Experimental Research For Magnetic Memory Testing Technique On Stress And Stress Concentration Assessment Of Offshore Drill String

Under complex dynamic composite load condition and wicked media erosion corrosion,offshore drill string are accident prone in stress concentration sensitive area.It is of great significance to prevent the occurrence of the failure that develop the evaluation technology of drill string stress and stress concentration during tripping which can find out the abnormal state of drill and adjust the whole assembly.To this end,this paper mainly carried out the following research work:(1)Based on magnetic memory testing method,the tensile test of a typical round rod specimen of drill string is carried out.The linear relationship between tensile stress and signal in the sample in two cases is established.The empirical model of stress and magnetic signal is established to provide a basis for the stress assessment of drilling string.(2)Field test of offshore drill string was carried out by self-developed magnetic memory wellhead drill string detection device,and the evaluation methods of stress concentration by curve analysis and parameter analysis are proposed.The variation rule of drill string magnetic memory characteristic parameters with the use of the drill is obtained,and the stress concentration of the drill string is evaluated by the standard based on field data.(3)Based on the linear relationship between stress and signal amplitude,the evaluation method of drill string stress state by magnetic memory signal amplitude is proposed.According to the result of the field test,the stress distribution of drill string is evaluated.Compared with the results of mechanical calculation,the detection effect of the drill string stress distribution by magnetic memory signal are verified.And the results show that the curves of the mean of the well drill tube magnetic memory signal changes with the well depth is same with the stress of drill string.(4)The sea drill string stress concentration magnetic memory signal analysis software was adapted from actual demand.Automatic signal extraction in different areas such as drill string joint and tube is solved.The further processing of magnetic memory detection data has been realized and software support for field application is provided.