A Direct Measurement System to obtain the Thermal Conductivity of Pipeline Insulation Coating Systems under Simulated Service Conditions
Authors: Haldane D. , van der Graaf F. , Lankhorst A.M. 
Published: October 2008

This paper describes a long term programmer of research which has resulted in the development of a simulated service test facility incorporating a direct measurement system which can be used to confirm the heat transfer characteristics of subset factory applied and field joint insulation coating systems produced under normal production conditions. The simulated service test was originally developed by Shell Research at their Thornton Research Centre in the UK in the late 1980's. To date these test facilities and accompanying procedures have been successfully used by industry to study the behaviors of thermal insulation coating systems on lengths of steel pipe internally heated to temperatures up to 140 °C and when subjected externally to hydrostatic pressures up to the equivalent of water depths of 1450m under real time conditions. It is already becoming apparent that the specialized form of the heat flux measuring device which has been developed during the course of this research programmer can be used in other applications.

Introduction

Traditionally externally applied coating systems for offshore pipelines, subsea flow lines, steel catenary risers, etc. have been used mainly to protect the steel pipe from attack by the surrounding seawater environment. Normally the majority of the length of such pipelines/flowlines/risers are protected by a coating system applied under factory controlled conditions whereas the field joint areas within the factory applied coating system are protected by a coating system, applied under field conditions, which may comprise of entirely different types of material.

Subsea developments have placed a requirement on the development of coating systems for flowlines which will provide them with protection against corrosion attack, heat loss, instability under hydrodynamic loadings, mechanical damage from third party activities, etc., often in combination. These coating systems are required to operate in situations in which the produced fluid temperatures are increasing in excess of 140°C and/or in water depths in excess of 1500m.

Solutions to satisfy these often conflicting demands are not readily available so new materials need to be either identified or developed and built into cost effective thermal insulation coating systems. This requirement applies not only to factory applied coating systems but equally to field joint coating systems. The requirement to continually develop coating systems for pipelines/flowlines/risers has emphasised the need to have in place approaches, including test procedures, which ensure acceptable levels of quality control and can also be used to establish whether in fact they will be fit-for-purpose.

The significance of the difference between quality control testing where the constituent parts of an insulation coating system are tested under standardised conditions and fitness-for-purpose tests where either the constituent parts of a coating system or the complete coating system are tested under inservice conditions must be emphasised. The acceptance criteria to be adopted in these test programmes should reflect the composite nature of these coating systems.

It is therefore important to be able to predict the likely extent of the damage or disruption to flowline coating systems resulting from the mechanical loadings, etc. experienced when pipelines/flowlines/risers are being installed and also throughout their design life when they are in-service on the seabed.

However, not all coating systems are suitable for all fields, and a proper understanding of the requirements and the systems is critical.