Cold Work Influence on Subcritical Crack Propagation in Downhole Tubing
Cold work elevates downhole tubing dislocation density and residual tensile stress, sharply reducing K_ISSC thresholds and accelerating subcritical cracking.
13cr Martensitic
Meaning
Corrosion resistant alloys containing approximately thirteen percent chromium provide a balance of strength and durability for oilfield tubular goods. Tubing strings made of 13cr martensitic resist weight loss corrosion in environments where carbon dioxide is present. The material forms a protective oxide layer that prevents the rapid thinning of pipe walls.
Quenching and tempering are typically used to achieve the mechanical properties required for downhole service.
Alloy Composition
Iron based mixtures with chromium additions provide the necessary passive film for durability in wet gas environments. Manufacturers refine 13cr martensitic to balance carbon content with the need for corrosion resistance. High carbon levels increase hardness but can lead to chromium carbide precipitation during welding or cooling.
Low carbon variants or those with molybdenum additions offer improved resistance in slightly more aggressive fluids.
Thermal Treatment
Heat cycles determine the final strength of the metal. Producers of 13cr martensitic must carefully control the austenitizing temperature to ensure a uniform structure.
Selection Boundary
Performance depends on the presence of liquid water and the concentration of dissolved gases. Use of 13cr martensitic stops being effective when hydrogen sulfide concentrations exceed specific partial pressures. Temperature also plays a role because the protective film breaks down more easily in hot brine.
Designers select this alloy to avoid the high cost of nickel based materials while providing better life than carbon steel.