Session: 04-01-06 Flexible Pipes and Umbilicals VI

Paper Number: 108686

108686 - Low and High Cycle Fatigue Performance Limits of Seamless and Seam-Welded Umbilical Super Duplex Stainless Steel Tubes 

Umbilicals provide the critical link between remote subsea wells and fixed or floating production systems, providing control, power and communications services. Super duplex stainless steel umbilicals, designed for both static and dynamic applications, are now the preferred solution in wellhead control systems for deep water projects. The performance of the steel tube umbilicals is typically governed by the low and high cycle fatigue resistance of the seamless or seam-welded small bore super duplex stainless steel tubes which act as the umbilicals tensile members.

Low cycle fatigue loads on the umbilical steel tubes is from plastic strain accumulated during manufacturing and installation operations. The level of accumulated plastic strain can reduce performance and service life, therefore the level of APS needs to be maintained below defined limits to avoid unstable fracture or plastic collapse. High cycle fatigue loads on the steel tubes occurs in service from the umbilical tension, steel tube internal pressure and environmental loads from wind, wave and current.

Umbilical  steel  tubes go through plastic bending cycles during manufacturing  and  installation operations  i.e.  reeling  and  unreeling during  tube  and  umbilical  manufacture, umbilical loadout and umbilical installation over a chute. These bending cycles are the end of significant fatigue loading for static umbilicals. Dynamic steel tube umbilicals are further subjected to bending and tension cycles  in the elastic region. This loading is generated from wave and current motion in  the  water  column both directly and from the  floating  structure from which the umbilical is suspended during  its  service  life.  Therefore,  low  cycle  fatigue  tests  simulating the  plastic  bending  is important to determine the  service  life  of static steel umbilicals and the combination of concurrent low then high cycle fatigue testing is important to quantify the service life of dynamic steel umbilicals.

This paper presents data on the low and high cycle performance of seamless and seam-welded umbilical super duplex stainless steel tubes. The impact of increasing levels of plastic strain on the mechanical integrity and fatigue performance of steel tube umbilicals is presented with the aim of defining an acceptable level of plastic strain that is not detrimental to its integrity. In addition, axial fatigue test data from pre-strained samples are presented and compared with industry standard curves.

Presenting Author: Jamie Fletcher-Woods TechnipFMC Umbilicals Ltd

Presenting Author Biography: xx

Authors:

Hauwa Raji TechnipFMC
Jamie Fletcher-Woods TechnipFMC Umbilicals Ltd
Alan Dobson TechnipFMC