Monitoring of risks based on early diagnostics of equipment and structures metal state in stress concentration zones - the sources of damages development

摘要

Currently, the deterministic approach is mainly used in risks assessment during operation of hazardous industrial facilities (HIF). Assessment of emergencies probability is carried out based on the available statistics of damages accumulated over the past period of HIF operation. Such approach is imperfect and insufficiently objective as risks are assessed for the future period of time, when the technical condition of HIF may change significantly, and fatigue damages of individual equipment components may occur (and, as a rule, they occur) in areas that do not coincide with those estimated. It is known that the main sources of equipment and structures damages are stress concentration zones (SCZs), in which metal corrosion, fatigue and creep processes develop most intensively. SCZs are not only the areas known ahead, where the structure features create various conditions for distribution of stresses due to external work load, but these are randomly located areas where large strains occurred due to initial inhomogeneity of the metal structure combined with off-design additional work loads. In the course of experimental studies it was found that the level of stress in local SCZs ranging in size from tens of microns to a few millimeters can significantly exceed not only the yield strength, but also the tensile strength of the metal. The experience of 100% inspection of various pipelines, structures and rotating machinery equipment using the magnetic memory metal (MMM) method shows that only 5 to 10% of the total equipment metal volume encounters the development of damages in SCZs after its long-term operation. The MMM method allows to perform in the express control mode early diagnostics of damages in these areas, lifetime prediction and risk assessment.