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Downhole corrosion behavior of Ni-W coated carbon steel tubing was studied in spent acid (dilute HCl)solution by using autoclave and electrochemical techniques,in which dilute HCl with pH ranged from 1 to 4 is used to simulate the spent acid during flowback in fracture acidizing process before production.The weight loss and electrochemical results indicated that Ni-W coating has lower corrosion rate than uncoated carbon steel in spent acid and formation water.According to weight loss test in autoclave in terms of simulating downhole environment, corrosion rate ratio of carbon steel to Ni-W coated carbon steel is 13.7,14.5, and 6.9 in spent acid with pH =1, pH =2, and pH =4, respectively.Moreover, the sealing performance of full-scale Ni-W coated carbon steel tubing was evaluated by using make-and-break test, hydraulic bursting test, and extreme downhole condition corrosion test.No thread galling was found after 4 times of make up and three times of break out by using maximum recommended makeup torque of 4258 lbf-ft, no leakage was detected after hydraulic bursting test at 95.0 MPa for 30 mins, and it is observed very slight corrosion on the tubing shoulder after experiencing make-and-break test under extreme downhole condition.