Abstract
This paper presents a corrosion fatigue cyclic failure test for X80 steel, which has arc sprayed with an Al–Zn coating in natural seawater under different stress levels. We found that the Al–Zn coating can significantly improve the corrosion fatigue resistance and slow the crack initiation of X80 steel. The effect of the Al–Zn coating on the corrosion fatigue crack initiation is mainly attributed to its physical isolation, cathodic protection and residual prestress while the effect on crack propagation is due to its inhibition of the formation and evolution of secondary cracks. Moreover, according to the test results, a new life prediction model for corrosion fatigue based on the damage evolution law is proposed and the effect of corrosion–fatigue coupling damage in the proposed model is also considered.
Highlights
As a piece of key equipment for deep-sea oil exploration, the safety and reliability of drilling risers have attracted an increasing amount of attention [1]
It can be noted that the corrosion fatigue life of the coated X80 steel is longer than that without coating and it decreases as the stress amplitude increases
+ T0 f dt dt dt dt where D, Dc, Dscc and Df are the corrosion fatigue damage, corrosion damage, stress corrosion damage induced by average stress, and fatigue damage caused by stress amplitude, respectively, t is time, N is the number of cycles, and T0 is the period of fatigue loading
Summary
As a piece of key equipment for deep-sea oil exploration, the safety and reliability of drilling risers have attracted an increasing amount of attention [1]. The riser always undergoes large reciprocating deformation under the actions of the currents and waves in addition to suffering from the corrosion effect of seawater. The failure period of corrosion fatigue is generally divided into three stages: Crack nucleation, fatigue crack propagation, and rupture. The first two stages determine the service life [5,6]. Corrosion fatigue failure preferentially initiates from corrosion pits [7,8] due to the anodic dissolution inside the pits accelerated by mechanochemical effects [7] and irreparable damage caused by corrosion products [8]. The mechanism of fatigue crack propagation is very complicated and it is difficult to generalize this mechanism, the effect of corrosion on crack propagation is definitely not negligible [9,10,11]. The methods for inhibiting corrosion to extend the corrosion fatigue life has been widely adopted, such as surface enhancement by laser [12], low plasticity burnishing [13]
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