Environment induced fatigue crack of type 40Cr steel in drilling muds

Drill pipes are subjected in service to aggressive environment (a wide rang e of drilling muds) and to a combination of high static and dynamic loads. Under such conditions, the high-strength steel is susceptible to various fo rms of environmental cracking, particularly to corrosion fatigue. The fatig ue life of type 40Cr steel in salt drilling muds was studied with a self-ma de rotating bending corrosion fatigue testing apparatus. Environmental vari ables investigated included stress, frequency, temperature, and pressure of carbon dioxide. Experimental results show that carbon dioxide promotes the fatigue crack of 40Cr steel. These tests were supported by electrochemical corrosion measurements and hydrogen permeation.