This paper presents results of the failure analysis of carbon steel screen tubes and cyclone cans for separation of wet steam. Site inspection showed severe abrupt multiple bulges with a hole on the top of first screen tube with a thickness of 3.5 mm (0.14 in.) and OD of 76.2 mm (3.0 in.). The investigations found that the cleanliness of the tubes should be considered as “very dirty”. In other cases, the carbon steel cyclone cans with thickness of 3 mm (0.12 in.) were gradually thinned and completely perforated only in the front portions located opposite to the wet steam inlet. The results of metallographic, X-ray and SEM/EDS analysis are presented and discussed. It was found that the screen tubes failed due to creep rupture as a result of local overheating caused by the presence of excessive amounts of deposit. Cyclone cans mainly experienced severe impingement type of damage. Remedial actions were recommended in each case and were implemented.
Keywords: Boiler, screen tube, cyclone can, creep, tube cleanliness, impingement.