Thermal Fatigue - A Quest for Asset Integrity

Introduction

Fired heaters, boilers, and high-temperature equipment require special attention in terms of operation, inspection and maintenance programs due to the unique number of potential damage mechanisms. Even with properly maintained and adequately operated high-temperature pressurized equipment, there have been numerous reported failures that can be attributed to certain unaddressed aspects during operation, maintenance, and inspection.

Fired heaters and pressure vessels operating at high temperatures are subjected to various material degradations and failure modes depending on the operating and environmental conditions, that include but not limited to, temperature, exposure time, material conditions, operating parameters, stress, and repair history. It’s estimated that fired heaters fail more frequently than other static equipment. The inherent design and operational facets of fired heaters make them vulnerable to certain co-acting damage mechanisms that are rarely encountered in other process equipment. In spite of numerous operating and inspection guidelines, recommended practices, and Integrity Operating Windows (IOWs), there are still unanticipated challenges towards the integrity of fired heaters. The various damage mechanisms affecting heaters (e.g., oxidation, fuel ash corrosion, carburization, decarburization, graphitization, spheroidization, short term overheating, thermal fatigue & creep) result from higher operating temperatures (beyond IOW), tube metallurgy, fuel quality, exposure time, environmental conditions, and quality of workmanship.^[1]