Influence of the level of cathodic protection on the corrosion fatigue properties of high-strength welded joints

Effect of applied potential on fatigue crack propagation behavior of API X80 steel in seawater

“…The bare metal surface then undergoes anodic dissolution and as a result of corrosion process the crack tip surface is repassivated forming a new protective oxide film [31][32][33]35]. The pipelines and offshore structures are protected against external corrosion by means of protective coatings and CP [9][10][11]. Polarization at potentials in the range of -800 to -1,100 mV SCE is generally imposed, but very negative levels can be reached on overprotected areas close to the impressed current anodes [36,37].…”

“…X80 steels require excellent fatigue resistance in severe corrosive environment of seawater under the various loading spectrums generated by wave loading and vortex induced vibration, since the primary failure mode for such applications is corrosion fatigue [4][5][6]. To improve the service life of drilling riser, protective coating and cathodic protection (CP) are often utilized [7][8][9][10]. A great deal of guidance for CP levels for steel structure in seawater are available [9][10][11], much of which has been derived empirically.…”

“…To improve the service life of drilling riser, protective coating and cathodic protection (CP) are often utilized [7][8][9][10]. A great deal of guidance for CP levels for steel structure in seawater are available [9][10][11], much of which has been derived empirically. The CP potential required for full protection (i.e., corrosion rate reduced to insignificant level) of steel in seawater is widely considered to be around -800 mV Ag/AgCl [12].…”

“…Limited information on the near-threshold FCP behavior of high strength steels at low R ratios shows that an increase in near-threshold K (K th ) value occurs with increasing CP level [10,21,22,24]. Many studies have suggested that this is due to crack wedging effects reducing the effective stress intensity range [9,10,25,26], and the edging effect is diminished at high R ratios [10,21,22].…”

“…At present, the effectiveness of CP has not yet been proven for structural steels with yield strength above 400 MPa [9] and the guidance on the offshore installation does not define the optimum level of CP potential. It is therefore necessary to establish the optimum and safe working limits of CP for higher strength X80 steel for the riser application in marine environment.…”