Research On Risk Assessment Method And Preventive Maintenance Strategy Of Cranes

Crane is one of the mechanical and electrical kind of special equipments that have most hidden danger factors, highest accident consequences and most serious accidents. At present, the number of crane grew by an average of about 20%, and the total number of all kinds of cranes is more than 2.5 million. At the same time, the proportion of crane casualty accidents in all kinds of casualty accidents also increased year by year. At present, the casualty accidents in lifting operation of the various regions and industries in our country accounted for about 25% of all deaths and injuries. Therefore, strengthening crane safety management and accident prevention is urgently needed. Risk assessment is the premise and basis of accident prevention. At present, systematic risk assessment method for cranes is limited. For the currently used hoisting equipments, especially the overage ones, the research on systematic and practical risk assessment method has great theoretical significance and practical value in engineering.At present, the industry adopted means of legal and periodical inspection to realize the safety operation and accident prevention of cranes. This system has the fundamental protection function for the safe operation of the hoisting equipments to a certain extent. However, because the inspection items and the inspection period is basically fixed, not to distinguish different enterprises and individual equipment is likely to cause excessive inspection of general equipment and insufficient inspection on high-risk equipment; There are only qualitative inspection results as "qualified" and "unqualified", the results of safey situation assessment has limited reference value for crane accident prevention because there isn't quantitative calculation for the risk of crane's component. In the paper, research work about the risk assessment method and the preventive maintenance strategy of crane and related problems is conducted. Such work is completed as FMEA analysis of cranes, the information collection of failure data, and the general failure probability, the reliability experiment of small wire rope samples, the virtual modeling and calculation of cranes, the qualitative and quantitative evaluation calculation of the component's risk, the establishment of RCM preventive maintenance strategy of cranes, the safety assessment implementation specifications of cranes and the establishment of the assessment software, etc. The specific research content of the paper is as follows:(1) The database of crane failure mode is established on the basis of completing the field research of faults of more than 380 cranes. The failure mode and effect analysis is conducted, and all of its failure modes are obtained, and then the corresponding failure causes and failure consequences are analyzed. To the typical failure modes of wire rope bending fatigue and wear, the small sample physical experiment is carried out to obtain the failure data in the field test condition. The failure samples acquisition table of crane parts is designed. The large sample failure data of some crane parts are obtained by using the questionnaire and in-depth field research methods in the manufacturers and users of cranes such as LingGang Co., Ltd., AnGang Co., Ltd. and Sanyo heavy industry Co., Ltd. The corresponding failure life calculation, then, is completed.(2) In view of the fact that crane parts usually only have small sample field failure data, the reliability life prediction method for small samples of crane parts is proposed on the basis of the Bayesian theory. A priori distribution of the reliability evaluation is determined on the basis of the experiment data of parts in the development phase and relevant or similar inspection records of like parts. With the combination of the field reliability test data of the small samples and application of the Bayesian method in combination with the priori information of the product and the field test data, the posteriori distribution of the reliability life of the product is obtained. The life prediction of the product is then achieved. Under the condition of lack of field failure data, the method provides a new way for obtaining failure life of the crane parts.(3) The virtual simulation experiment platform of crane is established by using the secondary development function of finite element analysis software. The parameterized virtual modeling and working loading of the tower crane is implemented. And then, the analysis results of the structure strength, stiffness and stability of integral crane is automatically obtained by use of Ansys software so as to provide the reference for the structure safety assessment of cranes.(4) On the basis of finishing FMEA analysis and obtaining the information of general failure probability of the main parts, the qualitative risk assessment model of crane is established by use of RBI technology, and the high risky parts of crane are determined. The modified calculation model of the failure probability of the crane parts is established on the basis of analytic hierarchy process (AHP) and grey comprehensive evaluation technology. Finally, the practical assessment method is proposed, that is the parts whose assessment result sequencing is highly risky in the qualitative risk assessment will carry out further quantitative assessment by use of the above method.(5) The safety assessment system software of crane is established on the basis of ACCESS database and with VB software as the developing tools. The software can automatically complete qualitative and quantitative risk assessment of the crane parts, output WORD format assessment report and give suggestion about the corresponding inspection areas, inspection methods and inspection period.(6) The research on preventive maintenance strategy of cranes is carried out on the basis of RCM technology. A calculation method about incomplete preventive maintenance period in limited life time is provided with the comprehensive consideration of reliability, economy and availability of the parts in the maintenance interval period. For those parts with measurable potential degradation process, with the consideration of the failure process, the non-periodical situational maintenance strategy on the basis of first time inspection and duplicated inspection is proposed. A method for calculating the optimum inspection period is presented on the basis of economical efficiency and availability criteria.(7) Theoretical research results are integrated and the risk assessment implementation regulation of cranes is made. The practical quantitative assessment criteria of each factor rating in analytic hierarchy process (AHP) are presented. The standard implementation of processes and specifications for qualitative and quantitative risk assessment of the crane parts is formulated. Finally, nearly 20 cases of crane risk assessment engineering application are completed on the basis of the implementation regulation and assessment software.