HXJ180 Marine Workover Machine Derrick Lightweighting Study

At present,the scale of offshore oil and gas extraction continues to rise,driving the number of workover operations to climb steadily.The workover machine is the necessary equipment for the entire well workover operation,and the derrick is used as the most critical load-bearing part of the entire well workover operation,which is subject to large loads and often causes serious accidents due to insufficient strength and stability.The HXJ180 marine workover machine is used as a kind of offshore platform well repair machine,and its derrick is mainly designed with static performance as a guideline,the small modularity and light weight requirements of the derricks were not considered,ensure the safety and reliability of the derrick only by increasing the material used for the rod,there is a huge waste of material.Suitable optimization methods are chosen to carry out lightweighting studies on derricks,which are of great engineering importance to achieve material usage reduction.This paper conducts a hydrostatic study based on different combinations of loads applied to derricks in field operations,the simulated annealing algorithm was used to carry out a size-optimization study of the derrick,the safety of the derrick was verified by performing static,dynamic and stability analysis of the lightweighted derrick.(1)Based on finite element analysis theory,API 4F 2020 and AISC 360-16 American Code for Structural Steel Buildings,the truss 3D model of the HXJ180 offshore workover derrick was created using APDL command flow,the constant load,working load and wind load to which the derrick is subjected during operation are calculated,the derricks are divided into three types of conditions,namely windless conditions,operational conditions and preservation of equipment,according to the different combinations of loads to which they are subjected in actual operation,the effect of wind loading direction is taken into account,and a static analysis of the derrick is carried out and extreme working conditions are obtained,the results show that the static properties of the derrick satisfy the stiffness and strength design criteria.(2)Based on the results of the static analysis,the mathematical model of derrick size optimization design is established according to AISC 360-16 American Code for Structural Steel Buildings,which specifies the derrick rod section size below 50 MPa as the design variable for size optimization,the stiffness and strength criteria as the constraints for optimization,reducing the overall weight of the derrick is used as an objective function for optimization,the mathematical model for derrick size optimization is developed,the overall weight of the derrick was reduced by 8.6% using the simulated annealing algorithm,and the static properties of the derrick met the stiffness and strength criteria after the lightweighting.(3)Based on the structure of the lightened derrick,modal analysis,harmonic response analysis,wave spectrum analysis and transient dynamics analysis are carried out.The first eighth-order intrinsic frequency of the derrick is 2.0299～10.726 Hz,and large deformation occurs in X-direction,simple harmonic load action derrick in 2.5HZ,8.1HZ when the peak excitation frequency,X-direction produce large deformation,wave loads acting on the offshore platform can cause large displacement of the derrick in the Z-direction,The combined effect of impact load and operational wind load produces large deformation of the derrick in the X-direction,which is significantly higher compared to the static load.The results of the above dynamics study show that the dynamics of the derrick after lightweighting meet the requirements of the design guidelines.(4)Based on the static dynamic characteristics of the lightweighted derrick,the local and overall stability of the derrick is studied,and the buckling analysis of the lightweighted derrick is carried out using finite element software.In the extreme working conditions of the lightweight derrick,both the local rod and the whole will not be destabilized,while the hook load has more influence on the overall stability of the derrick than the wind load.The results show that the stability of the lightweight derrick meets the working safety requirementsThe lightweight study of HXJ180 marine workover machine derrick was carried out,and the obtained lightweight derrick structure was proved to meet the requirements of work safety in both static dynamic performance and stability,which can provide systematic and scientific theoretical support for the design and manufacture of offshore derricks and lightweight study.