Safety Assessment Of Pressure Piping With Incomplete Penetration Defects In Ammonia Refrigeration System

The pressure pipes are widely used in various industries,which have a large number and distribute widely,and they are easy to cause safety accidents.If the pressure pipes leak or explode,it will lead to a lot of economic and people's live lost.Therefore,it has important engineering application value to research on the defect prediction,failure analysis and safety assessment technology of the pressure pipes.The safety management of the pressure of pipes in China is still in the initial stage,the overall technical force is relatively weak,and the pressure pipes are usually welded with manual welding way,it will leave various defects in weld lines.Especially for the pressure pipes in ammonia refrigeration system,a large number of incomplete welding defects are found during on-site inspection,these pipes are assessed as grade 4 according to the current assessment specification,and they must be repaired or scrapped.But almost no leakage or explosion accidents happened for these pressure pipes with incomplete welding defects during their service time,so how to deal with the pressure pipes with incomplete welding defects must be solved urgently.For pressure pipes containing incomplete welding defects,the safety assessment method based on limit loads analysis was suggested in this paper.The typical pressure pipes in ammonia refrigeration system were assessed by this method,and the improvement measurements were also put forward.The main research contents and results are as follows:(1)The defect types of the pressure pipe in ammonia refrigeration system were summarized,and the rule to process the incomplete welding defects was simplified.The main failure modes of pressure pipe in ammonia refrigeration system were analyzed,and the safety assessment method and procedure based on the brittle fracture failure mode and plastic limit load failure mode were put forward.(2)The finite element models for the typical pressure pipes in ammonia refrigeration system were developed,and detailed stresses of the pipe lines were analyzed,the safety of the pressure pipes were assessed based on brittle fracture model and plastic limit load failure mode.The evaluation results show that there are 4 out of 9 pressure pipes can not meet the safety requirements.(3)For the pressure pipes which can not meet the safety requirements,the improve measurements to increase pipe wall thickness or adjust pipe hanger were suggested.