A bulging incident happened on the alloy of Fe-Cr-Ni furnace tube after 5 years of operation. The original outer diameter for the tube is 89 mm. The medium environment inside tube is ethane gas. The tube design temperature is 1050oC. The fuel gas has been used to heat the tube containing the ethane gas. The operating heating temperature on the tube is 1044oC. From visual examination, it was found that the bulging is about 0.7mm occurred on the tube. Sigma phase is hard and brittle compound can be formed from austenite at temperature between about 649 to 870oC. The compound approximately FeCr but has a variable composition. The sigma phase imparts ambient temperature brittleness and a loss of creep-rupture strength. The aim is to investigate the formation of gamma phase due to long time working at elevated temperature by using scanning electron microscope and Energy-dispersive X-Ray analyzer.
