Polyethylene liners offer a good combination of chemical resistance, installation friendliness, and cost- effectiveness, but their application at higher temperatures is limited, particularly in hydrocarbon service. While polyethylene is the standard for liners for buried carbon steel line pipe in the oil and gas industry, other polymeric liners such as polyamide 11 and polyvinylidene fluoride are standard for flexible pressure pipe in the offshore industry. In addition, the chemical process industry routinely uses fluoropolymer lined steel joints, valves, and elbows for demanding corrosive service. This investigation is an attempt to identify some of the polymeric materials which have been shown to be useful either as liners for non-traditional pipe or as liners for individual fittings and short runs of pipe and examine their utility for long pipeline rehabilitation.
It is a challenge to those involved in the use of polymers for corrosion control to coordinate the beneficial service properties with the often unfamiliar handling properties. It is common, and frustrating, to read publications of the high performance capabilities of a new class of polymers yet fail to see any mention (or later any market development) of corrosion control applications. Size and Growth of the U.S. Polymer Industry The polymer industry in the United States, according to the latest figures available, is $274 billion.' The breakdown in terms of industries is given in Table 1, with a distribution chart of polymer types given in Figure 1.
The growth in the polymer industry, by dollar amount, is 55% since 1991. Since 1974, shipments have increased by an annual rate of 4.1% as compared to an average annual rate of 1.3% for the overall manufacturing industry over the same period. As an industry, plastics rank fourth domestically behind only motor vehicles, petroleum refining, and electronic components. Along with the increase in volume and the greater number of applications for existing commodity plastics, polymer science has produced a great number of new plastics engineered for superior properties.
The large and growing market for plastics is largely based on the ability of plastics to produce cheaper, lighter, more convenient versions of products and packaging for products. The raw tonnage of polyethylene for garbage bags, shrink wrap packaging, and containers dwarfs the amount used for pipelines and corrosion control; less than 5% is produced as tubes for any application. Nevertheless, plastic piping systems are well established in the world economy. PVC pipe for sanitary and storm sewers alone is produced at a rate of more than 500 million lineal feet annually, and production of polyethylene pipe in 1998 was 1.1 billion pounds. Limitations of Current Liner Technology
The use of plastic pipe liners for corrosive service has been well established in a variety of industries. Liners for gathering and transmission pipelines currently in service are almost exclusively polyethylene, generally high-density polyethylene (HDPE), due to its combination of excellent chemical resistance, low cost, ease of handling, and wide availability.
However, HDPE liners provide a limited service envelope. In hydrocarbon environments, there can be severe service limitations above temperatures as low as 125F. Even in the absence of hydrocarbons, liners are limited to applications below 160F. While this range covers the vast majority of pipelines currently in service, the high temperature pipelines are in greater need of corrosion protection. Thus, while the fraction of pipelines operating at high temperatures is small, the need in this area is very high.
There are also many practical
