Non-Destructive Testing

Non-destructive testing of downhole equipment is a way to determine its characteristics without violating the integrity, serviceability and reliability of the structure of the equipment under study. SCL utilizes the following non-destructive testing:

  • Optical-laser inspection of screen slot clearances. 
  • Equipment welds defectoscopy. 
  • Ultrasonic thickness gauging. 

Optical-laser control of screen slot gaps

Two basic methods are used to check the winding quality of slot screens of sand screens: manual with metric probes and automatic with an optical inspection machine. The manual method is quite time consuming and imprecise. The SCL laboratory uses the Kvantron-150 laser-optical complex to check screen slot gaps. The principle of the inspection machine is to obtain a digital black-and-white image of the screen slot clearances of high accuracy with highlighting of the light and shadow borders that define the boundaries of the screen slot clearances. Automatic inspection with an inspection machine allows the distribution of slot gaps along the entire length of the screen element to be checked with a high accuracy of 10 microns. The distribution of screen slot gaps has a significant impact on the effects of sanding and colmatation, so controlling the slots is important. 

There are several criteria different screen manufacturers and customers use to evaluate the slot gaps distribution. The inspection machine software system is set up to evaluate the clearance distribution according to Statoil, Schlumberger, Exxon criteria.  All the evaluation criteria are set up along roughly the same principles. At least a certain fraction of the clearances must fall within a given interval around the nominal with a given probability. The choice of the clearance distribution evaluation criterion is determined in accordance with the Customer’s requirements. The Automatic Slotted Gaps Test program involves testing a sample screen along the entire length of the screen element with rotation around the axis. 

Оптический контроль щелевых зазоров
Оптический контроль щелевых зазоров

Kvantron-150 optical-laser screen gaps inspection machine

Technical characteristics of the inspection machine:

  • Length of unloading table for horizontal movement of the scanner -10000 mm
  • Screen size – 3 ½ – 7 "
  • Screen slot clearances – 100 – 1000 microns
  • Units of the movement system: horizontal movement unit, vertical movement unit, unit of screen rotation around the axis
  • Micrometer resolution – 5 microns
  • Calibration accuracy – 10 microns
  • Scanning speed – 3-5 slots/sec. 
  • Auxiliary subsystems of the stand:
    • Control unit with touch screen
    • Industrial lighting 
    • Laser range finder

Work scheme:

  • The sample to be tested is placed on the table of the inspection machine. The test program is selected with the criterion by which the slot clearance distribution will be evaluated. 
  • Starts the test process with the option to stop when the clearance deviates by a certain amount. The column with the scanner of the inspection machine automatically moves to the starting position for testing the screen element. 
  • The inspection machine enters the scanning mode with the help of the remote distance adjustment subsystem to scan the screen element. In this mode, the scanning speed reaches a value of 3-5 clearances per second. The vertical scanner movement system allows you to adjust the distance of the scanner to the screen surface to ensure that the image is in focus. 
  • If the inspection machine registers an abnormal slot clearance whose size differs from the nominal by more than the specified parameter, the scanning is stopped. The operator re-checks the abnormal slot situation with the probe. 
  • After each test, the inspection machine generates a report on the slot-clearance distribution with a calculation of the statistical parameters of this distribution and an evaluation of the fulfillment of validity criterion of this distribution. 
  • After the entire test series, a general test report is made indicating the fulfillment of the validity criterion of the wire winding. 

The inspection machine is periodically calibrated as a measuring instrument. The measurement accuracy of the inspection machine is confirmed by certification in independent metrology laboratories. 

Welds defectoscopy

To control the quality of welded joints of downhole equipment, the laboratory uses the method of capillary defectoscopy of welded joints. The method is based on the penetration of liquid substances through the weld seam by capillary forces. When using the capillary flaw detection method, the color contrast of the defective area of the weld is increased compared to the quality weld. Various defects related to the non-welded seam line, pores and sinks can be detected using this method of capillary flaw detection.

For this test, a specially colored indicator is used, which is capable of filling open cavities, with the subsequent formation of an indicator pattern. Surface-active substances (surfactants) are added to this indicator in order to improve the penetration of the indicator liquid into the existing cavities of the weld. Using a special developer, the indicator material is fixed to fully reveal defects in welds.

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