Inspeção e reparo de caldeiras de recuperação química em serviço

Abstract

Chemical recovery boilers play a critical role in the pulp and paper production process, serving to recover inorganic chemicals while generating steam for energy production or factory utilities. These complex systems consist of multiple components that experience a gradual loss of strength over time, primarily due to thickness reduction, pitting, and/or cracking in the tubes. These issues are triggered by various damage mechanisms associated with critical factors, including materials, temperatures, contaminants, and operational conditions. Regular maintenance turnarounds involve inspections aimed at detecting and quantifying such damages, which are subsequently evaluated based on their criticality. Of particular concern is the risk of explosion resulting from potential water-smelt contact due to tube leaks in the water wall, superheaters, and screens. The responsibility entrusted to those in charge is exceptionally high, demanding the adoption of conservative measures for damage analysis and repair. In many cases, repairs are performed based on empirical knowledge. The most common repair techniques involve grinding to remove cracks, weld buildup to restore thickness, or replacement of component sections. However, executing these repairs in field conditions poses significant challenges due to limited resources, time constraints, the presence of dissimilar joints, composite tubes with poor weldability, and restricted access, coupled with a lack of design information. This study aimed to develop a comprehensive and practical guide to aid decision-making regarding identified damages in alkali recovery boilers. Furthermore, it aimed to catalog the main repair procedures employed on the boilers' crucial components, based on recognized and generally accepted good engineering practices.