Study On The Corrosion And Fatigue Rule Of Sucker Rod In Plastic Lined Tubing

In recent years,a large number of Plastic lined tubing are applied in eccentric wear pumping unit in domestic oilfields,which has alleviated the problem of eccentric wear of pipe,and the sucker rod has little wear in Plastic lined tubing.But the sucker rod breaking is also the main problem in the failure accident of pumping unit well used Plastic lined tubing.Corrosion fatigue account for a large proportion through the analysis of fracture sucker rod.In this paper,the corrosion fatigue rule of sucker rod is studied in Plastic lined tubing,which provide theory basis for the fracture sucker rod in Plastic lined tubing.Wear is not the main factor of sucker rod in Plastic lined tubing.The sucker rod is in an insulated sealing environment where electrochemical corrosion occurs.Some experiment is designed to test corrosion property and fatigue property about sucker rod in Plastic lined tubing,the fatigue limit curve and corrosion fatigue limit curve are drawn based on test data.The model about corrosion fatigue rule and service life in Plastic lined tubing is established based on the theory of corrosion pit and stress concentration factor.The result show that electrochemical corrosion rate is faster than chemical corrosion,which explains that electrochemical corrosion can accelerate corrosion pit development and corrosion fatigue fracture.The test data show that fatigue limit decline from 41336 psi to 30748 psi when corrosion pit exists.The growth rule of corrosion pit and the corrosion fatigue life of sucker rod is analyzed.Some methods of improving the fatigue life are put forward such as using high chromium steel rod and covering rod.