Nondestructive metallographic examination of materials frequently must be performed on-site when the component in question cannot be moved or destructively examined. Often, it is imperative that specific microstructural information (i.e., material type, heat treatment condition, homogeneity, etc.) be obtained either before initial use of a component, or before the use of a component can be safely resumed. In this paper, the use of standard metallurgical laboratory equipment, and the procedures required to conduct nondestructive on-site metallographic analyses of engineering materials, is presented. As an example, the materials and metallographic techniques employed in an actual on-site investigation of a gas tungsten-arc weldment joining two large diameter Ti-6Al-4V alloy cylinders are discussed in depth to illustrate what can be accomplished.

An evaluation of indications in the main turbine building column horizontal plate welds was conducted by the joint efforts of field metallography and nondestructive examinations. The turbine building main column horizontal plate welds were selected at random and were inspected to find discontinuities, metallurgical evaluation of the discontinuities, analysis of any failure modes, and determination of the best repair techniques. The welds were made with prequalified joints in accordance with AWS D1.1-77 and required only visual inspection. More sensitive inspection methods were applied to the welds in order to better define the indications found with the visual inspections. Cracks were found in 17 field welds and in two test plate welds. The causes of the cracking are related to the weld design and installation procedure. Three field welds were rejected because of the depth of the cracks. The NDT inspections, evaluations, method of field metallography, analysis and conclusions are discussed with recommendations for corrective actions in the following report.

Stress-corrosion cracking of low-alloy steel turbine discs has emerged as a generic concern in nuclear generating stations. An investigation that made extensive use of field metallographic techniques to examine suspected cracking in such a component is described. The crack position, and its relationship to surface topographic features, were examined and recorded by magnetic rubber and high-resolution dental rubber replicating materials. Corrosion deposits on keyway surfaces and within the crack were collected with acetate foil replicas applied and then stripped from the keyway surfaces. Microstructural details were revealed by the use of field metallographic preparation techniques and replicated by acetate foil for examination with optical and scanning electron microscopes. It was possible by these techniques to establish the cracking mechanism as stress corrosion possibly related to chloride or sulphate ion steam contaminants. Subsequent sectioning and conventional metallography confirmed both the validity of the conclusions and the replication techniques.

This article provides a discussion on the metallographic techniques used for failure analysis, and on fracture examination in materials, with illustrations. It discusses various metallographic specimen preparation techniques, namely, sectioning, mounting, grinding, polishing, and electrolytic polishing. The article also describes the microstructure examination of various materials, with emphasis on failure analysis, and concludes with information on the examination of replicas with light microscopy.