Evaluation and Assessment of a Superheater-Tube Elbow in a Coal-Based Power Plant Boiler after 10 Years of Operation

Inspection of each piece of equipment is required as part of a power plant-reliability program. Detailed procedures and assessments are developed based on standard or best practices in the power industry. For an accurate assessment, an understanding of the damage mechanism is crucial. In this work, a study was conducted on a superheater-tube elbow to evaluate its thinning mechanism to develop an assessment guideline. The thinning of the tubes was evaluated after 10 years of operation by sampling the tubing in 90° and 180° elbows that represent standard elbows in a power plant. Macroscopic observation, ultrasonic measurement, and chemical and metallurgical analyses were conducted. The analyses showed that although oxidation and erosion occurred, the rate was relatively insignificant at the time of sampling. In addition, analytical and finite-element analyses were performed to assess the stress level under various thickness scenarios. This work demonstrated that a separate investigation is necessary to determine the minimum wall thickness and replacement schedules for superheater-tube-elbow inspection.