In Situ Metallography Applications in the Pipeline Industry

Abstract

The Merriam-Webster Dictionary defines metallography as “a study of the structure of metals, especially with the microscope.” The structure of a steel visible at high magnification can reveal information about how the steel was formed or heat-treated, the general “quality” of the steel, whether any observed discontinuities originated during manufacturing or while the component was in service, and the extent to which properties may be consistent across the wall thickness. Microstructural features such as grain size, the amount and distribution of inclusions, and the types and amounts of different microstructural phases are known to influence a material’s properties. In some cases, the observed attributes are qualitatively characterized. In other cases, manual or digital image analysis facilitates quantitative descriptions of attributes such as grain size, the percent of a selected phase, or inclusions that are present. Typically, small sections are cut from the pipe or other component and metallographic sample preparation and examination are performed in a laboratory. When destructive sampling is impractical, the specimen preparation, visual examination, and related photo documentation can be performed nondestructively in the field. That process is known as “in situ metallography” and is the subject of this paper.