How long can refining equipment be used after it becomes brittle?
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There are currently no standardized residual service life criteria for refining equipment after brittle failure; such criteria can only be determined through professional safety assessments. The key factors for making such judgments are as follows: First, a compliance assessment must be carried out. In accordance with the API 579 suitability evaluation (FFS) standards, along with on-site metallographic inspections, impact toughness tests, and non-destructive testing results, it is necessary to determine the extent of the brittle failure damage and assess whether the equipment meets the requirements for pressure safety. Reference service life for different scenarios: If the degree of embrittlement is mild and the material’s impact toughness remains within acceptable limits, it can be operated for a short period under strict monitoring by restricting the operating pressure and temperature; in such cases, a safe service life of several months to 1–2 years can generally be achieved. If embrittlement has caused microscopic cracks and a significant reduction in toughness, with no safety margin left, the equipment must be stopped immediately and replaced; it must under no circumstances be used any longer. Some of the hydrogenation furnace tubes show signs of embrittlement due to slight carbide precipitation; after evaluation, they can operate under specified conditions for several years before being replaced during the scheduled maintenance cycle.
The assessment process shared by the original poster is very professional; the FFS evaluation according to API 579 is indeed recognized as the industry standard. I would like to add two details that are easily overlooked in practical operations: Monitoring indicators need to be quantified. If the assessment result indicates \"mild brittleness and short-term operability,\" it is recommended to specify the critical values for daily monitoring (such as the lower limit for impact energy and the upper limit for crack growth rate), rather than relying solely on intuition to decide that everything is fine. If possible, online acoustic emission monitoring would be more reliable. Boundary conditions for short-term operation: The original poster mentioned pressure and temperature limits; in practice, the number of cycles also needs to be taken into account—frequent start-stop operations or pressure fluctuations can accelerate crack propagation. It is recommended to include the \"allowed operating cycles/temperature-pressure combinations\" in the operating instructions to prevent errors by the operators. I would also like to remind the original poster and all colleagues that judgments regarding the lifespan of pressure-bearing equipment must ultimately be based on formal reports issued by inspection agencies with the appropriate qualifications. Discussions on forums are intended solely for technical exchange and cannot replace decisions made regarding safety on site.