This article first appeared in Engineering Specifier on June 12, 2017
Drilling for crude oil, as well as the production, processing, storage and transportation of energy, inflicts huge stresses and corrosion on the materials used. Acid-bearing fluids can eat into pipelines, sulphur and hydrogen sulphide can induce corrosion and temperatures higher than 1,100°F can damage the toughest steel. Just as oil and gas workers must adapt to hostile environments, so must the materials used in their equipment. Here, Martin Phillips, Product Manager at Fluenta explains.
An infrastructure of pipes that carry oil and gas is essential to ensure a steady supply of product to both distributors and consumers. To safeguard such a supply, piping materials, pipe shoes and wear pads must be durable and resilient.
A problem in the pipelines
Corrosion (the deterioration of a metal or its properties), poses one of the biggest threats to the oil and gas Industry. Corrosion issues have the potential to affect every stage of an oil and gas site – from casing strings to production platforms, drilling and abandonment. Corrosion is also difficult to control as it can be caused a number of ways. It impacts the oil and gas industry through its impact on capital and operational expenditures (CAPEX and OPEX) and health, safety and the environment (HSE).
If left untreated, drilling mud – or liquid drilling fluid – that has been exposed to oxygen can corrode drilling equipment and pipelines. Water and carbon dioxide can cause severe corrosion of completion strings and acids – used to remove scale – and will attack metal components. On offshore rigs, crustaceans and seaweed may even attach themselves to submerged parts, adding weight that could increase stress related corrosion.
Field operators, pipeline engineers and designers need to be corrosion conscious as the lines and their component fittings could undergo serious material degradation. This degradation will result in the loss of mechanical properties such as ductility and impact strength. This may not only lead to the loss of materials, but also a reduction in thickness, and could lead to the complete failure of a pipeline. Replacing sections of pipe may require a complete plant shutdown at a significant cost.
Corrosion of pipelines can also have a knock on effect on measurement and reporting equipment used by oil and gas sites. For example, on sites where gas flaring occurs, flare gas meters are often installed to measure flow rates. Pipeline corrosion can drastically affect the accuracy of these flow measurements – if the materials are degrading the flow could be interrupted. If inaccuracies are then reported to regulators, oil and gas companies can face significant fines, penalties and even imprisonment in certain parts of the world.
The oil and gas industry has invested heavily in materials and personnel to try and tame corrosion – but it is almost impossible to prevent. The percentage of high pressure and high temperature (HP/HT) wells has dramatically increased, creating the need for special pipes and premium connections to resist high internal pressure and customised alloys to control corrosion rates.
A steely defence
Steel is the most important metal component in the oil and gas Industry, used in the production, processing and final distribution of refined products. Carbon steel is an alloy of iron with up to two percent carbon, increasing the strength of the material and its resistance to corrosion. However, carbon steel can contain trace quantities of other metals, such as nickel.
Get gas moving
Due to their high strength and corrosion resistance, steel and nickel alloys are used extensively in gas processing plants and liquefied natural gas (LNG) plants. Any steel with nine percent nickel content will be particularly tough at extremely high and very low temperatures – and is commonly used in heat exchangers. Heat exchangers remove heat from oil and gas at around 392°F and cool it to 70°F, allowing for the safe transportation of fluid.
Titanium is another of the most versatile and valuable metals used in oil and gas. The addition of titanium to steel alloys also increases the material’s strength, density and corrosion resistance. High strength titanium alloys used in compressor parts are durable and increase the working lives of those parts compared with other steel alloys. Titanium is also highly resistant to seawater, carbon dioxide and hydrogen sulphide corrosion. It maintains its strength at the very low temperatures (-240°F) required to liquefy natural gas. Similar to nickel alloys, it is used in heat exchanger tubing in liquefied natural gas plants and in the linings of the pressurised vessels in LNG tankers.
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