex nature of landslide movements and the soil-pipeline interaction mechanisms imposing loads on a pipeline. This thesis research examines the relationship between ground movements and strains/stresses in buried pipelines through field measured ground movements and in-situ measured pipe strains/stresses. The pipe stresses and strains are then used to estimate probability of pipeline failure and risk based on RBDA limit states approaches. Within Manitoba Hydro’s pipeline network, three at-risk landslide areas (riverbank and deep river valleys) were selected for detailed studies. A field investigation and monitoring program was undertaken to assess possible sources of load and stresses on pipelines. Soil, ground, and pipe instrumentation were installed at the sites and monitored over a four year period. Monitoring results identified soil near the pipeline does not freeze, and ground movements at valley sites are slow moving (<50 mm/year) landslides. The monitoring results also showed pipe stresses and behaviour were affected by backfilling, changes in river levels, thermal affects, soil-pipe relaxation, and ground movements. Pipe push tests were conducted in conjunction with FEM modelling to examine pipe adhesion and to possible explain the pipe behaviour observed. Several ultimate and serviceability limit states pipe failure modes were assessed using the measured pipe stresses. Statistical analysis was undertaken to calculate the probability of pipeline failure for the various limit states failure modes and compared against limit states targets for several scenarios (backfill loads, initial stress-state of the pipeline, other pipelines within Manitoba Hydro network). Overall, the probability of failure estimates were generally insignificant or low due to a postulated soil-pipe relaxation mechanism which is causing a repeated release in longitudinal pipe stresses as the landslide continues to accumulate ongoing ground movements. Three mechanisms are presented and discussed. The statistical analysis indicate pipelines within Manitoba Hydro’s network may exceed limit states targets for yielding and local buckling depending on the loading scenario and the class of the pipeline within the landslide area. The outcome of the research was used to develop a risk managements system to examine geotechnical hazards within Manitoba Hydro’s pipeline network. Specifically, risks associated with ground movements along natural slopes and at river crossings are examined within the system. / October 2016

The goal of this study is to develop probabilistically based empirical correlations for seismic performance assessment of buried pipelines. Within the scope of these research efforts, pipeline performance case histories have been compiled from Duzce city after Duzce earthquake. The characteristics of Duzce water supply and distribution system with the earthquake damage on the system were studied. Correlations of the damage patterns with the water distribution system, earthquake and geotechnical characteristics have been developed. Moreover spatial distributions of the earthquake effects havebeen transferred into Geographic Information System (GIS) format. As a result of these studies, it was intended to define the seismic, geotechnical and structural parameters which may explain the spatial variability of the observed seismic pipeline hazard. For the development of such correlations, a maximum likelihood framework for the probabilistic assessment of seismically induced buried pipeline performance is described. A database, consisting of postearthquake field observations of buried pipeline performance after Duzce earthquake in conjunction with in-situ index test results, is used for the development of probabilistically based seismic pipeline performance correlations. As a result of careful processing of available data, the variables of the problem are selected as: liquefaction susceptibility of soil, thickness of soft soil layer if it exists, peak ground acceleration and estimated ground deformations. A limit state function is defined in terms of these variables. Repairs on the pipeline system due to earthquake are compiled with the surrounding soil and earthquake parameters and the correlations of pipeline performances with the mentioned variables are determined. Different sets of fragility curves are developed for seismic pipeline performance problem, representing various sources of uncertainty that are intrinsic to the problem. Such information is believed to be useful to utility system operators in planning a seismic retrofit or upgrade program for existing pipeline systems.

Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-01-31 20:52:11.162 / One of the most severe hazards for buried pipelines, which are sometimes referred to as lifelines due to their essential role in delivering vital resources, is the hazard due to Permanent Ground Deformation (PGD). Earthquake induced PGD can be caused by surface faulting, landslides and seismic settlement. In this thesis, the behaviour of buried pipelines subject to normal faulting has been experimentally investigated through a series of centrifuge tests performed on both continuous and jointed pipelines. Both pipe and soil displacements were measured using image analysis. Signal processing techniques were then developed to filter this data so as to enable the calculation of curvature and other aspects of the response from the observed pipe deformations. First, a series of centrifuge tests was conducted on continuous pipelines of varying materials, representing a wide range of pipe stiffness relative to the soil and investigating the effect of pipe stiffness relative to the soil on soil-pipe interaction. The experimentally derived p-y curves at different locations along the pipe were compared to the recommended soil-pipe interaction models in the relevant guidelines. These p-y curves showed that the central shearing region was not captured well with independent soil springs. The response of the pipelines predicted by the ALA (2001) guideline, however, was shown to match the experimental data within 50%. Two new simplified design approaches were then developed. The first features calculations based on simplified pressure distributions. The second featured peak curvature normalized using a characteristic length, ipipe, the distance from peak to zero moment. A series of centrifuge tests using brittle pipes was also performed. The pipes were buried at three different depths, and the post-failure fracture angle of the pipe was measured to be used as an input for design of liners. Based on the experimental data, a computationally efficient approach was developed to estimate the initial fracture angle which occurs immediately after the pipe breaks. The last series of centrifuge tests was conducted on jointed pipelines with five different joint stiffnesses to investigate the flexural behaviour of jointed pipelines under normal faulting. Based on the observed pipe response, a simplified kinematic model was proposed to estimate the maximum joint rotation for a given geometry, pipe segment length, and the magnitude of the imposed ground displacement. / Ph.D

Perante diversas situações da engenharia são utilizadas formulações empíricas de dimensionamento baseadas em dados de campo e experiência profissional que definem muito o caráter subjetivo da metodologia padrão de projeto. O presente trabalho de pesquisa aborda os diversos métodos de obtenção dos esforços gerados em dutos enterrados submetidos a cargas dinâmicas e estáticas e sua posterior reavaliação através de modelagem numérica com o programa Plaxis 3D. Os métodos analíticos não convencionais foram comparados com o método padrão de cálculo sendo que o mesmo demonstrou ter uma boa precisão mesmo sem considerar outros fatores importantes como a parcela de resistência devida à coesão do solo e sua deformabilidade. A modelagem numérica demonstrou o conservadorismo do método de Marston e o subdmensionamento do espraiamento em prisma devido aos efeitos locais ocasionados pela adoção do recobrimento mínimo e sobrecarga dinâmica elevada. Também se observou, através da modelagem 3D, que a utilização dos dois métodos clássicos favorecem a obtenção de resultados dentro da razoabilidade.Verificou-se também, como resultado desta pesquisa, que a proposta de um método clássico modificado permite uma melhor aproximação da carga que atinge o duto. / In various engineering situations, empirical formulations of design, based on field data and professional experience which highly define the subjective nature of the standard design methodology, are used. This paper discusses the various methods of obtaining the stresses generated in buried pipelines, which are subjected to static and dynamic loads, and their subsequent re-evaluation by numerical modeling with Plaxis 3D program. The non-conventional analytical methods were compared with the standard method of calculation and it has demonstrated good accuracy even without considering other factors such as soil cohesion and deformability. The numerical modeling demonstrated the conservatism of the Marston method and subsiding of the prism spread due to local effects caused by the adoption of minimum cover and high dynamic overload and due to how the use of two classical methods favor reasonable results. A classic modified method that would allow a closer approximation of the load was also proposed.

Perante diversas situações da engenharia são utilizadas formulações empíricas de dimensionamento baseadas em dados de campo e experiência profissional que definem muito o caráter subjetivo da metodologia padrão de projeto. O presente trabalho de pesquisa aborda os diversos métodos de obtenção dos esforços gerados em dutos enterrados submetidos a cargas dinâmicas e estáticas e sua posterior reavaliação através de modelagem numérica com o programa Plaxis 3D. Os métodos analíticos não convencionais foram comparados com o método padrão de cálculo sendo que o mesmo demonstrou ter uma boa precisão mesmo sem considerar outros fatores importantes como a parcela de resistência devida à coesão do solo e sua deformabilidade. A modelagem numérica demonstrou o conservadorismo do método de Marston e o subdmensionamento do espraiamento em prisma devido aos efeitos locais ocasionados pela adoção do recobrimento mínimo e sobrecarga dinâmica elevada. Também se observou, através da modelagem 3D, que a utilização dos dois métodos clássicos favorecem a obtenção de resultados dentro da razoabilidade.Verificou-se também, como resultado desta pesquisa, que a proposta de um método clássico modificado permite uma melhor aproximação da carga que atinge o duto. / In various engineering situations, empirical formulations of design, based on field data and professional experience which highly define the subjective nature of the standard design methodology, are used. This paper discusses the various methods of obtaining the stresses generated in buried pipelines, which are subjected to static and dynamic loads, and their subsequent re-evaluation by numerical modeling with Plaxis 3D program. The non-conventional analytical methods were compared with the standard method of calculation and it has demonstrated good accuracy even without considering other factors such as soil cohesion and deformability. The numerical modeling demonstrated the conservatism of the Marston method and subsiding of the prism spread due to local effects caused by the adoption of minimum cover and high dynamic overload and due to how the use of two classical methods favor reasonable results. A classic modified method that would allow a closer approximation of the load was also proposed.