Safety Assessment For Subsea Pipeline In Service

With the quick development of ocean oil gas exploitation and transportation, subsea pipeline system is playing a more and more vital role as the main means of transportation at present. Subsea pipelines are influenced by various environmental factors in the bad marine environment. Whether the pipelines can be safe in operation has been arousing people's widespread interest. Therefore, the safety assessment for subsea pipeline in service appears very important.Several aspects of pipeline safety assessment work have been researched. The details are as follows:1. Subsea pipeline reliability design method based on limit state design and the basal principle of partial safety factor methodology in DNV OS F101 code are researched. The load and resistance factor design(LRFD) method and process for submarine pipeline strength design are summarized in comparison with CCS subsea pipeline system code which is based on allowable stress design(ASD).2. The vortex induced vibration (VIV) mechanism of pipeline free span and its characteristic are analyzed. The free span natural frequency is derived for the vibration governed equation. Then the allowable free span length is derived according to different standard, and from the view of static state and dynamic state. Then these approaches are compared with each other.3. Based on the corroded pipeline burst test data, the compared study of international general methods ASME-B31G, DNV-RP-F101 and PCORRC is carrier out in the aspect of failure pressure calculation formula, safety criterion and failure standard.4. In view of the commonly used method conservation, the reference stress approach to estimate the limit load of corroded pipeline is proposed based on the reference stress definition of the full plastic structure. Nonlinear finite element analyses of pipe containing different dimensional corrosive defects are carrier out by use of the ABAQUS finite element software. The relationship between the applied pressure and the von Mises stress in the minimum ligament is found. According to this relationship, an accurate and simple new method to estimate the residual strength of corroded pipeline is proposed.