Description
Abstract: In this work, dynamic strain aging (DSA) has been reviewed to provide a comprehensive background and understanding of this failure mode, with a focus on the effect of DSA on oil and gas (O&G) production materials subjected to high temperatures such as created by fire flood operations, steam assisted gravity drainage (SAGD) wells or unintentional subsurface coal seam fires. DSA is a metallurgical phenomenon observed in a wide variety of materials, including the steels used in the oil & gas industry. DSA occurs at elevated temperatures during plastic deformation as a result of interaction between solute (i.e. interstitial) atoms and dislocations present in the microstructure. Well known manifestations of DSA are Piobert-Lüders bands or Portevin-Le Chatelier effect. It occurs over a range of material-specific combinations of temperature and strain rate, and leads to hardening, reduced ductility (brittleness), plateauing of yield stress (YS), increased ultimate tensile strength (UTS), and reduced strain rate sensitivity. From an O&G operations perspective, the strain created by intentional or unintentional thermal cycles is sufficient to cause plastic deformation of the casing (both tensile and compressive), inducing DSA. This makes a normally resistant material potentially susceptible to sulfide stress cracking (SSC) after cooling below 175oF, particularly in casing connections where the stresses are the highest. Understanding the strain hardening behavior of O&G production materials can provide insight into the structural performance during post material yielding.
Authors: Sudhakar Mahajanam and Michael Joosten
Keywords: Strain Aging, Dynamic Strain Aging, Plastic Deformation, Ductility, Elongation, Toughness, Yield Strength, Tensile Strength, Strain Rate Sensitivity, Dislocations, Solute Atoms, Interstitials, Cottrell, Snoek, Piobert-Lüders, Portevin-Lechatelier, Serrations, Slow Strain Rate Testing, Sulfide Stress Cracking, Downhole, Casing, Tubing, Steels