Journal of Pipeline Systems Engineering and Practice

This paper addresses the problem of specifying, estimating, and validating Weibull hazard rate models for water distribution networks under incomplete data. The most notable advantages of the proposed model are the ability to incorporate expert opinion and the spatial analysis of break histories in order to improve the predictive performance of the model with respect to identifying the highest risk cohorts of pipe. The methodology was demonstrated on a large utility in the southeast United States. The expert opinion of utility professionals was elicited to fill in data gaps associated with pipe material; categorical variables were introduced to account for the bias associated with such data imputing. Additionally, a kriging model was used to estimate the spatial distribution of pipe break rates on subsets of the network, and the resulting break rate parameter was added to the Weibull model. Validation metrics showed that including both the parameter estimates and break rate parameter increased the model’s capability of identifying pipe groups with the highest risk of failure. These results show that utilities with limited known parameters describing pipe networks can elicit additional data through expert opinion and spatial analysis to develop prioritization models for repair, replacement, and rehabilitation.

In the last two decades, stormwater chamber products have become popular in the United States and other countries for managing stormwater. These products are typically arch-shaped and light-weight for efficient transportation, handling, and field installation. Despite the popularization of the products, currently there is a lack of rational analysis/design methods for these structures. Also, with little effort to establish industry standards, these chambers come with various raw materials, wall designs, and cross-sectional shapes. In this paper, a software package was used to perform a series of two-dimensional numerical simulations of both single and multiple chamber systems installed in the ground. Based on the simulation results, several key issues related to stormwater chamber structure were discussed, such as the optimum cross-sectional geometry, failure modes, and chamber spacing. Computer simulation results were also viewed in light of observations made during recent field loading tests. Main conclusions reached in the study are that (1) the arch-shaped chamber structures, having either semicircular or elliptical cross-sectional shape, are capable of sustaining a high level of external loading by distributing the stresses to the surrounding soil columns; and (2) the foot region of the chamber appears to be critical and needs special attention.

Accurate and rapid detection of leaks is important for subsea oil pipelines to minimize environmental risks and operational/repair costs. Temperature-sensing optical fiber cables can provide economic, near real-time sensing of leaks in subsea oil pipeline networks. By employing optical time domain reflectometry and detecting the Brillouin scattered components from a laser source, the temperature gradients can be detected at any location along an optical fiber cable attached to the oil pipeline. The feasibility of such technology has been established in the literature along with a case study on a land-based pipeline. In this paper the accuracy of an optical fiber-based temperature sensing system is investigated. A mathematical model that simulates the process of temperature sensing is developed and the results are presented. An experimental investigation is carried out with two different laboratory setups to establish the spatial resolution and accuracy of the optical fiber cable detection system, and the experimental results are compared with predictions from the theoretical model. Based on these comparisons it has been established that the optical fiber cable detection system is capable of providing an accurate and rapid assessment of the location of a leak along a subsea pipeline. Furthermore, the sensing system can be used to give an indication of the scale of the oil leak using the temperature gradients detected by the system.

The objectives of this study are to evaluate the parameters that affect the behavior of flexible pipes for culverts and storm sewers and to examine the strength-limit states of such pipes proposed by the AASHTO bridge-design specifications. The flexible pipes investigated in the study are high-density polyethylene (HDPE), PVC, and metal pipes. The pipe diameters considered are 914 mm (36 in.) and 1,219 mm (48 in.). A three-dimensional finite-element (FE) model has been developed to simulate the behavior of buried pipes under truck load. Results from field tests conducted by the authors for large-diameter pipes under $2D$, $1D$, and $0.5D$ burial depths, where $D$ is the pipe diameter, were used to evaluate the accuracy of the numerical model. Extensive parametric studies were then carried out to examine the effect of burial depth, backfill soil quality, and compaction level on the buried pipes, and their results are reported in this paper. The effect of these parameters has been evaluated in terms of thrust values at the pipe shoulder and springline, vertical diameter changes, and longitudinal strains. Regression analysis was carried out based on the FE model predictions for the first load pass and on results from a research study available in literature to predict the behavior of buried pipes with multiple load passes. The parametric study has shown that the performance of buried pipes varies with the soil type, and the increase of compaction level and soil cover reduces the stresses on buried pipes. The numerical predictions indicate that the provisions of AASHTO bridge-design specifications for HDPE pipes need to be reassessed for very shallow burial depths.

Solid particles can be transported along a pipeline in the form of trains of individually shaped lenticular deposits (LDs) when the concentration of solids is less than 1 vol% and the transport velocity is below the critical value required for full suspension. Such special bed transport, observed as rippled sand dune patterns, may occur in petroleum production lines transporting oil and gas produced from unconsolidated sand reservoirs under turbulent flow conditions, and during sediment transport by rivers and winds. The primary objective of this study was to investigate how the occurrence of lenticular bed deposits affects near-wall turbulent activities at the sand/fluid (“wave-like”) interface and frictional pressure drop during pipeline transportation of solids. Particle image velocimetry (PIV) measurements were used to quantify the velocity field, the turbulence kinetic energy (TKE), and the coherent structures associated with surface morphology change and LD formation near the bed deposits/fluid interface. A 7–8% reduction in frictional pressure drop was consistently observed during the transition from continuous sand bed to LDs. Results also indicate that the formation of naturally shaped LDs reduces the intensity and frequency of near-wall turbulent coherent structures (burst-sweep events). Moreover, TKE associated with flow over the LDs was found to be lower than that of continuous bed and water (only) flow.

A failure investigation was conducted on a 30.5-cm diameter gray cast iron water main that failed in Anchorage, Alaska, due to a longitudinal fracture. Nearby pressure transducers recorded very modest system pressures at the time of the failure and the pipe did not show signs of advanced graphitization or significant mechanical damage. Mechanical testing and microanalysis were performed on the pipe material. The cause of the failure was determined to be brittle fracture which initiated at a subcritical corrosion fatigue (CF) crack approximately 40.6 cm in length. The corrosion fatigue crack nucleated from a casting defect on the inside surface of the pipe. The findings of the research reported in this paper suggest that subcritical CF crack growth may be a threat to gray cast iron water pipes. Corrosion fatigue mechanisms in gray cast iron have not been documented previously and may be a contributing factor for anomalous fractures showing evidence of multistage failure.