ABSTRACT

The need for unproved materials for control and chemical injection liners in umbilicals has been recognized for some time. The materials, winch have been in use for many years, NYLON 11 and HYTREL* bath have same limitations in the two critical areas of a) long term chemical reliability with hydraulic fluids and injected chemicals, and b) permeation of methanol.

As a result of the h3w.tryfs desire to overcame these short comings, work has been continuing for same time on alternative compositions which would address the problems.

This paper describes sane new materials and hose liner designs which have been developed, and which are currently being evaluated m finished hose constructions. In particular, two multi-layer designs have been developed which appear to offer significant improvements aver existing hose liner materials

INTRODUCTION

High pressure thermoplastic hoses have been in use for more than 15 years in umbilicals for hydraulic control and chemical injection services to subsea wellheads. The length and number of these umbilicals has been messing steadily as technology has developed towards the adoption of more subsea completions at greater distances from the mother platform.

As the use of umbilicals has increased, so has the attention paid to the design and testing of the umbilicals and their component hoses. The experiences of past installations, as well as the analysis of results from many laboratory tests which have accumulated aver the years, has led to a much greater understanding of the critical requirements of umbilical hoses, and in particular the hose liner (core tube) constructions. These requirements can be categorised in the following way : -

  • Long term compatibility with a) hydraulic (control) fluids b) injection chemicals (including methanol)

  • Lowest possible permeation rate with respect to fluids, in particular methanol

  • Excellent long term mechanical properties, including resistance to creep.

  • Cleanliness - in terms of non-contamination of the fluids due to extraction of components from the liner material.

In the past, two materials were exclusively used for hose liners: Nylon 11 and polyester elastomer (HYTREL*). Each of these materials has its strengths d weaknesses in the areas of chemical compatibility; in particular, Nylon 11 tended to be favoured where water/glycol fluids were commonly used, whilst HYTREL* had its strengths in the hydrocarbon based fluids. However, it has become clear that the industry demands greater guarantees of long term overall compatibility to a wide range of chemicals, as well as much reduced barrier properties with respect to methanol permeation.

CHEMICAL COMPATIBILITY

It is not the purpose of this paper to go into detail about compatibility of hose liners with the wide range of control and chemical injection fluids that are used in umbilical hoses. Suffice it to say that the major control fluids used today tend to be water/glycol based, with same mineral oil based fluids still evident; also the range of injection chemical used can extend in relatively inert fluids to same of the more aggressive anti--commission and de-scaling chemicals. In addition, methanol is injected in large quantities via umbilical hoses into the wellhead, for flushing operations.

This content is only available via PDF.
You can access this article if you purchase or spend a download.