Gamma-ray tomography instrumentation for investigating carbon steel pipe corrosion under insulation

This thesis details a non-destructive type of tomographic technique to monitor corrosion under insulation. This method requires a radioactive source, where a detector-source pair is mounted on a circular gantry located around the periphery of a steel pipe. A radioactive source with an appropriate activity was chosen based on the thickness of the pipe under test. In order to detect gamma rays, photon scintillation detectors are required. A Thallium-activated Sodium Iodide (NaI(Tl)) detector crystal was used. Stability tests were conducted on the detectors before they were ready to be used. A portable hardware to house the detector and source was then designed and built. The system is able to operate without the need for an outlet socket to enable it to be used in remote locations where power supply may be unavailable. For testing purposes, artificial corrosion defects were created by grinding the surface of the pipeline under the insulation by a minimum of 2 mm in depth and by placing foreign objects (wood splinters and pebbles) under the pipeline insulation. A modified parallel beam sensor geometry was implemented to measure the intensity of the incident beam after passing through the pipeline under test. The Backprojection method of tomogram reconstruction without the need for sensitivity matrices was used. The software written generates three tomograms, which are the ideal pipe tomogram, the tomogram of the pipe under test and the error tomogram which compares the first two tomograms and then highlights in red the suspected corrosion under insulation. The system was able to achieve an average accuracy of 96.283% when a comparison was done between actual dimension of the objects under test and the dimension based on the intensity profiles. The error tomogram constructed was able to detect and highlight artificial corrosion of a minimum of 2 mm in depth

Development of a distillation column scanning apparatus using gamma-ray tomography

Process column and reactor scanning apparatus are process diagnostics instrumentation and is required to be brought to the plant and used by specialized personnel. Radioisotope gauges have been used for this type of measurements for more than 50 years, and is still widely used. Data is normally recorded for subsequent off-line analysis. Often multiple measurements are carried out in a scan for instance by manually lowering a source down one side of a vessel and a detector down the other to build up a vertical density profile. A trained operator can then easily interpret this signature and provide information on the state of the process as well as the process vessel

New sensor design for capacitance tomography

Any two adjacent conductors can be considering as a capacitor, and different dielectric properties between the conductors will create different capacitor value. An ECT system is able to obtain information about the contents of vessels, based on measuring variations in the dielectric properties of the flowing material inside the vessel. ECT can be used with vessels of any cross-section, but most work to-date has used circular geometries (Malcolm Byars, 2001)

The experimental study and numerical simulation of falling liquid film flow on horizontal tubes

This research is motivated by two observations: No report has been found so far in studies of water falling film up to 100 mm intertube spacing. No simulation analysis of film thickness under influence of intertube spacing in 3 dimensional models. Therefore, to the best of author’s knowledge, this research aims to illuminate the effects of intertube spacing between horizontal tubes on water falling film. An experimental investigation of water falling film temperature was conducted to explore the characteristics of heat transfer coefficients. In this study, the intertube spacing from smallest size of 8 mm and up to 100 mm were analyzed for Reynolds number range of 300 to 3300. The experimental data was extracted from calibrated test rig and the effect is investigated using numerical study. On the other hand, the effect of film thickness is numerically investigated for intertube spacing range of 10 mm to 40 mm. The numerical simulation was presented using the Volume of Fluid (VOF) technique where it is capable in determining temperatures and thickness of water falling film under influence of ambient factors. The experimental results reveal that intertube spacing of 133 mm produced the maximum heat transfer coefficient of 6 kW/m² K with percentage of error below 7%. The results of the numerical simulation indicate that the 40 mm intertube spacing presented the minimal average film thickness of 0.3 mm within ± 50% errors. Implications of the results and future research directions are also presented

Hardware development of electrical capacitance tomography (ECT) system with capacitance sensor for liquid measurements

Electrical capacitance tomography system is useful for obtaining information about the spatial distribution of a mixture of dielectric materials inside a vessel. This research aims to obtain real-time monitoring on the composition for liquid mixture in conveying pipeline. ECT is a non-invasive, non-intrusive and non-destructive technique that can measure the flow level inside a pipeline. In order to increase the image resolution and accuracy of current tomography research, a study on 16 electrodes sensor ECT system has been developed. The developed system has the flexibility to be assembled and moved from a pipeline to another. The intelligent on-board flexibility and mobility sensor technique is a new technique for ECT system. The system can be assembled in different diameter sizes of pipeline, and numbers of electrodes sensor can be reduced accordingly depending on the pipeline sizes without the need to redesign the electrodes sensor. The new design is equipped with high speed data processing rate data acquisition system and high speed data reconstruction. A microcontroller that support full-speed USB data transfer rate has been designed as the centralization control unit. In order to improve data result, iterative algorithm has been implemented in this system in order to obtain a precise image of the flow in the pipeline. As a result, the ECT system is able to reconstruct various multiphase flow image

Stability test for NaI(TI) scintillation detector

The objective of this endeavor is to present a brief description of a stability test performed on a NaI(TI) scintillation detector to determine its most suitable operating voltage range. The Chi-square test is used to check the reliability of the data obtained. Some test results are included

Mobile electrical capacitance tomography (ECT) development for liquid-gas flow measurement

Electrical capacitance tomography (ECT) system is useful to obtain information on spatial distribution of dielectric material mixture inside a vessel. This paper discusses a sixteen-electrode mobile ECT sensing system which is developed non-invasively and non-intrusively. Emphases on the software development aspects are presented in several sections; initialization part, normalization part, calibration part, hardware communication part and the image reconstruction part. Thus, the liquid-gas concentration profile of the ECT system is successfully acquired using the software developed

Introduction to gamma-ray transmission tomography

Conventional gamma ray computed tomography methods measure the attenuation of an incident beam that travels in a straight path through an object. The incident beam is partially absorbed and scattered in the object of interest, with the remaining transmitted radiation traveling in a straight line to the detector. This is the principle of gamma -ray transmission tomography. The amount of attenuation is related to the atomic number of the phases distributed in the object, as well as their density distributions. As with radiography, access to both side s of the structure is required. Any changes in the transmitted intensity to the adjacent detector will reflect the change s of the mass per unit area of the material

Image reconstruction study utilizing ultrasonic transceiver

Currently, besides ultrasonic there are a number of tomography techniques available for studying complex multiphase phenomena. These include electrical tomography (Impedance, Capacitance and Resistance), optical, positron emission tomography (PET), X-ray, magnetic resonance imaging (MRI), ultrasonic and others. Each of these techniques has its advantages , disadvantages and limitations but each of it has common purpose to analyze measured data. The best way is by reconstructing images from acquired data. Process tomography consists of tomographic imaging of systems, such as process pipes in industry. In tomography the cross sectional image distribution of so me physical quantity in the object is determined. There is a widespread need to get tomographic information about process. This information can be used, for example, in the design and control of processes. Tomography involves taking measurements around the periphery of an object such as process vessel to determine what is going on inside