Analysis on Tripping Reasons of a Repaired Tube in One Well

Thread tripping happened to the forty-third oil tube in one well of Tarim Oilfield during playing out perforated completion integrated pipe string. The tripping tube was a ø73.02 mm×5.51 mm repaired tube, which was degraded to N80 steel. The tripping tube and several unused tubes of the same repairing batch were sampled and tested physically and chemically to analyze the tripping reasons. The results show that:the material and mechanical properties of the repaired tube all met the requirements of standards; unqualified thread parameter and galling phenomenon happened to the repaired tubes of the same batch, however the tensile failure load of the repaired tubes met the requirements of API TR 5C3-2008 that the failure load should be no less than 471.5 kN, so the unqualified thread parameter was not the main reason for the tripping of the oil tube. The macro morphology of the oil tube and stress situation of the tubing string during tripping were further analyzed, it was considered that the main reason of the thread tripping was thread alternating during making-up, which made the tube galling and incompletely making up. The joint strength of the joint was greatly reduced, and a low load slip failure happened at last.