Detection and estimation of fretting damage in carbon steel and ferritic stainless steel tubes at support plates in shell exchangers

One of the problems that affects tubes in shell exchangers is fretting damage to the tubes where they pass through support plates. Inspection equipment which uses magnetisation of the tube wall to search for defects is a speedy way to locate the damage in carbon steel tubes; pull speeds for the probe are typically over one metre per second. Detection of damage is rarely enough; the size or degree is important. Experimental work has been undertaken on the estimation of damage in carbon steel tubes and has looked at the problems of applying the same technique to ferritic stainless steel tubes. Results of two practical inspections are given and some peculiar features in a ferritic steel-tubed exchanger are described.