Reliability And Risk Assessment For Structures And Equipment Of Offshore Platforms

Offshore platforms play an important role in the oil and gas exploitation process in offshore areas. The collapse of offshore platforms under extreme environment and fire/explosion accidents in the upper platform module will all lead to life losses, economic losses and environmental pollution, therefore, they all need to be studied thoroughly. The collapse of offshore platforms under extreme environment is normally caused by the lack of ultimate strength, and the ultimate strength assessment for the platforms based on reliability method plays an important role in this area. However, it is still difficult in reliability method to consider the problem that the ultimate strength will decrease with time. Fire and explosion accidents caused by gas leak takes a great proportion in the accidents of upper platform module, and risk assessment method is generally used for these accidents. However, most of the methods are based on qualitative assessment and rely on engineering experience greatly. This article conducts deep research on these problems and the main contents are list as below:(1) A time-dependent reliability method, which is thought suitable for the ultimate strength of offshore jacket platforms, is proposed here, and the corrosion effect on the ultimate strength decrease is taken into consideration. The environment loads of extreme storm and extreme ice are both studied respectively in an example platform.(2) With the fire/explosion risks caused by the gas leak in the upper platform module taken into consideration, a quantitative risk assessment method is proposed here. This method has merged the discrete region analysis technology, frequency/probability analysis technology and CFD analysis technology. Based on the method proposed here, a certain number of leak scenarios can be generated, and the subsequent fire scenarios and explosion scenarios can be assured. The probability of every scenario can also be calculated properly. The accidental design load method based on cumulative probability curve is given then.(3) The Fire Dynamic Simulation (FDS) software which is based on CFD theory is taken to model the jet fire. Comparing with an experiment is conducted to validate the method used. A typical upper platform module under jet fire is modeled by FDS to study the temperature and velocity distribution characteristics, and different jet fire scenarios are undertaken to study their effect on temperature and velocity fields.(4) ABAQUS software is taken to simulate the structural analysis under high temperature. An experiment of a simply supported beam under high temperature is used to validate the analysis method used here. Simulation method based on FDS and ABAQUS for upper platform module under jet fire scenarios is studied and the failure mechanism of the module is discussed in detail.(5) FLACS software, whicn is also based on CFD theory, is taken to study the gas explosion simulation method. A gas explosion experiment is taken to validate the method used in this article. The simulation method for gas explosion on the upper platform module is also studied here, and the explosion propagation characteristics and the overpressure distribution characteristics are discussed in detail. The effects of blocking and lateral restriction on the overpressure distribution are also studied thoroughly.(6) Simulation method based on LS-DYNA for structural response under explosion load is studied. A blast wall experiment is taken to validate the method. The effects of the triangle load types on the structural response based on LS-DYNA and theoretical anlysis are conducted. Simulation method based on FLACS and LS-DYNA for the dynamic response of upper platform modules under gas explosion is studied, and the failure mechanism of the module is discussed in detail.(7) Different risk decreasing principles for fire/explosion risks are studied. The suitability for applying the RCM method on the maintenance of leak equipment to reduce fire/explosion risks is studied. A proper inspection interval model is proposed for the on-condition task of RCM.