Very often the current body of knowledge and literature of fatigue performance in coke drums and blowdown piping system are linked to fatigue testing performed in air or in water. This paper summarizes the test results that were conducted using process fluids collected from a delayed coker. Both fatigue crack growth rate (FCGR) tests and stress/strain – cycle fatigue endurance tests in sour water at 200°F (93°C) or in a hot oil mix at 460°F (238°C), with gas mixture containing H2S were conducted. Carbon steel, Alloy 625 and their corresponding weld metal specimens were tested. The test results indicate remarkable impact of environment on fatigue behavior. Frequency scanning FCGR tests in sour water environment showed that FCGR increased with decreasing load frequency, particularly with high ?K (32 ksi·vin or 35 MPa·vm ). When ?K was between 12 ksi·vin (13MPa·vm) and 36 ksi·vin (40 MPa·vm), FCGR of all specimens in sour water are higher than the mean + 2 SD (Standard Deviation) curve of carbon steel in air. Fatigue endurance tests in both sour water and hot oil environments showed various ranges of knock-down factors compared to test results in air. This testing program provides a better definition of the corrosion fatigue cracking mechanism of materials in delayed coker process. It also helps in the inspection planning of delayed coker equipment and in decisions on material selection.