Metallic Umbilicals for Dynamic Application
Authors: Helen P.T. , Ronningen K. 
Published: October 2008

Coming subsea field developments has increase in water depth, in the use of satellite well developments, andinthe useof floating production systems.

Metallic umbilicals has several advantages over the traditional hose umbilicals with respect to permeation, fluid compatibility, hydraulic and mechanical properties.

The introduction of the metallic umbilical for dynamic applications is a cost effective solution for better dynamic umbilicals for future developments.

INTRODUCTION

Umbilicals in general are vital parts of the underwater production technology. But their reliability have been questioned, as many problems have occurred during layingand operation. This is documented in Study of the Performance and Reliability of Hydraulic, Electro-hydraulic and Multi-Functional "Umbilicals" /1/. According to this report, improvements has to be performed in order to increase the reliability of the product. It is also relevant to compare the umbilical reliability with ordinary subsea cablereliability. The latter product group has a remarkable good track record, and "mature" umbilical designs should beexpected to have the same kind of reliability.

One of the problem areas was that the inner liner of the thermoplastic hoses showed compatibility problems with some hydraulic fluids and methanol in special. To comply with these compatibility problems the metal tube umbilicaldesign was developed and installed, first for static applications.

The following summarises what are considered to be the main advantages of metal tubes as hydraulic lines compared to thermoplastic hoses:Fluid (methanol) permeation has been eliminated.Compatibility problems have been reducedCollapse resistance is drastically increased.Favorable response characteristics, especially for long length umbilicalsNo mechanical effect on other umbilical elements when pressurizing.Higher weight diameter ratio gives improved ynamic and seabed stabilityMaximum umbilical manufacturing length without factory jointing is increased, as tube strings are jointed by welding in the laying up process.

Dynamic umbilicals can be installed in several configurations; between a floater and the seabed, between one floater and a rigid structure, between two floaters or from a structure deck to the sea bed. What is common is that in such installations, the umbilicals are exposed to environmental loads and loads from the floater movements.

Up to now dynamic umbilicals have been equivalent to umbilical designs comprising thermoplastic hoses as hydraulic lines. With the above in mind we starfed the development of the dynamic metal tube umbilical. The metallic tube umbilical has already proved itself in several static offshore applications. This paper describes the main steps in the working method and development towards metallic umbilicals for dynamic applications.

Following our introduction of this new generation of umbilicals to the market, a steel tube umbilical for dynamic application, installed on a TLP are now beinginvestigated and will soon be tested. This first installation of a dynamic steel tube umbilical will be performed within two years.

PARAMETERS AND EFFECTS GIVING IMPACT ON UMBILICAL DESIGN AND ANALYSIS

DESIGN ANALYSIS

The dynamic umbilical utilizes the basic philosophy of stranding far more than the static umbilical.