Study On The Risk Based Maintenance Plan For Ethylene Cracking Furnace

Tube cracking furnace is the important equipment in the field of chemical, petrochemical and chemical fiber industry. In the running of cracking furnace, the furnace tube tends to creep and carburize under high temperature and pressure. The cracking furnace is of high risk in the olefin production plant. Therefore, it is very important to make maintenance plan for cracking furnace. The subject of this dissertation is the study on the risk-based maintenance plan for ethylene cracking furnace. The cracking furnace E-BA1103 is the object of research. This dissertation applies risk based maintenance to formulate maintenance plan for cracking furnace based on different risk of components. The main contents of present dissertation are as follows: 1. With the Failure Model and Effect Affect (FMEA), the failure reasons and its effects are made sure. According to inspection & maintenance records and design documents, the maintenance strategy of cracking furnace with the Reliability Centered Maintenance (RCM) was generated. Different maintenance levels are classified as safety, mission and economy according to the RCM logical verdict. The old age-based maintenance policy was pulled down. The emphasis was put on the equipment which had effect on safety. By analysis and inspection the fault development was predicted to reduce maintenance cost and prolong maintenance period. 2. The calculation method of tube stress under carburization was derived. Combining with creep, the stress distribution of cracking furnace tube under high temperature and high carbon atmosphere was analyzed. The failure conditions were compared between creep and carburization. The tube life was obtained by Larson-Miller method under creep and carburization. The calculating results verified that the crack was supposed to occur in the out wall of tube, and the tube failure was mainly caused by carburization (creep failure generally occurred in the inner wall). 3. Critical life fraction was as failure basis. M-C method was used to calculate the tube failure probability under creep and carburization. The variety of failure probability with operation time was depicted. The results supplied the probability data with risk assessment. Compared with the failure probability by API581, the failure probability by API581 was less than the probability based on the damage model of present paper. 4. The failure consequence of tube with quantity method was calculated. The cost of injury loss, outage loss and equipment damage were obtained. The quantitative risk value was acquired 5. It was processed to defined risk levels of failure model for different components. The RCM plan based on risk for cracking furnace was formulated to reduce risk. The RCM based on risk emphasized the affect of risk compared with general RCM method. Risk based RCM focused maintenance on high risk failure model, and saved the maintenance time and cost.