Aging in natural gas activates the relaxations of polymer melts

Overview & Synopsis

Although cast iron pipes carrying natural gas have been in service for several decades, they are prone to corrosion, cracks, and leaks. Polymeric materials such as polyethylene (PE), polyamide (PA) and polyvinylidene difluoride (PVDF) can serve as internal structural liners because of their high corrosion resistance, high strength-to-weight ratio, and impressive mechanical durability in hydrocarbon-rich and high-pressure environments. However, the impact of hydrocarbon environments on the properties of polymer liners is not yet fully understood. In this project, we characterize the properties of these materials after exposure to hydrocarbons at elevated temperatures and pressures, and over long periods of time to assess the stability of these liners in the presence of natural gas and contaminants. Dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy (FTIR) were performed on both pre-aged and post-aged samples. Notably, the storage modulus indicates that the polymers generally maintain acceptable mechanical and chemical stability under typical natural gas compositions. However, using time-temperature superposition (TTS) indicates that hydrocarbon aging accelerates polymer relaxations and may lead to reduced mechanical performance. Thus, the activation energy governing polymer relaxation was identified as a sensitive indicator for benchmarking polymer performance and degradation. This minor change in polymer properties demonstrate that they are a viable alternative to cast iron for use as pipeline liners. However, hydrocarbon mixtures may contain reactive or corrosive contaminants. The next step of our study will focus on including these contaminants to observe their effects on mechanical and chemical properties and the activation energy.