Fretting Fatigue Design of Subsea Connectors: Matching Results Between Pairs of Tests

Abstract The upper end of a subsea wellhead system has an external wellhead hub profile. The standardised H4 profile is widely used. A wellhead connector is latched on the wellhead profile by use of locking devices with a matching internal profile (e.g. clamps, sections and dogs). Large contact loads are set up when latching the connector on this wellhead profile with the objective of withstanding internal pressure and wave-induced cyclic bending loads while avoiding hub separation. Fretting fatigue is an additional phenomenon to that of conventional high-cycle fatigue (fatigue crack initiation from the wellhead profile grooves) that should be addressed as part of the design documentation. Methods have been developed to match the key parameters in this contact to a laboratory test. Here, the strength of the effect of each of the matched loading parameters was assessed. Specimens were manufactured from wellhead housing and locking dog steels. The fretting fatigue tests were performed using loads representative of a preloaded connector. Validation of these methods would enable the use of fretting fatigue data determined for one geometry to be used in fatigue life prediction of another.