ABSTRACT A prograrnme of experimental work has been carrled out under the "Umbilicals - the Future" joint Industry umbilical research project, In which the behavior of thermoplastic hoses In response to rapid pressure changes has been examined in detail The hose characteristics which have been investigated include steady state volumetric expansion, ageing, visco-elasticity and dynamic volumetric expansion Simulation results are presented which show the importance of correctly accounting for these effects when designing subsea well control systems, particularly for systems where there is no subsea hydraulic accumulation INTRODUCTION Hydraulic umbilical hoses used for direct hydraulic and pilot hydraulic operation of subsea production control systems have traditionally been required to exhibit minimal volumetric expansion(VE) under pressure to minimize the system response time. This rapid operation is now a feature required for direct hydraulically-operated pipeline safety valves The growth in popularity of electro hydraulic subsea production control systems over recent years has, however, provoked fresh Interest in the behavior of the umbilical hydraulic hoses when under pressure In such systems the volumetric expansion of hoses can be utilised to supply the peak flow requirements of individual Christrnas tree valve actuator openings Using the hose as a storage element can eliminate the need for local subsea accumulation, which is an attractive option for reducing costs and improving system reliability Thermoplastic hoses exhibit a visco-elasticity time-related response to changes In pressure, whereby after initial pressurization of a hose, the pressure decays to a stabilized level over a period of time as the hose gradually dilates A similar time-related contraction of the hoses occurs during de-pressurisation Thus the hydraulic control hoses within the umbilical make relatively poor accumulators, unlike the conventional bladder type accumulator, the hose wall movement, is both damped and hysteretic Where hoses represent the only hydraulic accumulation with the system, there is the danger that the supply pressure to the subsea control module directional valves will momentarily collapse during the opening of large capacity tree valve actuators System designers, therefore, need to know both the static volumetric expansion of the hoses, and their dynamic expansion relaxation characteristics In response to pressure changes The system designer's task is complicated further by the phenomenon of hose ageing, which is well known but little understood Over the period of a few weeks at pressure the volumetric expansion of thermoplastic hoses has been found to decrease, indicating an increase In the stiffness of the hose construction Thus, a control system which utilizes hose volumetric expansion to supply the flow requirements of individual tree valve openings may perform satisfactorily during commissioning, yet be found wanting after a period In service Because of this uncertainty, control system suppliers often feel compelled to fit subsea accumulators, even though they may not in practice be necessary This paper describes the work carried out under Work Package 12 of the "Umbilicals - the Future" joint Industry funded programme

ABSTRACT A comprehensive series of bend-over-sheave fatigue tests has been carried out on a single design of electrohydraulic umbilical to establish the effect of a number of factors on the measured life The factors which were examined were axial load, hose pressure, sheave diameter and wrap angle. INTRODUCTION As part of the Joint Industry Project "Umbilicals - the Future", a comprehensive series of tests has been carried out on a single design of electrohydraulic umbilical The test regime which has been examined is "bend-over-sheave" (BOS) also known as "cyclic-bend-over-sheave" (CBOS) In this style of loading the umbilical is passed around a sheave wheel (or arc of a circular former) with a tensile load applied If the umbilical is passed backwards and forwards around the sheave, the umbilical is subject to an alternating (cyclic) bending, which can lead to fatigue failure of the umbilical components Bend-over-sheave loading has been generally identified as the most onerous to which an umbilical designed for static service is subject. This loading arises during installation, when, at the lay vessel, the tension occurs by virtue of the weight of the umbilical in suspension to the sea-bed, and the motion arises around the overboarding sheave due to the vessel motion Although in normal installation operations has will not result in a large number of cycles, it is possible that in circumstances where the operation has to be halted and the vessel remains hove-to for a period of time, significant numbers of load cycles can arise A total of twelve specimens has been tested, enabling a number of variables to be examined REVIEW OF APPLICABLE LITERATURE There is a wealth of literature in the field of cables and wire ropes as these are both very widely used. However, papers which address the area of bend-over-sheave testing of cables (rather than ropes) are rare The fatigue behaviour of ropes in the bend-oversheave regime has been widely studied, and some of the results, and mechanisms would seem to have applicability to umbilicals The most comprehensive paper which addresses the issue of bend-over-sheave testing of cables and ropes is Gibson (Ref 1) This paper describes the concepts involved in the p l m g of bend-over-sheave testing, and defines a suitable terminology Important definitions include the concept of short stroke tests and long stroke tests, the difference between them being whether the stroke of the cable motion is less than or equal to the length of the cable to sheave contact arc (short stroke) or greater than the length of the cable to sheave contact arc (long stroke) The identification that the cable has three possible types of zone, namely zero-bend zone (ZBZ), single-bend zone (SBZ) and double-bend zone (DBZ) are also discussed, with the length, and number of zones depending on the type of test and stroke length

ABSTRACT The paper reports the analytical part of a development project into the design and fatigue performance of composite umbilicals, carried out under Work Package 2 of the "Umbilical - The Future" joint industry funded project A computer model of an electrohydraulical, symrnetrical umbilical subjected to various axial loads and bent around sheaves of different diameters has been developed This model entitled Gneg2 calculates the relative sliding between the cores and stresses due to the effects of bending, axial load and friction INTRODUCTION Over recent years, umbilicals have been increasingly used in many off-shore applications worldwide for subsea control, chemical Injection etc The failure of these components in a remote subsea installation can be extremely expensive both in lost production and rectification Unfortunately, insufficient knowledge of the complex behaviour of umbilicals has often led to defective design, manufacture, installation and operation A report from the Engineering Research Centre, dated July 1990, revealed a significant number of problems associated with unbilicals [3] It was concluded that some form of planned R&D was necessary if the industry was to improve umbilical reliability From 1985 to 1992 BP Norway Ltd, ABB Norsk Kabel and EFT, which is a part of the SINTEF Group. Norway, ran a project in order to achieve a better understanding of the behaviour of umbilicals and to try to reveal factors having a great influence on the life of umbilials It was decided, as a start, to concentrate on electrical umbilicals, both unarmoured and armoured, and to try to determine the stresses and the fatigue life of an axially loaded umbilical running back and forth over a sheave If this problem could be solved it was expected that more complex umbilicals and other types of bending problems could be included in later phases The theory developed, which was implemented in a computer program entitled Grieg was able to describe and calculate the internal movements and forces in all-electric umbilicals [l] and [2] However, there was a need to extend ths theory to the more common umbilical configurations containing both electrical cores and hydraulic hoses In 1993, when the R&D programme "Umbilicals - The Future" started, it was decided to continue the research work within a Work Package 2, called "Umbilical Modelling and Design" All results and expenence gained in the former project was made available to the new project This paper is the first of two papers which give a summary of work, description and results from both these projects The problems were attacked both analytically and experimentally simultaneously as the analysis required knowledge of parameters which have not previously been studied or quantified The analytical work, which will be presented in this paper, was based on several assumptions Some of these could be tested directly, others could only be tested indirectly by observing which assumptions and parameter values gave correspondence between calculation and test results Flgure 1 Investigated umbilicals (Available in full paper) Figure 1 shows the Investigated umbil~calsd unng the first project [I]