Análise de falhas de tubos de uma caldeira aquatubular

Abstract

The petroleum refining activity depends on water vapor in several of its processes. The water vapor used in refineries comes from boilers, which are equipment designed to produce and accumulate water vapor at pressures above atmospheric pressure. In combustion boilers, high pressures and temperatures present are factors that increase the susceptibility to damage that can lead to loss of production, high costs and accidents. The present work deals with a case study of the analysis of tube failures in the furnace of a water-tube boiler installed in an oil refinery. Water leaks, changes in the values of the parameters observed in the supervisory system and water vapor coming out of the equipment chimney showed ruptures in the furnace tubes of a boiler of the unit. These tubes showed localized swelling, fouling on the inside and severe oxidation on the outer surface. In view of this, visual inspection methods, hardness testing, metallographic examination and physical-chemical analysis of the boiler feedwater were carried out in order to obtain a better understanding of the mechanism that generated the failure and, from there, to prevent further occurrences. The results of the analysis of the methods show that the tubes failed due to the combination of creep and oxidation at high temperatures, due to the direct incidence of flames and reduction of the thermal exchange caused by the presence of incrustations, resulting from inadequate water treatment. Actions taken to mitigate the problems proved to be ineffective, indicating that inadequate water treatment is the root cause, because by causing incrustations in the pipes, it reduces the thermal efficiency of the equipment, so that a greater input of heat is necessary for the production of steam at the required levels. In this way, the incidence of flames in the pipes occurs, further aggravating the damage and accelerating the encrustation process, configuring a highly destructive vicious circle.