Test Method for Corrosion Fatigue Testing of Cold Rolled Steel Wire in Sour- and Sweet Environment Based on Deflection Controlled Four Point Bending

In order to calculate the fatigue life of unbonded flexible pipes S-N curves for the armouring wires in corrosive environments are needed. No established standard method for corrosion fatigue testing exists. A test setup as well as test protocol has been developed based on deflection controlled four point bending for corrosion fatigue testing in both sour- and sweet environments.
The test setup consist of an eccentric providing an alternating sinus shape loading at loading frequencies between 0.1 to 2.0 Hz. The loading is transferred to an environmental chamber containing up to 7 specimens that are deflected in four point bending simultaneously. Each specimen is monitored with strain gauges in order to individually determine the load level. Specimen failure is detected from strain gauge signals or from externally mounted load cells. The environmental chamber system is capable of handling sour brine solutions with varying amounts of H₂S at total pressures up 10 barg.
The test protocol specifies preparation of wire samples and de-aeration and iron saturation procedures for test solution. In addition issues like pre-cycling and hydrogen charging prior to tests in sour environments are covered.