Review of materials property data for nondestructive characterization of pipeline materials

The oil and gas industry relies on an aging infrastructure of pipeline for transportation and distribution of product; therefore, it is important to assess the condition of the pipeline, using accurate material and mechanical properties, to ensure failures are minimized. Nondestructive evaluation techniques are currently being used to assess pipeline, but necessary mechanical properties (yield strength, tensile strength, fracture toughness, and ductile-to-brittle transition temperature) are not yet able to be adequately characterized by these methods. There are many issues to consider when addressing this problem. There is variability within the manufacturing processes due to simple inaccuracies in the processes themselves, and changes in practices over the years. There is also variability in the destructive techniques used for assessment of mechanical properties before the pipe is put into service. Current focus in the industry tends to be on pipe installed in the 1950’s and 1960’s because about half of the pipe currently in service was installed during these time periods, but it is equally important to verify the properties of modern pipe Therefore, nondestructive methods of measurement are commonly used for determining defect severity (e.g. magnetic flux leakage and ultrasonic) are being explored to determine what other properties can be measured to relate to mechanical properties. For future activities, it is advised to compare the accuracies of both destructive and nondestructive methods of determining properties, should some method of nondestructive evaluation become a more viable technique for mechanical property measurements, either directly or indirectly. The relationships between what can be measured (chemical content, grain size, microstructure, hardness, coercivity, permeability, etc) and the mechanical properties desired listed previously, show that there is a strong relationship between hardness and yield strength. This is already well known in the industry. Other important relationships to evaluate further include the percent content of various alloying elements, most notably including manganese and carbon in relation to the yield strength, fracture toughness, and grain size. Magnetic properties such as permeability and coercivity are also important, as these showed stronger correlations within research, but are not available in the available sample data set. In this thesis, research has been performed to establish the current state of the art, highlighting some of the areas of difficulties in terms of obtaining consistent data sets. Linear correlations were performed on the sample data available to observe the results for yield strength and fracture toughness determination. Similar characteristics were also compared to historical studies and generally the conclusions were well reflected by both data sets. For future study, it would be of use to obtain saturation, permeability, coercivity, and remanence measurements on the sample data to see if the correlations are similar to what was developed shown in historical studies. Additionally, creating a chart of the various ultrasound measurements such as velocity, attenuation, and backscatter grain noise could open up more insight as to how effective ultrasonic measurements are in determining the desired mechanical properties. From this information, the potential for application of nondestructive methods of evaluation prove to be beneficial in supporting the pre-existing destructive methods, and eventually developing for field application