Optical inspection device for the inner surface of pipe ends

The inner surface of the holes in the ends of tubing pipes used in oil production is most prone to deterioration. The mechanical loads combined with corrosion lead to the formation of pits on the surface of the holes. A tubing burst leads to significant financial, technological and environmental losses. The existing methods of non-destructive inspection do not allow to measure the depth of a corrosion pit (cavity) on the surface of the pipe end hole. We propose the construction of the device for monitoring the pipe inner surface closely adjacent to its end. The device uses the optical principle of monitoring the presence and the depth of corrosion pits on the surface of the tubing pipe end hole. The device uses structured lighting of the ring of the hole surface. Judging by the out-of-roundness of the light-shadow border, we evaluated the depth of the defects on the hole surface. The device was tested and calibrated on a special stand, where the depth of the cavity was changed with a step of 30 microns. The reflected light flow from the target surface was recorded by a video camera. Tests of the device showed its resistance to the disturbances in the form of stray lighting, electromagnetic interference, vibrations and dirt in the room (no special operating conditions are required). The length of the corrosion pit does not affect the sensitivity of the device. If the material of the controlled tubing changes, the device shall be calibrated. For a 4 mm long defect, the depth of the corrosion pit up to 1.5 mm can be detected. Preliminary calibration of the device allows to reduce the measurement errors caused by the technological and operational reasons. The developed device is able to detect the presence of a corrosion pit on the hole surface. The accuracy of measuring the depth of the defect on the pipe surface is not less than 150 microns, which is acceptable for oil pipe repair plants. The device can be operated manually and can be built into an automated control system. The monitoring results can be documented. The developed device can be used in other areas: inspection of holes made in reinforced concrete structures, inspection of surface of the holes of chemical production pipes, GTE fuel system, etc.