Posted by Carl on April 19, 2000 at 16:03:59:
In Reply to: Root Cause of Tube Failure posted by Ken Nisly-Nagele on April 18, 2000 at 06:48:10:
: What are steps to determine root cause of tube failure in a once through water tube boiler? Can metallurgical analysis provide useful answers? Can swelling/blistering of tubes be caused by impact of steam from nearby leaking tube or is it from problems prior to leak event?
In a once through boiler the normal flows if disturbed by blockage, either by scale or circulatory problems may induce film boiling in regions normally wetted. If tube metal temperature has resulted in a loss of metal strength it can result in bulging. Agreed that near by tube leaks normally would wash the tube and result in errosion of the adjacent tubes not blistering. A metalurgical examination can be done on tube specimens to determine the grain growth and help you to understand the temperatures the metal was subjected to. However, one interesting case I was involved with happened just after startup from a cold start after an outage. A piece of material was left in the lower header in the front wall and when the unit was fired off it was sucked up against the tube opening in the header and resulted in a single failed tube from fish mouth rupture. Not that this information would help but thought to send you my two cents worth. Basically in a nut shell, yes tube analysis is a good start to determine the amount of possible deposits and metal condition on failure.
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