Effect of zinc coating and grease on the fretting fatigue life of steel wires used in spiral steel ropes

Spiral strand ropes are often used as mooring lines in offshore industry. These ropes are intended to be used in tension only. Cyclic bending is prohibited as it can produce fretting fatigue between the steel wires. Yet, this fretting fatigue is little known, in peculiar when zinc coating and grease are present. We performed numerous fretting fatigue tests on steel wires, including or not the zinc coating and grease. The fretting fatigue loads come from a detailed finite element model of a spiral rope, where the wires are individually modelled. The zinc coating alone little affects the wires lifetime. The grease alone has a beneficial effect or a negative one, depending on the load.

However, when both zinc coating and grease are present, the fretting fatigue life is improved. There is a synergy between these two components that improves the mechanical behaviour of the rope. Yet this positive effect is load dependent and varies from nearly zero to very beneficial

Author(s): S.Montalvo, M.Martinez, S.Fouvry