As a result of environmental and safety considerations the manufacturers of raw thermoplastic material and hose are currently devoting considerable energy and resources to the production of low methanol permeation thermoplastic materials which can be used for chemical injection hoses In subsea umbilical In order to gauge the effectiveness of these materials an investigation Into methanol permeation through thermoplastic hoses has been carried out under the Umbilical - the Future joint Industry umbilical research programme The available permeation test methods were reviewed before selecting a suitable test for measuring very low methanol permeation rates expected from the new materials This was followed by an experimental programme In which the permeation performance of seven candidate thermoplastic hoses was compared with hoses Incorporating currently used core tube materials Most of the new thermoplastic materials tested are shown to exhibit significantly lower permeation to methanol
Methanol is widely used offshore for suppressing the formation of hydrates In oil and gas pipelines The ERC Umbilical Performance and Reliability Report [I] carried out for the Dept of Trade and Industry Offshore Supplies Office (OSO) In 1990 found that over 60% of the chemical injection umbilicals. Investigated were used with methanol
There are very few materials which are not permeable to some degree, and the two principal thermoplastics used for chemical hose liners - namely Polyamide 11 and Thermoplastic Polyester Elastomer (TPE) - are no exception The permeation rate for water and water-based fluids 1s extremely small, and these ecologically acceptable permeates can safely be discharged into the sea through a free-flooding umbilical or its end terminations. Any leakage of a toxic and highly flammable liquid such as methanol, however, clearly causes much more concern, particularly the methanol appears at the platform end of the umbilical Recently there have been concerns from the environmentalist lobby that a significant quantity of methanol may be finding its way into the sea. Furthermore, researchers in the United States have shown that for combined electro-hydraulic-chemical umbilicals the methanol permeant from the chemical hoses can find its way Into the hydraulic hoses, thereby contaminating the hydraulic fluid.
The amount of methanol liberated from the hose will depend upon the materials used and the type of construction. The manufacturers of raw thermoplastic material and hose are currently devoting considerable energy and resources to the production of low permeation thermoplastic materials, spurred on by the competition of stainless steel tubing umbilicals which are becoming increasingly popular. The materials are processed to produce hose core tubes which are either single piece, dual coaxial, or multiple coaxial extrusions incorporating barrier membranes.
This paper describes a programme of work carried out by the Mechanical Engineenng Centre (formerly ERC) on Work Package 13 of the Umbilical - the Future joint Industry umbilical research programme The purpose of the work package was to select a suitable test for measuring very low methanol permeation rates from the new thermoplastic core tube materials, and then to compare the permeation rates of a number of new candidate core tube samples against those for currently used materials