By Nouran Ashraf
Pipelines are one of the main elements of the oil and gas infrastructure. It acts as the main transportation system for all kinds of energy products; natural gas, biofuels, and liquid petroleum. There are two main types of materials in which pipelines are made of metal, such as Steel, or non-metal, such as plastic. Both kinds of Pipelines serve the same purpose, however, steel pipelines are the type commonly used worldwide. The development of non-metal pipelines may lead to the question of whether oil field operators should use plastic pipelines to structure their infrastructure instead of steel.
Pipelines exist throughout the world; they vary by size, types of products transported, and the material they’re made of. Pipelines serve three main purposes: gathering lines, which bring crude oil or natural gas from nearby wells to a treatment plant or processing facility, transportation pipelines that transit the outcome products like oil, gas and refined product between cities or countries, and distribution pipelines which convey the products to the end users.
Pipelines weren’t always used as a means of transporting energy products. Long before wood and steel pipelines were introduced to the public, oil was maintained in whiskey barrels and transported from wells to railway stations using horses. In 1865, wood and metal pipelines were introduced as a replacement of barrels. Later, in the beginning of the 20th century, cast iron was used in creating the pipelines for the oil and gas infrastructure that was later again replaced by steel as the material of choice, mainly because of steel’s strength and flexible nature. The main types of metal steel pipelines mostly used in the oil and gas industry are carbon steel, killed carbon, alloy steel and stainless steel. The main differences between each type depend on the traces of elements within each type and the temperature, pressure, and corrosion conditions where they would be placed. Non-Metal Plastic pipelines started to gain popularity in the 1990s since the interest in non-corrosive pipelines to be used in a lower pressure and temperature conditions has arisen
Non-Metal Pipelines Introduction
Plastic pipelines are characterized by corrosion resistance, light weight, and is commonly used in moderate temperature and pressure applications. The most popular types of non-metal plastic pipelines are polyethylene, polypropylene, UPVC and HDPE. They provide a corrosive-resistant pipe for oil and gas applications with the strength for replacing steel pipelines in low- and medium-pressure circumstances. Even though Metal steel pipelines are still the main type of pipelines widely used worldwide and may still be the first choice for oil and gas companies, plastic pipelines are starting to be favorable to the oil and gas field operators within the applicable environments.
Elements to Consider
There are many elements to be considered while building the pipeline’s infrastructure within the oil and gas industry, the geographical and environmental conditions including the temperature and pressure where the pipelines would be placed, type of fluids that the pipelines carry, the means of transportation to be used, the financial capabilities of the oil and gas company and its budget for the planned projects, the lifespan of the pipelines that ensures the sustainability of the project without the need for replacement.
BOP Piping Planning Management Team at Siemens AG Mohamed Noaman explained to Egypt Oil&Gas that “choosing the material of the pipeline’s infrastructure within the oil and gas industry depends on many parameters including the project’s budget, design, type of the process, location, and integrity and lifetime.”
Geographical Conditions
Temperature and Pressure
Metal pipelines have the ability to withstand low and high pressure and temperature ranges. They can survive a pressure range from 30 up to 40 bars and temperature ranges up to up to 100° C, while the non-metal plastic pipelines have a lower tolerance to higher pressure and temperature in comparison to its metal alternatives. There are some applications where they can be used for fairly higher temperatures, but metallic pipelines such as steel pipelines can withstand much higher temperature. The plastic pipelines can’t be used in very high-pressure applications also since they have weak intermolecular structure.
Chemical Resistance
Metal Steel pipelines are suitable for both hot and wet applications such as river crossings and rough terrain but the most significant disadvantage of steel pipelines is corrosion; external corrosion affects both buried pipelines and above-ground pipelines. Internal corrosion of steel pipelines is a major dilemma in the oil and gas sector due to the high level of environmental costs and repercussions of spillage of the oil. The Canadian Energy Pipeline Association (CEPA) released a report stating that in 2015 about 16 barrels of crude oil spilled from pipelines, meanwhile, 121.3 million cubic feet of natural gas leaked due to corrosion related reasons in Canada.
Since replacement of pipelines can be financially challenging for the operator, companies have been solving corrosion by different methods mostly coating the steel pipelines with anticorrosive materials that provide an effective insulation against the environment which must be strong enough to tolerate the operating temperatures, show resistance to the soil, and have the ability to withstand physical handling.
Senior Pipeline Design Engineer at Petrojet, Mr. Farouk el Batawy noted to Egypt Oil&Gas that “Corrosion is one of the main challenges that face the metal pipelines infrastructure; there are four different methods that oil and gas companies adapt to fight it which are protective coatings and linings, cathodic protection, materials selection, and inhibitors. Coatings and linings are often executed in parallel with cathodic protection systems to achieve the most cost-effective protection for pipelines. Evaluating the environment in which a pipeline is or will be placed is essential to corrosion control since modifying the environment in the first place by reducing moisture or improving drainage, can be a simple and effective way to reduce the potential for corrosion while using corrosion inhibitors can extend the lifespan of the pipelines, prevent system shutdowns and failures, and avoid product contamination”
Meanwhile, using non-metal pipelines like HDPE can avoid the corrosion issue in the first place as it is rustproof, break-resistant, and corrosion-free. The water leakage percentage is zero. PE Pipelines have a geographical advantage that allows them to withstand harsh chemical environments since they are abrasion resistant and are suitable for the solid environment in mining fields. It provides long-term resistance to a temperature and soil shifts, bending, weathering, internal pressure, direct burial, point loading and squeeze-off. HDPE is resistant to hydrous solutions of acids, alkalis, and salts as well as to a large number of organic solvents. Plastic pipelines are also known for their flexible nature: Gas distribution systems are capable of surviving severe ground shifts, especially from earthquakes, when they are made from fused PE pipelines.
According to EL Battawy, in 2010, Qarun Petroleum Company replaced all the carbon steel wellheads water injection systems with HDPE, GRE (Glass reinforced epoxy) as the carbon steel wellheads were damaged due to the saline water and the higher corrosion rates.
Technical Conditions
Strength
Metal pipelines has higher strength when compared to plastic pipelines which have lower strength since the support span for these pipelines is not relatively high, which may lead to the placing of additional civil structure for proper support of these pipelines.
Design Considerations
Plastic pipelines including HDPE and other thermoplastic piping does not work well when exposed to ultraviolet light. This effect is commonly called ultraviolet (UV) degradation. If plastic pipes are stored outdoors, they may require protection from weathering. On the other hand, Metal steel pipelines have excellent benefits including excellent stress crack resistance to natural gas and its contaminants, low permeation to methane and hydrogen, high Hydrostatic Design basis rating at 20°C, 60°C and 80°C, superior impact resistance, squeeze off, and dependable Ultra-Violet performance for outside storage.
Transportation
When it comes to transportation the main challenge facing the steel pipelines operators is its heavy weight that makes it more difficult to transport and install. It requires more manpower, equipment, and energy, while non-metal pipelines lightweight is often more cost effective to transport and install and requires less manpower since non-metal pipelines like PE is easily installed without heavy lifting equipment joined by heat fusion or mechanical fitting. PE pipe is produced in straight lengths up to 50 feet long and coiled in diameters up through 6-inches, making it easy to install and reduces the numbers of joints used in the piping system.
Safety
The metallic materials used in creating pipelines like the Carbon steel have the ability to withstand the heat from the higher temperature environments that give it the ability to withstand fire hazards, while using plastic pipelines can subject the operator to higher risks of fire hazards due to the static charge accumulation. “The metallic materials (Carbon steel, low temp., Alloy Steel and S. Steel) is prioritized in the oil and gas pipelines infrastructure due to the codes obligated by The American Society of Mechanical Engineers (ASME) and The National Fire Protection Association (NFPA) that indicates the mandatory usage of the Carbon steel in all the main oil and gas processes, firefighting systems, some different utility systems too, since the carbon steel has the ability to withstand higher temperatures in case of fires to limit safety risks” explained El Battawy to Egypt Oil&Gas.
Financial Conditions
Oil and gas companies looking for cost reduction solutions while developing their oil and gas infrastructure within low and medium temperature and pressure conditions might consider non-metal pipelines such as high-density polyethylene (HDPE) pipelines as an alternative to steel pipelines within the applicable conditions. PE pipe installations have long- term cost advantages due to its physical properties, leak-free joints, and low maintenance costs also the life cycle for PE pipe can extend from 50-100 years, which gives it a long term sustainable advantage as the operators can avoid replacement of the pipelines for generations to come.
Proposals and Contracts Engineer at Enppi Ahmed Salah Eldin, noted to Egypt Oil&Gas that “the choice between metal and non-metal pipelines depends on many technical factors but if the technical factors allows the operator to choose between both materials and the company is looking for a cost effective solution for their pipelines infrastructure, plastic pipelines will be the matter of choice as it costs less than its metal alternatives.”
Environmental Conditions
Non-metal plastic pipelines like PE doesn’t produce hazardous levels of toxins into the air during production, fusion or into the ground or water when operated, making it eco-friendly. Meanwhile, metal pipelines that suffer from corrosion can lead to spillage of oil that releases toxic chemicals negatively affecting the surrounding environment.
At the end, Non- Metal plastic pipelines can’t replace steel pipelines in higher temperature and pressure environments, but they can work efficiently within medium and low temperature and pressure providing an alternative for metal pipelines operators’ struggling with issues like corrosion. Metal pipelines provide a great range of benefits due to their higher strength and flexibility and ability to withstand higher pressure and temperature while non-metal pipelines have the advantage of the corrosion resistance, light weight, cost reduction and long-term sustainable advantage that will enhance the strength of the oil and gas infrastructure of the oil and gas corporation.
