Characteristics And Propagation Attenuation Property Of Acoustic Emission Signals Of Freezing Pipe Fracture

The freezing pipe is the key to the formation and maintenance of the frozen wall in the freeze sinking,and the fracture will cause the saltwater leakage,the freezing wall to melt,and even flooded well accident.Freezing pipe fracture accident often occurs abruptly and easily causes a chain reaction,which is a serious threat to drilling safety.Therefore,in the current situation of freezing pipe fracture accident occurring from time to time and not being detected in time,the method of indoor test,physical model test and numerical simulation is used to study on acoustic emission signal characteristics and its propagation attenuation property at the moment of freezing pipe fracture.It will lay a theoretical foundation for research and application of acoustic emission technology in the freezing pipe fracture detection.First of all,In view of the special working conditions of the freezing pipe,the indoor test method of the freezing pipe fracture acoustic emission was carried out.Through the indoor experiment,the formula of various frozen soil similar materials with the main change index of elastic modulus was obtained.Based on the prototype of "freezing pipe(including lining pipe joint)constrained tightly by the artificially frozen soil ",the simplified and optimized size of the freezing pipe specimen was studied by means of model test.Consequently,the specimen model of the acoustic emission test is determined.In order to ensure that the model test can effectively simulate the acoustic emission characteristics of the freezing pipe in the actual working conditions,the validity of the acoustic emission similarity criterion is verified by experiments.Based on the model test,the denoising and characteristics of the freezing pipe fracture signal obtained by the experiment are extracted.Then,under the condition of various affected factors,such as freezing pipe geometry size,frozen soil elastic modulus,loading method,experiments under the pure tensile and bending and tensile fracture type were conducted on acoustic emission of freezing pipe fracture to find out how these factors affect feature parameters of acoustic emission signals,such as frequency range,amplitude changes.And then,based on the experiment results,such as frequency range,main frequency,by means of numerical simulation,the specific frequency sound waves were excited instead of the same frequency components to study the influence of complex factors such as soil change,frozen soil modulus and number of pipe joints on the propagation attenuation characteristics and attenuation coefficient of the acoustic wave along the freezing pipe.In conclusion,through a comprehensive analysis and comparison of experimental results,the extreme detectable distance and its discrimination criterions of acoustic emission signals of freezing pipe fracture was obtained.