Study On Safety Comprehensive Evaluation Methods Of In-service Rig Derrick

Derrick is an important part of oil rig, its safety performance is directly related to the operation of a complete set of rig system. As a kind of complex carrying space steel structure, derrick is ofen affected by many factors during using, for example, dismounting and mounting, transportation, overload and corrosion, etc. and the carried load is random. So the potential risk of injuries and destruction is very big, the safety of structures is threatened. More seriously, if some important parts have been damaged, its destruction degree will develop rapidly, quickly lead to the destruction of the whole structure and cause catastrophic tragedy. In order to ensure life and property security, reduce the great economic losses and repair in-service rig derrick reasonably and reduce maintenance costs, it is particularly necessary and urgent to take effective technical means and methods for the testing, health diagnosis and safety evaluation of in-service rig derrick. Therefore, it has very important theoretical significance and practical significance that study on the damage diagnosis and performance evaluation method is carried out to establish the safety evaluation system of derrick.This paper studies the key scientific and technological problems about safety evaluation of in-service rig derrick. The main research contents and results are as follows:(1) The numerical analysis method of in-service rig derrick with damage was studied. Using analysis platform based on finite element method, the numerical model analysis method that can describe the implicit relationship between damage factors and performance parameters of in-service rig derrick is put forward. Through analyzing damage and its mechanism, damage mathematical fomulas is established, the damage functions are introduced, the influence of damage on structure characteristics is revealed, consequent damage numerical models of in-service rig derrick are established, thereby the method of damage numerical simulation is proposed. The analysis offers foundation for further model updating and performance evaluation.(2) The testing theory and method for performance evaluation of rig derrick is studied. According to the features and characters of rig derrick, the static and dynamic testing methods are explained. Firstly, aiming at the shortcomings of the traditional strain test, the wireless stress testing technology and system is developed, that can be used for safety testing of rig derrick. The principle of wireless stress test is theoretically analyzed. The efficiency and reliability of WiFi wireless test system is proved by the comparison test. It can provide good foundation data for further performance evaluation; Secondly, some testing parameters during modal test are discussed in detail, such as motivational pattern, sensor location and frequency resolution etc. A novel method about experimental modal parameters identification under ambient random excitation is deduced. Based on these, the problems and its solutions on the incomplete measuerments are discussed.(3) The model updating method based on parameter inversion of rig derrick is studied. Firstly, the paper expounds the basic ideas and framework of parameter inversion. And then the inversion model updating method based on optimization is proposed, comprehensivly considering the static and modal parameters. A sensitivity analysis method suitable for practical engineering applications is deduced according to its physical meaning, then sensitivity parameters are accqured. The optimal updating function was established according to residual equation between test and theory parameters. Combined with first-order optimization algorithm and genetic algorithm, the improved objective function is proposed to solve this problem. Inversion calculation efficiency is obviously improved, and the computation precision is reliable. The inversion method has been verified by experimental analysis of derrick model. The solutions on model updating problem the in-service rig derrick suitable to engineering application are given, that is:multi-stage inversion model updating method, partial inversion model method combined with the direct updating and the static and dynamic hierarchical model updating method.(4) From the point of view of the using safety, this paper systematically analyzes the comprehensive evaluation method of in-service rig derrick based on the empirical judgment and parameters inversion. Three typical engineering examples have been done the performance evaluation, and the result verified the availability of three kinds of updating methods, that is:the model updating method based on the static parameters, the model updating method based on the modal parameters and stratified updating method combined with static and dynamic index. It provides a new idea for the performance evaluation and the condition assessment of in-service rig derrick. API standard as the main line, considering comprehensively the particular situation of the ultimate load, hoisting condition and wind load, etc, the using safety of one typical engineering example is analysed so as to realize the comprehensive performance evaluation. It can provide the security for the operating safty of in-service rig derrick.