High-pressure manifolds are subjected to repeated pressure cycles, vibration, thermal changes, and installation loads. Fatigue crack growth can occur at weld toes, thread roots, branch intersections, transition radii, seal grooves, and other stress-concentration areas.
Life analysis begins with pressure-cycle history, material properties, geometry, initial flaw size, and inspection sensitivity. Finite element stress analysis and fracture mechanics can be used to estimate crack growth under the expected operating spectrum.
Material toughness, heat treatment, residual stress, surface finish, and corrosion environment all affect crack-growth behavior. Sour service and corrosive fluids require additional attention to sulfide stress cracking and corrosion fatigue.
Practical life management includes pressure rating control, proper support of flowlines, avoidance of excessive hammer impact, regular visual inspection, magnetic-particle or ultrasonic testing, and replacement of components that exceed the defined service limit.
