The performance advantages of phenolic resins have been enticing for composites manufacturers and users for many years. The use of these materials has been limited, however, by the process, handling and assembly difficulties they present. This paper introduces an innovative modification which has allowed the development of a filament wound piping system for oilfield applications which previously had been beyond the performance envelope of fiberglass pipe. Improvement in temperature resistance and response to steam exposure, as compared to conventional epoxy products, are of particular benefit. Fabrication innovations are also included which can be used where impact resistance or tire performance are needed.
A break-through in resin technology has occurred which will expand the scope of applications for which fiberglass pipe should be considered. This technological advance involves the use of a polysiloxane modification of phenolic resin.
Various applications exist in the oilfield which, due to temperature limitations of conventional materials, are beyond the performance envelope of fiberglass pipe. The use of phenolic resins, long recognized as a possible answer to this issue, has not practically been possible due to impact, bonding and water content problems. With the introduction of siloxane modified phenolic resin, fiberglass pipe and downhole products can be produced for steam floods, refineries, casing and well screens for use up to 300ºF (150ºC).
RESIN DEVELOPMENT
Phenolic resins, which must be in liquid form for the filament winding of composite pipe, have processing and curing features which have impeded their widespread use. Phenolic resole resins are made by reacting phenol and formaldehyde (with an excess of formaldehyde) using an alkaline catalyst.1 The resulting resins typically need a high content of water or some other solvent to give a workable viscosity for filament winding.
Excellent high temperature resistance.
Good thermal insulator.
Low flame spread.
Low smoke and toxicity when exposed to fire.
The advantages of phenolic resins include:These characteristics make the use of phenolics attractive for high temperature applications and for installations where the piping may be exposed to fire insult.
Water content of resole resins hinders high temperature performance and tire resistance.
Poor adhesion.
Brittleness - poor impact resistance.
Low elongation to failure - resulting in low pressure rating.
The disadvantages of phenolics include:The modification of phenolic resole resin with a siloxane results in significant improvement in these problem performance areas. Siloxane materials are low viscosity, thus reducing the quantity of water or solvents needed in the resin. This reduction prior to the resin being cored yields a polymer with less volatile content. This is seen in weight differential measurements after extended periods at elevated temperatures. See Table 1. Processing of the phenolic material is also improved. Both fiber wetting and cure schedule tolerance are raised significantly.
Improvement in adhesive lap shear strength is shown graphically in Fig. 1. Modification of either the substrate or the adhesive improves the performance. Modifying both the substrate and the adhesive gives the greatest enhancement.2
