Analysis of failed reformer tubes

Reformer tubes from a fertilizer plant made of modified HK 40 steel which failed after 4 years service were investigated for failure mechanism and life evaluation. The investigation included hot tensile tests, hardness measurement, dimensional measurement, microscopy and a few accelerated creep tests. Analysis revealed that longitudinal cracks found in the tubes were caused by overheating because of inadequate feed flow caused by the choking of damaged catalyst. To avoid such choking, precautions should be taken while charging the catalyst that no broken piece of catalyst or any external material goes along. Nitrogen which is used for cooling down the tubes and which was retained inside during idle periods should be dry enough. Overheating during service is primarily responsible for significant degradation in mechanical properties and microstructures in the bottom portion of the reformer tubes.