Study On The Tubing Thread Measuring Method Based On Digital Image Processing

Tubing is widely used in oil exploration. The quality of tubing thread has direct effect on the oil production. Due to the uneven quality of tubing, many oil fields are suffering the thread gluing, leak, slipping and collapse, even fracture of tubing, which make great loss on economy and labor in the oil production.In the process of tubing's production and repair, the use of unqualified tubing can be effectively reduced by detecting, analyzing and evaluating the quality of tubing thread. This is helpful to the stability and high production of oil exploration. However, because of the underdeveloped technology, the detection and evaluation on tubing threads are still based on manual work in our country. This may cause more detecting error and lower efficiency. What's more, the detecting result is directly affected by people's experience and other human factors, lacking of strict standard.According to the requirement of tubing thread measurement, this paper works out a tubing thread measuring method based on digital image processing, which has high reliability, precise detection, high speed, high integration and intelligence. Firstly, it analyzes the digital image processing technology synthetically, comparing the algorithms on image prior-processing, image binaryzation, edge detection and subpixel location. It uses the median filtering to prior-process the tubing thread image, and then cuts up the image with the histogram method in the step of image binaryzation. It detects the tubing thread edge by the improved Canny operator and locates the subpixel edge of the image based on the polynomial interpolation method to increase the precision. Finally, according to the appearance characteristics of tubing threads and the philosophy of measurement defined by API, in term of the basic size of the tubing thread made in our country, the image is measured in order to get the values of tapers, inclined angles, thread pitches, heights and pitch diameters. The surface appearance of the tubing thread is also detected.The experiment makes use of the system with a digital camera and the self-made lighting source to test the measurement method. Experiments have showed that the measurement is accurate and can entirely satisfy the requirements of measuring tubing threads. It is an effective method to measure the tubing outside thread.