Realistic Evaluation Techniques for Flexible Pipe Polymers Exposed to Wellbore Fluids
Authors: Wolfe G.K. , Hines W.F. , Papay J.J. , Pagilagan R.U. 
Published: October 2008

Because of an industry need for improved polymer material used in flexible pipe liners when exposed to sour gas, a research program was undertaken. The goals of the program were to develop realistic evaluation procedures for screening purposes and then, to evaluate several alternate polymer materials to the currently used standard, RILSAN® Nylon 11 to see if improved performance could be obtained E. I. DuPont developed the polymers, molded the test coupons and conducted the materials characterization tests, while SwRI developed the procedures, equipment and conducted the environmental exposure tests.

Six different material combinations were subjected to sixteen (16) environmental/temperature/stress combinations in the laboratory. From these 2000 hour tests four polymers were subjected to the most aggressive environment for 12,500 hours. Curves of the change in mechanical properties with increased exposure time indicate that there we, at least, two alternatives to the currently used polymer that provide as good or better properties.

INTRODUCTION

The use of flexible pipe to replace steel pipe in riser, flowline and other applications within the petroleum industry is gaining increased popularity. Very deep water production and marginal field production make the use of flexible pipe more than competitive. The possibility of reuse, demonstrated by Petrobras, adds even more weight to the decision process in favor of flexible pipe. Neffgen1 has identified many of the attributes of flexible pipe that encourage its use. Some are:can accommodate large relative motionsprovide high corrosion resistancereduce installation time and costhas high dampening coefficientshas high resistance to dynamic loadsaccommodates undulating seabed conditionspermits remote connections to subsea production equipment With these and other attributes being discovered as applications are identified, the future of flexible pipe as a key element in petroleum operations is very bright.

As applications for flexible pipe grow, the need to provide improved and more cost effective materials for pipe construction will grow. There are currently, at least, eight companies that are producing, or have the capability to produce flexible pipe. With over seven hundred (700) miles of flexible pipe currently in use and projections for several thousand miles to be in use by the year 2000, the entrance of other companies into the market and expanded need for raw material is virtually assured.

In looking at the market and the various combinations of materials available, DuPont had identified several possible candidates. However, they were unsure on how to evaluate the materials. Several manufacturers, operators and oil companies were contacted about how to best conduct the evaluation with almost as many answers as people contacted. There was not (or is not) any standard for the evaluation of flexible pipe or flexible pipe materials. Several possible standards are currently in work but at that time, there was no real information to go on. Therefore, SwRI and DuPont decided to proceed with a stepwise program of continuing complexity to evaluate the materials. The purpose being, to drop out some materials as more information is known about them.