Thermal stress monitoring
Thermal stress margin monitoring
Stress in thick-walled component of the boiler result mainly from effects of internal pressure. However permitted stress values in these elements usually are higher, since additional thermal stresses occurring in transient condition should be also taken into consideration. The difference between allowable stresses values and momentary sum of mechanical and thermal stress values is the defined as the thermal stress margin. Due to safety considerations this margin is monitored on ongoing basis.
Thermal stress monitoring requires real thermal stress values to be determined in real-time at all locations monitored in the boiler.
Boiler thermal stress margin monitoring
Thermal stress monitoring module supplements the power plant's diagnostic system. Periodic tests of unit’s thick-walled components material using Non Destructive Examination (NDE) methods permit evaluation of each element’s material exhaustion. The thermal stress-monitoring module described controls correct operation of the equipment between subsequent NDEs.
Material wear indicators monitoring
Power unit’s components operation history affects a material internal structure micro destruction. This causes the material to successively loose its strength properties. Material exhaustion mechanism has been analysed on the basis of experimental results. Mathematic model of the material destruction process allows assessment of material’s current status basing on its operation history.
It is deemed that elements strength depends mostly on two factors: high-temperature creep and low-cycle material fatigue. Both these factors are identified on ongoing basis and its effects are monitored.
Usage factor represents material degradation level in specified period of boiler operation.
Boiler elements exhaustion monitoring
Obtained results of usage factor calculation allow evaluation of material degrading speed compared to recommendations of diagnostic services in power plant, who periodically, every several years, test the current elements exhaustion level.
