Original old petroleum trade magazine vintage article titled ONSTREAM INSPECTION and Corrosion Control by H.C. Bozeman, Gulf Coast Engineering Editor.  

A plant inspector routinely inspects a unit while it is operating at full rates.  There are two main type  of inspections.  One is a corrosion-analysis survey, the other a conditional survey.  Ultrasonic, radiographic, and visual measurements are made on hot lines while units are in operation.  Visual inspection is still the most widely used and versatile way for finding extent of external corrosion. Radiographs of small connections are shown at a refinery using extra-heavy nipples between the pipe and first valve.  

1962 fourteen page gatefold oil and gas industry article.