A Comparison of the Expected Long-Term Material Performance of Styrenic Subsea Wet Insulations Versus Polypropylene

ABSTRACT

Styrenic materials, utilized in subsea wet insulation, have been exposed in long-term tests for 12 months at elevated temperatures and pressures in seawater according to ISO 12736:2014. The performance of these materials under this harsh exposure regiment shall be presented and compared to the performance of traditional polypropylene materials.

INTRODUCTION

Styrenic materials for use in subsea wet insulation systems were first introduced to the market in 2010. Since that time, mainly due to their low thermal conductivity that translates into a lower coating thickness as well as great reeling performance even at sub-zero temperatures, they have slowly but surely built a track-record in several subsea projects worldwide: from the Gulf of Mexico, to the Norwegian North Sea, Asia Pacific, and offshore Brazil regions.

Previously, there has not been a well-defined means of evaluating and qualifying new subsea insulation, which has made the introduction of new and innovative systems, such as ones based on styrenic materials, slow and complex. The release of the ISO 12736 standard in 2014¹ has been very beneficial as it provides a clear route for validation of new systems and materials.

In validating a system, the most difficult parameter to demonstrate is the expected long-term performance. ISO 12736:2014¹ presents a means for evaluation of long-term performance via failure mode and risk analysis² through the collection of data for small-geometry material samples under exposure to a conservatively harsh, hot and wet environment. This environment is meant to simulate a worst-case scenario of hot, wet, and deoxygenated conditions; if water encountering the material is not allowed to circulate out into the surrounding environment, such as in the case of burial or water ingress through outer layers, resulting in heating and oxygen consumption of the constrained fluid.

This paper presents the performance of Thermotite^® ULTRA™ ^† styrenic materials, for use in systems operating at up to temperatures of 95 °C and pressures of 300 bar, under hot and wet exposure according to ISO 12736:2014¹. The risks of utilizing these materials in systems are evaluated and are also presented in comparison to polypropylene (PP) materials, which have a long-track record having been in use since the early 1990s.