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The use of plastic pipes in gas

By The South African Plastic Pipe Manufacturers Association

With the availability of natural gas in neighbouring countries, such as Mozambique and Namibia, and the discovery of offshore gas reserves in South Africa, the gas industry in South Africa is set to undergo rapid expansion.

“In view of these developments, local plastic pipe manufacturers have to ensure that the pipes used in gas pipelines have been manufactured according to stringent specifications and adhere to global standards,” says Jan Venter, chief executive officer of the Southern African Plastic Pipe Manufacturers Association (SAPPMA). This non-profit association represents more than 80% of the plastic pipe produced in South Africa, and focuses its efforts on ensuring pipe systems that are correctly designed, leak-free and durable for long-term use, including the rehabilitation of old pipelines.

Natural gas is a clean burning, more affordable and more secure source of fuel, and is increasingly being looked at as an alternative source of energy for both domestic and industrial use. It burns cleaner than any other fossil fuel, emitting up to 70% less carbon dioxide (CO2) than coal in electricity generation. A modern gas-fired power plant is also 40% more efficient than a coal-fired one. Developing South Africa’s gas pipelines is expected to unlock significant socio-economic and environmental benefits for the country.

According to Venter, pipes made from high-density polyethylene (HDPE) are widely used for the distribution of natural gas, as they have a well-documented inertness to both the external soil environment and to natural gas.

“Extensive testing has taken place over the past 45 years, confirming time and again that the long‑term strength of plastic pipes are unaffected by natural gas and its common constituents — making them the ideal material to use in gas pipelines,” Venter says.

Venter has first-hand knowledge of the potential challenges of a pipeline and why it is crucial to ensure that the materials to be used are up to the task. He was involved in installing the first gas pipeline in Mozambique using HDPE pipe. An 865km cross-border, natural gas pipeline was later installed from the Temane gas fields in Mozambique to Sasol's Secunda Synfuels Operations in early 2000, also using HDPE pipe.

“Like water pipelines, gas pipelines are a long-term investment in infrastructure, and the pipes and the fittings used are therefore required to last in excess of 100 years. HDPE pipes offer numerous benefits for gas pipe installations, such as being lightweight and easy to handle; easy to join; available in a range of sizes and pressure ratings; and have low frictional resistance, with hydraulic properties that remain virtually unchanged over its useful life, resulting in lower energy use and pumping costs,” he explains. Pipes ranging between 20mm and 630mm (as per SANS 4437) are generally used in gas pipelines.

One of the biggest dangers of gas pipelines, however, is the risk of Rapid Crack Propagation (RCP): a rare, but significant catastrophic pipe failure that results in a rapidly progressing crack (typically >300ft/sec) when a pressurised pipeline is subjected to a sudden or intense impact. RCP can also be the result of a pre-existing flaw or crack in the pipe and can occur in most piping materials, including steel and PVC pipes.

“RCP is a concern in piping systems that are used to convey compressed gasses, due to the fact that the rapid energy dissipation from a compressed gas provides the energy required to sustain crack growth,” Venter explains. For this reason, pipes bearing the SAPPMA mark are regularly tested to ensure they meet and exceed industry standards.

SAPPMA has also recently formed a specific task team, headed up by senior technical support engineer at Safripol, George Diliyannis, to investigate the requirements of the current specification, compile a guiding document, and as an industry body, ultimately ensure high standards of pipe manufacture and installation when it comes to gas installations.

Concludes Diliyannis: “The gas industry is fast growing and SAPPMA recognises that it has a responsibility here. South Africa has adopted the latest proven ISO standards for gas pipelines made from HDPE. These standards cover materials, manufacturing, installation and testing. Specifiers and users should ensure that South Africa’s gas pipelines are manufactured and installed according to SANS 4437:2014 to ensure long-term operational safety and pipeline integrity. Gas pipelines will increasingly become an important part of the country’s infrastructure. Extended working lifetimes and uninterrupted supply of gas are therefore essential and will only happen if the pipes and the pipelines are of prime quality.”

 

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