| The tubing is applied widely on oil field, and the quality of tubing thread connection effects on normal oil production. In case of Daqing Oil Field, the amount of pump checking caused by thread failure is increasing year by year, which occupies the first place among all kinds of pump checking. So it is urgent to set up an effective thread measuring method for safety at present.Aiming at the problems in the measurement of tube thread parameters, the paper presents a non-contact measuring way which makes use of the current image measuring theory and is based on linear array CCD according to API definition about thread size. The key technologies in the method are discussed in the paper. The method take the projecting photos of thread by a linear array CCD camera, the photos are inputted into computer, then the thread image can be analyzed and the size can be measured through image processing.The spiral line of taper thread can shelter the projection of teeth in axial section. The paper studies to remove the effect by regulating the position of thread axis and gives a method to judge if the thread is in right place by its image taken by linear array CCD. In order to obtain the 2-D projection data, a longitudinal traveling workbench controlled by computer is set up to realize line by line scan. One dimension thread images collected by computer are processed to filter noise and improve quality. Edge detection based on difference algorithm is introduced, which is effective to the image with step gray scale and can extracts exact edge points of thread tooth. The measuring method of 1-D thread image is discussed based on that of 2-D image. The points on tooth contour gathered by edge detection are fitted to lines, and the tooth's size can be calculate from fitted contour. The paper selects a CCD camera with small pixel and enough pixel number, which can take a projecting photo containing much more thread teeth and make it possible to measure all the main sizes only in one image, the measuring precision can also be improved at the same time.Finally, a testing program is developed with the function of data-collection , image processing and sizes calculation. The original data file, image processing and measuring result can be saved. The test shows that the system is accurate and its precision is higher than that of API gauge. Therefore, it is an effect way for tubing thread measurement. |
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