Analysis of Fatigue and Corrosion in Subsea Pipelines

This work evaluates the resistance of oil prospecting pipes to fatigue stresses generated by vortex-induced vibrations (VIV's) on the high seas, associated with wear caused by corrosion, a phenomenon that is aggravated in this environment. The study was based on the Stress x Number of Cycles curve of specimens with and without corrosion, taken from an API 5CT T95 pipe (1% Cr). The fatigue tests were carried out in the laboratory and the forced corrosion took place in a salt-spray chamber. To complement the results obtained in the fatigue test, microhardness, surface roughness, mass loss assessment, scanning electron microscopy and optical microscopy were also carried out. The corroded specimens showed an increase in roughness and a reduction in fatigue life compared to the uncorroded specimens, especially at higher stresses. The microhardness and microscopy tests showed anisotropy between the transverse and longitudinal directions of the tube. VIV's generate stresses of up to 250 MPa and the tests showed that for stresses below 350 MPa there should be no fatigue failure, which indicates that the pipe in question is suitable for offshore applications.

Autorentext

Abschluss: MATERIALS ENGINEERING - UNESP Betreutes Forschungsprojekt - Mechanische und mikrostrukturelle Charakterisierung eines API x65 Stahls. Stipendium des Pro-Rektorats für Erweiterung/PROPE UNESP - Ermüdungs- und Korrosionsverhalten eines widerstandsgeschweißten API 5CT T95 Stahlrohrs. Schweißaufsichtsbeamter der Stufe 1 - FBTS/UFRJ.