Study On The Optimal Design Of Joint Thread Of Core Drill Tool

The core drilling tool is used for drilling to obtain the soil or core below the surface,and is widely used in oil and gas resources exploration and development,engineering survey,and environmental monitoring sampling.The core drilling tool is complex in structure and expensive in the whole drill string.the thread part is alternately superimposed by various internal and external pressures,axial loads,torques,bending moments and the like.The action is prone to breakage and deformation,resulting in failure of the connection,and the entire core drilling tool cannot be used any more.It is necessary to drill and replace the pipe fittings,causing a large economic loss.The core drilling tool needs to bear the task of carrying and wrapping the core or provide the channel for coring,so the wall thickness is much smaller than that of the ordinary drill pipe,and the threaded portion of the connection is correspondingly thinner.However,it bears the same load.If the conventional drill pipe thread is still used here,it will bear the risk of dangerous accidents at any time.Therefore,it is necessary to separately study the thread of the core drilling tool.In this paper,ANSYS is used to analyze the stress distribution at the joint thread under different loads.The results show that the thread of the drill pipe joint has a high intermediate and low stress distribution at both ends under the load,and the joint thread outer ring near the load application end.The stress value is the highest,which is due to the deformation of the end to absorb energy,so that the middle part of the threaded joint is not easy to be deformed;the outer ring thread stress value far from the load application end is increased,and the increase is larger as the load increases,which is made of thread The helicoidal surface is caused by the increase in load and the interference.According to this rule,an optimization scheme for reducing the height of the thread of the first 3 turns of the joint is proposed.The results show that the scheme reduces the stress concentration factor on the joint thread by 14%.The analysis shows that the smaller the taper of the thread,the smaller the stress concentration factor on the thread;the stress concentration of the 15° thread The coefficient is the smallest.Through experimental verification,the experimental results are consistent with the simulation results.The 15° angled thread has the highest axial load carrying capacity,but the thread tightness is lower than the 30° thread.Increasing the thread height to 2.44 mm is beneficial.Improve the axial load carrying capacity of the thread,but the effect is lower than the 15° thread,and the overall air tightness of the thread is also reduced.This paper combine the simulation and experiment of the thin-wall coring tool joint thread and provides a reference for the design of various requirements of the drill pipe joint thread in the future,and strengthens the strength of the core thread of the coring tool and increases the drilling speed.