Evaluating ultrasonic tomography (UT) methods used for the inspection of offshore pipelines

Abstract

In the oil and gas industry, safe and trustable operations of a pipeline system need guidelines for operations and maintenance. These guidelines should be used to optimize the operations by improving product output and uniformity, lower the input process requirements, decrease the energy consumption and environmental impact and lower the number of plant personnel. Real-time process monitoring also plays an essential role to provide efficient operations by providing quantitative data as accurately as possible and by consideration of hydrodynamic parameters like flow regime and flow rate. We will suggest that imaging and measurements of the pipeline content in order to inspect can be achieved by an ultrasonic tomography system. One of the challenges that we might be faced with in these regards is the barrier at the seafloor, which makes some disturbance for sensors in order to monitor the pipeline. It could also be difficult to mount the ultrasonic tomography array appropriately. The occurrence of a complex sound field, that causes overlapped or multiple reflected pulses, is another impediment that leads to further errors. Furthermore, there is a significant problem in using ultrasonic tomography as we use metal pipes, because the ultrasonic energy is attenuated dramatically in metal, and there are the large effects of Lamb waves. If we, however, achieve an appropriate technique of the ultrasonic tomography system for flow sensing, we will be able to monitor flow disturbance inside the pipe. Here, we suggest that a non-invasive ultrasonic tomography system is feasible; that is, we suggest that the offshore industry will solve the challenges of monitoring. This will involve cooperation between two teams composed of; 1. Physicists, chemists and subsea specialists (to create an efficient sensor system and to mount and implement the sensors), 2. As well as computer programmers (to provide cross-sectional images of the objects inside the pipelines, identifying and profiling debris and also wall metal loss at the same time and provide a snapshot of the flow regime). The objective of this thesis is to describe the technique of non-invasive ultrasonic transducers, and investigate how ultrasonic waves propagate in the pipeline flow field. For this purpose, there will be emphasis on the ultrasonic tomography techniques; a description of ultrasonic waves, how they propagate. Subsequently the use of the non-invasive ultrasonic tomography method in offshore pipelines will be discussed. After obtaining the relationship between the ultrasonic waves’ propagation and their frequencies, a perception of non-invasive ultrasonic tomography in the subsea pipeline and the development of installation application will be considered.