Load-Carrying Capacity Analysis on Derrick of Offshore Module Drilling Rig

Abstract

Offshore module drilling rig has become an important equipment of offshore oil and gas development, espe- cially, the significantly future application in the field of deep water. Due to the long time working and complex working conditions of in-service derrick of offshore module drilling rig, analysis of its load-carrying capacity assessment is of great significance. Field test shows that in common the derrick of offshore module drilling has an intrinsic defect of stress concentration in addition to external damages including initial bending and load eccentricity. In this paper, the finite ele- ment method is combined with field test method, two assessment methods are put forward, respectively. Stress concentra- tion detection on derrick main rod is carried out by using metal magnetic memory detector, and the detection results show that larger degree of stress concentration phenomenon exists on eleven rods of derrick, and stress concentration degree of individual rod is serious. Loading stress test and finite element analysis are carried out on the derrick of offshore module drilling rig. According to comprehensive comparison, it is concluded that hoisting capacity for the derrick cannot reach 4500 kN. Two kinds of structure reinforcement scheme are proposed, and comparison results show that the reinforcement scheme with four legs can improve the actual load-carrying capacity of the derrick. Reinforced derrick can achieve the new design value of derrick carrying capacity. In this study, the evaluation method is correct, which can analyze the der- rick carrying capacity of offshore module drilling rig more objective and accurate, and we also provide a new train of thought and reference for the steel structure carrying capacity assessment.