Environmental cracking of high strength casing in mud has been experienced but its mechanism has not been cladied. Degradation of lignate mud with time and its effects on steel in the mud were experimentally investigated in a laboratory. Sulflde concentration of mud increases and pH value of mud decreases with aging time. In an
aged mud, hydrogen absorption and cracking of steel were observed when pH of the mud was lowered. Sulfde which was formed from mud change into H2S by a decrease in pH which was caused by dissolution of CO2. CO2 was observed to form from mud. As the result, sulfide stress cracking occurs, which is a proposed mechanism of cracking of casing in mud.
Keywords: High Strength Steel, High Strength Casing, Mud, Hydrogen Embrittlement, Environmental Cracking, Suliide Stress Cracking