Study On The Quantitative Risk Evaluation For In-service Condenser With Defects

The first stage condenser of oxidation reactor system is the key pressure vessel in PTA equipment system. It is very important and necessary to evaluate the structure with defects and to predict the residual life and to assess the in-service risk.In this dissertation the stress distribution of C3 butt-joint with misalignment was analyzed by FEA method, fracture safety of C3 weld and C2 weld was evaluated by fracture mechanics, the residual life of condenser was predicted by cycle by cycle method and in-service risk was assessed by the combination method with risk analysis method of API 581 and probabilistic fracture mechanics method. The main conclusions are as follows:(1) Based on the measured data of misalignment, the calculation model was established by ANSYS5.7. From the FEA results, it is found that the maximum stress location was in the maximum misalignment area. For the whole structure, C3 weld is the most weakness location. Under the design pressure, the stress intensity is greater than the allowable stress intensity, which can not be accepted by the standard of JB 4732-95. However, under the operation pressure, the stress intensity is less than the allowable stress intensity, which can be accepted by the standard of JB 4732-95.(2) According to the worst condition modeling, the most serious defect of C3 weld is located between 44~# X-ray film and 52~# X-ray film, which can be expressed as a surface defects with 1220mm in length and 2mm in depth. And there are two most serious defects for C2 weld. One is located between 24~# X-ray film and 34~# X-ray film, which can be expressed as a submerged defects with 1165mm in length and 1mm in depth. The other is located between 68~# X-ray film and 80~# X-ray film, which can be expressed as a submerged defects with 1155mm in length and 1mm in depth. The whole defects were assessed by FAD technology, and the assessment points were all located in the safety area of FAD diagram. Therefore, in the view of fitness for service (FFS principle) these defects can be accepted.(3) Based on the fatigue crack growth rate testing for weldment, it was indicated that the...