Unlike steel, traditional polypipe is highly resistant to corrosion. However, standard polypipe is vulnerable to chemical permeation in harsh environments. At the risk of oversimplifying complex chemistry, permeation is exactly what it sounds like: one substance's tendency to move through another. In traditional polypipe, gas and liquid hydrocarbon compounds will eventually permeate into and through the plastic pipe wall by the extended exposure to pressures and temperatures.
This process expands and weakens the pipe, making it more susceptible to permeation and early-life failure. To prevent permeation, you have to consider the density of the polymer. In the case of short-chain or aromatic hydrocarbons, the molecular density is very low, which means the hydrocarbons can more easily pass through the plastic wall. Long-chain polyamides, often referred to as nylons, consist of a much denser molecular structure and with more chemical stability.
Due to chemical resistance, nylon has been successfully used for decades in offshore flexible flow lines and risers. In 2015, polyamide-6 (PA6) and polyamide-12 (PA12) products were developed specifically as liners for gathering pipelines, serving as a barrier between the flowing hydrocarbons and the host pipe. Note: the number represents the number of carbon atoms in the polymer chain; the greater the number, the higher the resistance to permeation. Additionally important, the higher number provides more chemical stability at a higher temperature.
Ultimately, this problem has been addressed by composite pipes with a nylon liner. In a single, bound tubular these liners can be engineered to address specific application requirements from temperature to pressure to permeation.Composite pipe by Baker Hughes features a unique design that includes an inner liner for ultra-low permeation. For this liner, there are actually three different options.
1. A nylon PA6 liner, which provides a robust chemical barrier for a range of applications at a lower price point.
2. A nylon PA12 liner, which provides a more substantial chemical barrier at higher temperatures and is the only approved nylon for standalone distribution gas piping systems.
3. A polyphenylene sulfide (PPS) liner, which provides the strongest chemical barrier. With any of these inner liner options, no pressure de-rating is necessary, even at higher temperatures.
These unique capabilities allow a very thin layer of the inner liner material to be produced inside a less expensive liner material offering superior permeation resistance as part of a lower cost solution.
For technical data: Thermoflex Pipe Product Information & Data Sheets
Or you can just read our Product Guide
Questions? Contact us online or call our office at 432-253-7143.