Failures caused by UDC occurrence have been reported in the oil and gas industry in various applications. The solid deposits to be addressed in this report are limited to sand, scale, and corrosion products inside pipelines. Wax, asphaltenes, and biofilms certainly affect UDC; however, they are beyond the scope of this report. Accelerated corrosion under iron sulfide and iron carbonate films is thought to cause pitting initiation and propagation in CO2 and H2S containing environments. Pipeline mechanical cleaning becomes a key issue and is usually achieved using aggressive pigging programs on a regular basis. Moreover, corrosion inhibitors have the potential to prevent this type of corrosion, or at least minimize the pigging frequency. It is general practice to establish laboratory testing protocols that are able to assess UDC and evaluate the performance of a given inhibitor in protecting the pipe wall in the presence of solids on the surface.