Occasional failure of a lining, is an inevitable consequence of the application process, the properties of the material, and the severity of service. The consequences of failure include loss of product, process down time, and repair costs. A recognized or suspected failure with significant economic impact may require a formal investigation and analysis. This paper describes the three stages of an investigation including a site visit, laboratory analysis of samples, and assessment and recommendations. Detailed site and laboratory procedures are described, along with examples of the purposes and typical findings. The processes of determining the most likely cause of failure and of recommending resolution is described with several case histories.