An Investigation Into Fretting Behaviour in Pressure Armor Wires of Unbonded Flexible Pipes

Abstract

The possibility of fretting damage in pressure armor wires of flexible pipes has been investigated. A novel experimental facility which is capable of simulating nub/valley contact conditions with dynamic slip, representative of actual pipe loading, has been developed. The test setup is equipped with a state of the art data acquisition system and a controller with transducers to measure and control the normal load, slip amplitude and friction force at the contact in addition to the hoop stress in the wire. Tests were performed with selected loading and the fretted regions were examined using an optical microscope. Results show that the magnitude of contact loading and the slip amplitude have a distinct effect on surface damage. Surface cracks originated from fretting scar were observed at very high contact loads in mixed slip sliding while surface damage predominantly due to wear was observed under gross slip. The position of surface cracks and the wear profile have been related to the contact pressure distribution. The evolution of friction force and surface damage under different slip and normal pressure conditions are presented. The effect of a general grease lubricant on friction behavior is also discussed.

A global-local fretting analysis methodology and design study for the pressure armour layer of dynamic flexible marine risers

“…Although this work reviewed the issue of fretting in detail, the nub-groove contact loading conditions were not quantified. Perera et al (2007) performed fretting wear tests on pressure armour wire to quantify the fretting behaviour; however, the loading conditions used were not based on global riser analysis. Féret and Bournazel (1987) presented a theoretical approach to calculate stresses, contact pressures and slip between tensile armour layers of flexible pipes under axisymmetric loading.…”

“…However, the relationship between global riser loading conditions, such as internal and external pipe pressure, vessel motions, wave and current loads, and local nub-groove fretting conditions, such as contact pressure and contact slip is unknown. Perera et al [8] presented an experimental method for fretting of the pressure armour layer of unbonded flexible pipes.…”

High Pressure Flexibles Pipes – Knowledge and Qualifications at 15 kpsi, 17.5kpsi and 20 kpsi Design Pressure

“…Laboratory tests and finite element calculations are performed [7]. With this construction, the potential for fretting fatigue between the two pressure armor layers has to be assessed.…”

A combined wear-fatigue design methodology for fretting in the pressure armour layer of flexible marine risers

“…Burke and Witz [10] presented an excellent review of the problem at an industrial conference. More recently, Perera [19] presented an experimental investigation for fretting of the pressure armour layer of unbonded flexible pipes.…”