Hangbo Alloy Group
Shanghai · Est. 2012
Corrosion fatigue cracks nickel alloys under cyclic load in corrosive media. Learn the mechanism and which grades resist it in marine and sour service.
Corrosion fatigue is the combined action of a cyclic mechanical load and a corrosive environment, producing cracking at stress levels far below what the alloy would tolerate in air. Pump shafts, risers, landing-gear components, and heat-exchanger tubes fail this way because the two mechanisms accelerate each other: corrosion roughens and pits the surface to seed cracks, while cyclic stress drives them open. This guide covers the mechanism, the metallurgical factors that govern resistance, and the nickel alloys most often specified to avoid it.
Corrosion fatigue needs two things at once: a cyclic or fluctuating stress and a corrosive medium. Each cycle of loading opens microscopic slip steps at the surface; the corrosive environment attacks those freshly exposed sites faster than a passive film can reform. Pits and corrosion grooves then act as stress concentrators, and microcracks grow with every load reversal until the remaining section can no longer carry the load.
Crucially, the two processes are synergistic. Corrosion alone might be tolerable, and the cyclic stress alone might be below the dry fatigue limit, but together they drive failure at stresses a designer would consider safe. The effect is most severe in chloride or sulfide-bearing waters, especially with dissolved oxygen or acidic pH.
Two material traits matter most. First, a strong, stable passive film - high chromium (and molybdenum, for pitting resistance) keeps the surface passivated so corrosion cannot seed cracks. Second, high toughness and a fine, clean microstructure resist crack initiation and slow crack growth.
The choice depends on the environment:
Stress-corrosion cracking (SCC) needs a static tensile stress and a specific aggressive species, and can occur with no cyclic load at all. Corrosion fatigue requires a fluctuating load and is far less picky about the corrosive species - even ordinary seawater will do. The two can overlap; see our guides on chloride SCC and hydrogen embrittlement.
Inconel 625 is the most common choice for fatigue-critical marine parts because of its pitting resistance and toughness, while Monel K500 adds strength for shafts and fasteners. Both keep their properties in continuously wetted, cyclic-load service.
Reduce stress concentration at details, keep surfaces polished to remove pit-initiation sites, choose a pitting-resistant alloy for the medium, and control environment (deaeration, coatings). For subsea and sour equipment, follow our offshore subsea and sour-gas selection guides when specifying.
As a dedicated nickel alloy manufacturer serving marine, oil & gas, aerospace, power generation sectors, Hangbo Alloy Group supplies the grades discussed here across all standard product forms with full ASTM/ASME documentation and EN 10204 3.1 certification. Our material is specified for applications where corrosion resistance, high-temperature strength, and traceable quality are non-negotiable. See our production & testing facilities for more on how every heat is verified.