Journal of Pipeline Systems Engineering and Practice

The researchers at Ohio University examined various aspects of the buried plastic pipe-soil interaction problem through their thermoplastic pipe deep burial project. This paper addresses one issue that they have not studied before—the modulus of soil reaction of the backfill materials. This modulus is a key parameter of the buried pipe-soil system. However, it has rarely been determined from actual field data. Most engineers and researchers consult publications such as AASHTO specifications or the values reported in the American Water Works Association design manual when selecting its value for any given flexible pipe installation case. A careful analysis made on the deep burial project data showed that the field-based soil modulus values were close to the published values for dense granular backfill materials. For loose granular backfill materials, the field-measured values were higher than those provided by the AASHTO specifications and laboratory one-dimensional compression test results. Other findings of the analysis included the following: (1) no straightforward one-to-one correlation was observed between the relative compaction level and the soil modulus; and (2) the soil stiffness gauge readings could not represent the actual soil modulus values seen in the buried thermoplastic pipe problems.

At present, advanced numerical models of pipelines crossing active faults are based on the representation of the pipeline as an ensemble of shell or solid finite elements. The surrounding soil is represented as an inelastic continuum using appropriate constitutive models and three-dimensional (3D) solid elements. The pipeline-soil interaction is modeled as a surface-to-surface contact problem. These models allow a detailed analysis of the stress-strain state with account for localized limit states to be performed. Still, concerning the lack of data from real seismic events and large-scale tests, which can be used for calibration of numerical models, the question of adequacy of the numerical results is a topical issue. In this paper, a 3D numerical model of a buried steel pipeline crossing an active tectonic fault is developed and discussed with an emphasis on the pipeline-soil interaction and mathematical representation of the fault. The influence of the fault model on the predicted stress-strain state of the pipeline is analyzed using two different types of fault representation. The first approach is based on the continuous representation of the fault; in the second approach, two separate soil blocks interacting along the fault plane are introduced. The latter approach has not yet been applied to the analysis of fault-crossing problems. The numerical results are compared on the basis of displacement, strain and contact soil pressure distributions, evolution of the pipe ovalization parameter and bending moment in the critical cross section, and soil deformations in the near-fault zone.

Offshore oil and gas pipelines are commonly buried in seabed to provide environmental stability, thermal insulation and mechanical protection. These pipelines are frequently subjected to high thermal and pressure loadings that induce pipeline upheaval buckling (UHB). The uplift resistance provided by the cover soil increases with pipeline upward mobilization and reaches its peak at peak mobilization. This peak mobilization is fundamental for safe UHB designs. This paper highlights that the design guidelines underestimate the peak mobilization. The paper presents full-scale uplift results and finite-element parametric studies in which loose and dense cover soils of up to 3 m (soil cover height to diameter ratio up to 15) and pipeline diameters of 114 and 200 mm were investigated. Results from full-scale and finite-element modeling show that the peak pipe mobilization can be much greater than that suggested by current guidelines, and it is a function of the soil cover height to diameter ratio and soil relative density. A new relationship is proposed to predict peak mobilization from the soil cover height to diameter ratio for a given soil state.

A nondestructive technique based on indentation and enhanced by the consideration of the imprint mapping is proposed for the diagnostic analysis of pipelines in oil transportation systems. The considered testing procedure can be applied in the field without the need of extracting spools and working out the specimens required by more traditional experimental approaches. The reliability of the presented methodology is verified by investigating a pipe segment with more than 25 years of service. The mechanical properties determined by indentation and imprint mapping compare well with the output of standard tensile tests in average terms while better insight on the spatial distribution of the material characteristics is achieved.

Prestressed concrete cylinder pipe (PCCP) is a composite pipe structure commonly used for high-pressure water transmission. If these pipes deteriorate, they can cause a water main break, which can cause extensive property damage and compromise the potable water system. Accordingly, there has been considerable interest in developing reliable nondestructive evaluation (NDE) techniques capable of identifying damaged pipes prior to rupture. In the current study, a series of finite-element and experimental studies are undertaken to establish the groundwork for an acoustic resonance–based NDE method capable of characterizing the earliest stage of deterioration in PCCP associated with damage to its outermost layer.

The decisions made during the preproject planning and design stages are very crucial for infrastructure and underground projects due to the inherent risks and uncertainties in such projects. In the selection of a crossing method, the owner has to consider various factors, including cost, environmental impact, serviceability and maintenance, constructability, and schedule. Unfortunately, this decision is complex due to the numerous variables that need to be considered. When choosing a crossing methodology, the project manager must balance the likely capital cost of the project with the risks inherent in the chosen construction method. Ideally, a project manager would investigate numerous alternatives to fully explore the merits of various construction methods, including the level of risk, before making the final decision. This paper presents the results of an actual project workshop with the objective of selecting the most optimum construction method for the construction of a water transmission main beneath the North Saskatchewan River, in Edmonton, Alberta, Canada. The project used the analytical hierarchy process as a method to capture the risks, merits, and demerits of each construction method. Conventional open trench, horizontal directional drilling, microtunneling, and conventional tunneling were the four methods considered for the project. The paper includes the background information, workshop setting, methodology of the selection criteria, and the results of the workshop considered in selecting the most optimum method for the specific project circumstances. A summary of the design based on the recommended methodology is also presented along with a summary of the crossing construction completed in 2007.

First, a methodology was proposed for predicting the remaining life of buried gas pipelines subject to corrosion and cyclic loads. Variation in corrosion-defect depth was considered an exponential function of pipeline elapsed time, and the cumulative damage rate was employed to compute pipeline cyclic damage. Because of the presence of nonlinearity in the formulas, an iterative method was used for calculating remaining life and total damage of pipelines with field data. Next, a limit-state function based on remaining-life mode was adopted for estimating pipeline failure probability, and the associated random variables were represented by normal probabilistic distributions. Then the acceptable failure probability and risk interval were combined for assessing pipeline reliability, which was validated with field data.

There is evidence in literature that friction factors smoother than smooth, that is smaller than the ones obtained by the Moody/Prandtl/White Colebrook/Nikuradse smooth pipe law (or Blasius law), have been measured in large diameter pipes. It is shown that a slight amount of rotation or swirl, caused, for example, by a bend, may persist in a straight pipe, thereby reducing the apparent friction factor as calculated with the nominal Reynolds number. If the friction factor is calculated with the actual Reynolds number, taking into account the rotation, the Blasius law may remain valid. The reduction in friction factor is typically of the order of 5 to 10% for rotation numbers smaller than 1 to 2. The phenomenon is likely to appear only in large diameter pipes and/or at high Reynolds numbers.