Impact Analysis Of Corrosion On The Strength And Reliability Of Jacket Offshore Platform

Jacket offshore platform is a structure form which is widely used in offshore oil development at present. The steel frame of the platform is eroded by the ocean atmosphere, seawater and sea creatures, for which it is in salt fog, humidity, seawater and other harsh marine environment for a long time. As a result, it can be seen severe corrosion which also has a great diversity of types on the platform.Various types of corrosion changes the mechanical properties of the jacket offshore platform structure material, reduces platform strength and ultimate bearing capacity, affects the service life and safety of the platform and results in offshore platform accidents. Therefore, to insure the security and usability of platform structure, it is quite essential to make a scientific study on the impact of corrosion on the strength and reliability of offshore jacket offshore platform.Through the method of reviewing the literature, theoretical analysis and finite element analysis by ANSYS software, with the CB812 oil well group platform as the research object, following works have been done in this paper: First of all, the corrosion forms of offshore jacket platform under marine environment are fully described, including general corrosion and partial corrosion. Next, a finite element model of platform under no corrosion damage conditions is established, and the stress distribution is obtained by static analysis, at the same time, the ultimate bearing capacity of the platform is obtained by stepwise loading. Then, considering the uniform corrosion and local corrosion respectively, this paper sets up the overall finite element and local entity model of the platform under corrosion damage,and makes stress analysis of them and gets the influence of two kinds of corrosion on the strength of the jacket offshore platform by comparing the results with the tress of no corrosion damage. Finally, the failure probability and reliability index of the platform are calculated respectively in the conditions of initial no corrosion damage and uniform corrosion damage in the service period. In addition, the influence of corrosion on the platform reliability is obtained by comparison and analysis. The conclusions are as follows: Firstly, serious corrosion will develop on the jacket offshore platform in the marine environment, including general corrosion and local corrosion, both of them will lead to stress concentration, the stress concentration of the local corrosion is more serious and the influence on the strength of the platform is larger. Secondly, when the pit group is generating, the pits will affect each other in a certain range. Thirdly, the stress concentration is more serious and the maximum stress is greater when the local pit corrosion is distributed along the circular direction of the pipe wall rather than along the axial direction. Fourthly, the failure probability of the offshore jacket platform with uniform corrosion damage is increasing year by year during the service period, and reliability index is reduced. That is to say, corrosion will reduce the reliability of the platform.