Internal Pipe Wall Research Articles

Transient heat transfer in a coaxial borehole heat exchanger

Ground-source heat pumps often use vertical boreholes to exchange heat with the ground. A transient heat transfer model has been developed for a thermal response test on a pipe-in-pipe coaxial borehole heat exchanger. The analytical model calculates the vertical temperature profiles in the fluid flowing through the pipes, which are coupled to the surrounding grout and ground. The model is verified against measured vertical temperature profiles in the circulating fluid during a distributed thermal response test. The comparison with measured data indicates that the proposed model gives a more accurate estimate of the borehole thermal resistance than the conventional analytical model that uses a mean temperature approximation. The model demonstrates how strongly the shapes of the temperature profiles are dependent on the thermal resistance of the internal pipe wall and the flow direction.

Sizing limits of metal loss anomalies using tri-axial MFL measurements: A model study

A model study of the length and width sizing capabilities of the three components of the magnetic flux leakage (MFL) as used for inline inspections of pipelines is presented. The accuracy and limitations of the length and width sizing of metal loss anomalies are investigated using analytical results of the dipole model for the magnetic flux leakage of cuboidal anomalies. For anomalies (in particular metal loss) located at the internal pipe wall the accuracy of the length and width sizing is much better than for external anomalies. This is due to the fact that internal anomalies are located closer to the MFL sensors and thus are less smoothed in the measurements. In general the best results for the sizing are achieved using the radial component. The model results suggest that a further increase of both, the axial and circumferential resolution of current MFL tools can improve the sizing capabilities for internal anomalies, especially for internal pinholes. For external anomalies no significant improvement can be expected by increasing the axial sampling.

Biodeterioration of asbestos cement (AC) pipe in drinking water distribution systems

Various types of microorganisms have been found to inhabit the inner surfaces of asbestos cement (AC) pipe and their activities can cause significant structural damage. They cause a patina to form on the inside surface of AC pipes as a distinctively continuous coating, commonly 2–5 mm in thickness and generally pigmented as yellow, orange, brown or black depending on the metallic cations that have been incorporated into the surface of biofilm (bioaccumulation). Four sublayers can be identified in the patina, from the outer sublayer that directly interacts with the conveyed drinking water to the inner sublayer that is in proximity of the intact cement matrix. The microbes in the outer sublayer are composed mainly of inactive biomass that separates the aerobic environment of the flowing water from the anaerobic conditions inside the patina. The bacteriological community structure shifts from mixed heterotrophic bacteria (HAB), iron-related bacteria (IRB) and slime-forming bacteria (SLYM) in the outer layer, to a more diverse community with IRB, acid-producing bacteria (APB) and SLYM and HAB in the middle sublayer, and further to the SLYM dominated in the inner sublayer. By directly interacting with cementitious materials, including generating organic acids, IRB and APB play important roles in the leaching of free lime and the dissolution of calcium (Ca)-bearing hydrated components of AC pipes, creating porous structure and reducing the pipe strength. Scanning electron microscopy with an energy dispersive X-ray has revealed that bacterial activity on the internal AC pipe wall had resulted in a significant loss of hydrated cement matrix, which can cause pipe failure when stresses imposed on the pipe exceed the remaining pipe strength.

Application of unidirectional flushing in water distribution pipes

In this study unidirectional flushing (UDF) was conducted to improve the effectiveness of deposit removal from internal pipe walls and to provide information on pipe networks to enable operators to implement flushing in field. Four ductile cast iron pipes with epoxy-lined and cement-lined were selected for the practice of UDF. Water pressure was measured using a data logger equipped with a pressure gauge. The normal flow velocities of the networks were found to be 0.12 m/sec or below in the study area. Flushing velocities ranged from 1.07 m/sec to 2.78 m/sec by using a blow-off valve for discharge. The discharged water was taken in five-minute intervals to measure water quality parameters: turbidity, residual chlorine, pH, temperature and conductivity in the field; metals, inorganic ions, total suspended solids and heterotrophic plate count bacteria in the laboratory. The practice of periodic UDF as preventive maintenance is expected to contribute to enhancement of safety and stability of the water supply. It was indicated that part of the biofilm could be removed with the sediments in the pipe by UDF since the removal of HPC bacteria was correlated with total suspended solids (TSS) (R2=0.90). The coefficient of determination (R2) between turbidity and TSS is 0.90 except for one outlier. Sediment removal could be estimated from the turbidity data of flushed water in the field using the equation of the relationship between turbidity and TSS.

Computation of strength reliability of a straight section of a trunk gas pipeline

An algorithm for probability computation of the strength reliability of a straight section of a trunk gas pipeline, where the ultimate strength of pipe steel, internal gas pressure, temperature difference, and pipe wall thickness are normally distributed, has been developed.

Experimental Study of the Pipeline Lubrication for Heavy Oil Transport

Heavy oil is accessible in different areas around the world in large amount. Unfortunately its high viscosity makes it difficult to produce and to transport. In this article we focus on transport problems. Pressure drop in the pipes must be lower as possible to limit pump power and to be able to transport in long distance. In the case of heavy oil, the high viscosity leads to huge pressure drop that makes it impossible to simply pump the fluid in single-phase flow, even of large diameter. Different solutions have been developed to transport heavy oil in pipeline like dilution of the crude oil in a lighter one. In this study we experiment a solution that do not modify the viscosity of the oil phase but transform the flow regime of transport: pipeline lubrication. Pipeline lubrication is a technique based on core-annular flow regime and used for pressure drop reduction in the transport of very viscous products. A thin water film adjacent to the internal pipe wall lubricates the internal oil core leading to a longitudinal pressure gradient reduction. An experimental study has been carried out where the influence of the different parameters, which could affect the lubrication process, has been optimised, using water as the annulus and heavy oil as the core of the flow. The tests were conducted in steady laminar flow at moderate flow rates. The results, obtained with annular water injection at the pipe wall, show a pressure drop reduction over than 90% as compared with the same product in flow without lubrication. These results confirm the effectiveness of the lubricating process for heavy oil transport. We also showed that density difference is responsible to particular evolution of the pressure drop with the flow rate.

Evaluation of inverse algorithms in the analysis of magnetic flux leakage data

We evaluate the use of linear and nonlinear inverse algorithms (maximum entropy method, low resolution electromagnetic tomography, L/sub 1/ and L/sub 2/ norm methods) in the analysis of magnetic flux leakage (MFL) measurements commonly used for the detection of flaws and irregularities in gas and oil pipelines. We employed MFL data from a pipe with well-defined artificial surface breaking flaws at the internal and external wall. Except for the low-resolution electromagnetic tomography, all algorithms show, on average, similar accuracy in the flaw extent estimation. Maximum entropy and the L/sub 1/ norm have a tendency to yield better results for smaller flaws, while the L/sub 2/ norm performs slightly better for larger flaws. The errors of the flaw location estimation are comparable for the maximum entropy and the L/sub 2/ norm algorithm. The L/sub 1/ norm performs worse for those flaws situated on the internal pipe wall. Linear methods (L/sub 2/ norm) are easier to implement and require less computation time than nonlinear methods (maximum entropy method, L/sub 1/ norm). In conclusion, inverse algorithms potentially provide a powerful means for the detection and characterization of flaws in MFL data.

Field and material-specific simulated distribution system testing as aids to understanding trihalomethane formation in distribution systems

The evolution of disinfection by-products (DBP) in drinking water is triggered at the initial point of disinfectant application and, in most cases, continues to some extent throughout the distribution system. A comprehensive study using an extensive field monitoring program, together with an improved simulated distribution system (SDS) test, is presented, in which the effects of increased chlorine demand exerted by internal pipe walls are included in the evaluation of potential DBP exposure to the public. In the field study, comparing both pre-formed trihalomethane (THM) and THM formation potential among several distribution system locations eliminated inherent uncertainties associated with the complexities of network hydraulics, leaving exposure to the internal pipe environment as the primary factor of interest. Findings in this paper confirm the reliability of using the material-specific SDS (MS-SDS) test as a better representation of DBP evolution in a real distribution system. In the case study, the increased chlorine demand of unlined cast-iron results in lower levels of trihalomethanes than those dictated by testing the finished water alone. The MS-SDS test is readily adaptable for pilot-plant studies where real distribution system conditions are inaccessible.Key words: chloroform, disinfection by-products, distribution systems, field monitoring, simulated distribution system.

Diagnostic Techniques for Sewer Systems

The National Research Council Canada has recently completed a project to assist the city of Montreal in determining the condition of its water and sewer system. The National Research Council Canada staff members reviewed available and developing diagnostic techniques for both systems, conducted experiments on nondestructive evaluation methods and provided general scientific advice during the course of the project. This paper presents a review of current technologies for inspecting brick, concrete, and vitrified clay sewer systems, including the results of three experimental investigations. The results of the review are given in a tabular form that lists the applications, advantages, and disadvantages of each technique. Current and developing technologies are described that will supplement or replace closed circuit television inspection for determining the condition of sewer pipes through inspection of their internal pipe walls. In addition, techniques that allow sewer operators to investigate the pipe wal...

Vibro-acoustic response of a pipe excited by a turbulent internal flow

This article presents an experimental study of the vibro-acoustic response of a pipe excited by a fully-developed turbulent air flow. First, the wall pressure field acting on the internal pipe wall is investigated. The power spectral density of the wall pressure fluctuations is analyzed after cancellation of contaminating background noise. The convection velocity and correlation lengths are calculated from measured cross-spectra, and the cross-spectra are expressed in Corcos model form. Second, the vibro-acoustic response of the pipe is analyzed by referring to the structural modes of the pipe.

A magnetic flowmeter with conducting pipe wall for expanded field of applications

The internal pipe wall of magnetic flowmeters should be non-conductive to prevent generated electromotive force from short-circuiting. Usually the inside of metallic pipe is lined with insulating material. The lining limits applicable temperature range of measured fluid and also its reliability. A new structure is proposed, in which the insulating liner is eliminated. A potential distribution is formed on the pipe wall by applying voltage proportional to fluid flowrate. The potential distribution is kept almost identical to the flow-induced potential in the fluid so that no current flows across the boundary between fluid and wall. Therefore the output signal is exactly the same as that of conventional magnetic flowmeters.

導体管壁をもつ電磁流量計

The internal pipe wall of magnetic flowmeters must have been non-conductive to prevent generated electromotive force from short-circuiting. Usually the inside of metallic pipe is lined with insulating material. The lining limits applicable temperature range of measured fluid and also its reliability. A new structure is proposed, in which the insulating liner is eliminated. A potential distribution is formed on the pipe wall by applying voltage proportional to fluid flowrate. The potential distribution is kept nearly identical to the flow-induced potential in the fluid so that no current flows across the boundary between fluid and the pipe wall. Therefore the output signal is exactly the same as that of conventional magnetic flowmeters. In this paper theoretical analysis and experimental results are described.