Pendant-style reheater, constructed of ASME SA-213, grade T-11, steel ruptured. A set of four tubes, specified to be 64 mm OD x 3.4 mm minimum wall thickness was examined. A small quantity of loose debris was removed from the inside of one of the tubes. The major constituent was revealed by EDS analysis of the debris to be iron with traces of phosphorus, manganese, sodium, calcium, copper, zinc, potassium, silicon, chromium, and molybdenum. Thus the debris was interpreted to be the scale from ID of the tube with boiler feedwater chemicals from the attemperation spray. The likely cause of failure was concluded to be exfoliation of the scale from the ID surface of the tube. Creep failures were interpreted to be caused by localized temperatures higher than the maximum service temperature. Replacement of the affected tubes was recommended. Inspection of the tubes by radiography to find the circuits with the greatest accumulation of debris and replacing them as necessary was recommended on an annual basis.

The principal types of elevated-temperature mechanical failure are creep and stress rupture, stress relaxation, low- and high-cycle fatigue, thermal fatigue, tension overload, and combinations of these, as modified by environment. This article briefly reviews the applied aspects of creep-related failures, where the mechanical strength of a material becomes limited by creep rather than by its elastic limit. The majority of information provided is applicable to metallic materials, and only general information regarding creep-related failures of polymeric materials is given. The article also reviews various factors related to creep behavior and associated failures of materials used in high-temperature applications. The complex effects of creep-fatigue interaction, microstructural changes during classical creep, and nondestructive creep damage assessment of metallic materials are also discussed. The article describes the fracture characteristics of stress rupture. Information on various metallurgical instabilities is also provided. The article presents a description of thermal-fatigue cracks, as distinguished from creep-rupture cracks.

A pressure vessel failed causing an external fire on a nine-story coke gasifier in a refinery power plant. An investigation revealed that the failure began as cracking in the gasifier internals, which led to bulging and stress rupture of the vessel shell, and the escape of hot syngas, setting off the fire. The failure mechanisms include stress relaxation cracking of a large diameter Incoloy 825 tube, stress rupture of a 4.65 in. thick chromium steel shell wall, and the oxidation of chromium steel exposed to hot syngas. The gasifier process and operating conditions that contributed to the high-temperature degradation were also analyzed and are discussed.