Boiler Tube Long-Term Overheating

This type of failure is usually indicated by a "thick-lipped" burst of the boiler tube. Long-term overheating can result from excessive deposition, flame impingement, mild flow restrictions, or poor water or flue gas circulation patterns.

Probably the most common of these is excessive deposition, which prevents proper heat transfer and excessive metal temperatures. This prolonged overheating of the tube causes metal degradation to the point that in can no longer handle the operating pressure and a "thick-lipped" failure occurs.



 

Long-term overheating usually occurs in superheaters, reheaters and waterwalls  tubes as a result of gradual accumulation of deposits or scale, partially restricted steam or water flow, excessive heat input from burners or undesired channeling of fireside gases. Horizontal or inclined tubes subjected to steam blanketing are also prone to long-term overheating failures. Tube metal operating temperatures above 454C, or slightly above the oxidation limits of the tube steels, can lead to blistering, tube bulging or thick-lipped creep rupture failures .