Sourcing equipment to withstand hostile oil and gas operations
29 November 2017
In this article, Martin Phillips of flow control specialist Fluenta looks at the effects and costs of pipeline corrosion and some of the materials and methods that can be used to increase durability and resilience.
An infrastructure of pipes is essential for a steady supply of oil and gas to distributors and consumers. But drilling for crude oil, as well as the production, processing, storage and transportation of energy, inflicts huge stresses on piping materials. Acid-bearing fluids will eat into pipelines, sulphur and hydrogen sulphide can induce corrosion and if temperatures are higher than 600 degrees C - steel can become brittle.
Corrosion – the deterioration of a metal or its properties – poses one of the biggest threats to the Oil & Gas industry. From casing strings to production platforms, drilling and abandonment, corrosion can affect almost every stage of oil and gas production. According to ODEE - an Oil & Gas Industry journal - as offshore exploration moves into deeper and more hostile waters the potential impact of corrosion increases, with the total annual cost of corrosion estimated at almost $1.372 billion.
Counteracting the effect of corrosion is made difficult by its causes – of which there are many. 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 – will attack metal components. On offshore rigs, even crustaceans and seaweed add weight that could increase stress-related corrosion by attaching themselves to submerged parts.
The cost of corrosion
Oil and gas companies must be conscious of the corrosion threat, as pipelines and their component fittings could undergo serious material degradation as a result. Severe degradation can lead to the loss of mechanical properties such as ductility and impact strength, reduced pipe thickness, or even complete pipeline failure. If sections of pipe need to be replaced, engineers may require a complete plant shut down to carry out repairs – at significant cost to the operator.
In addition to impacting capital, pipeline corrosion can have a knock on effect on the measurement and reporting equipment often used by oil and gas sites. Environmental authorities around the world increasingly require the Oil & Gas Industry to monitor and record emissions, flowrates and gas composition. Almost every offshore production facility now has flare gas meters installed to control mass balance, prevent leakage and monitor CO2 emissions. Pipeline corrosion can drastically affect the accuracy of these flow measurements – if materials are degrading, flow can be interrupted and measurements across the pipe’s diameter will be inaccurate. If these inaccuracies are reported to regulators, oil and gas companies can face significant fines, penalties and even imprisonment in some parts of the world.
The Oil & Gas Industry is investing heavily in materials and personnel to curb the effects of corrosion - but it is almost impossible to prevent. With the percentage of high pressure and high temperature (HP/HT) wells increasing, there is a heightened need for pipes and connections that can resist high internal pressure and customised alloys to fight off corrosion.
When oil and gas assets start to age or degrade, there is an increased likelihood of major incident. Studies show that more than 60% of Hydrocarbon (HC) leaks are caused by ageing processes such as fatigue and corrosion. Fire and explosions can be a serious consequence of HC leaks – which could result in substantial revenue loss and even the loss of life.
A steel solution
Arguably the most important metal component used in the Oil & Gas Industry, steel plays a part in the production, processing and final distribution of refined products. Carbon steel - an alloy of iron with up to 2% carbon - is even stronger and more resistant to corrosion.
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 9% 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 200 degrees C and cool it to 21 degrees C, allowing for the safe transportation of fluid.
The addition of titanium to steel alloys further increases the material’s strength, density and corrosion resistance. High-strength titanium alloys - used in compressor parts - are particularly durable and increase the working lives of parts. Titanium is also highly resistant to seawater, carbon dioxide and hydrogen sulphide corrosion. It maintains its strength at the very low temperatures (- 151 degrees C) required to liquefy natural gas.
Engineering systems for handling liquefied natural gas are designed for an operating temperature of -163°C. Metals for use at such cryogenic temperatures need to comply with demanding mechanical and physical properties. The ductile strength of metals tends to increase at lower temperature, but LNG applicable metals need to have sufficient strength in service, but also be strong enough to be formed and fabricated at ambient temperature.
Corrosion on the cold front
In addition to the threat of corrosion, the materials and metals used in oil and gas equipment must withstand extreme heat or cold. In extreme cold, pipeline systems may experience component failure. This can be caused by meter damage from snow or ice shedding off rooftops, falling trees due to ice accumulation or fractures due to the expansion of moisture trapped inside components and equipment.
Copper and its alloys – including bronze - have excellent electrical and thermal conductivity and cryogenic, or cold-resistant, properties. These metals are commonly used in valves, stems, seals and heat transfer applications because of their resistance to temperature change. A bronze alloy with traces of nickel and aluminium can also be used in wellheads and blowout prevention valves to protect processes from the effects of extreme heat or cold.
A hot topic
Low carbon steel containing between 12% and 14% chromium is highly resistant to carbon dioxide, hydrogen sulphide and the high temperatures (above 224 degrees C) found in deep oil and gas wells.
Following a boom in drilling for shale gas, the use of chromium steel tubing has soared over the last five years in the United States. Chromium compounds such as chromium lignosulfonate can be used in drilling fluids as deflocculants - compounds that reduce the fluid’s viscosity and prevent suspended rock material from clogging or corroding around the drill bit.
A new approach to materials
Predevelopment planning and a growing knowledge of corrosion control is benefitting newly discovered oil and gas fields. However, it still remains important to regularly monitor metal components for damage. Regular maintenance schedules are particularly advised in hostile environments where sea water or extreme temperatures could impact asset performance. With regular equipment checks, potential issues can be identified and dealt with before they become a high-cost, time intensive problem.
New technologies are being developed to improve monitoring techniques and reduce the likelihood of equipment failures. Condition based monitoring (CBM) is a maintenance strategy that monitors the condition of an asset to decide what maintenance needs to be done and when. CBM dictates that maintenance should only be performed when certain indicators show signs of decreasing performance or upcoming failure and will greatly minimise the cost and disruption of repairs. It is far easier to identify a problem early than to deal with an unexpected repair in the future.
The remote measurement and testing of equipment and pipelines can also help eliminate human risk. With continuous measurement, operators can discover leaks through a process called mass balancing. By accounting for material entering and leaving pipes, mass flows can be identified which might have been unknown, or previously difficult to measure. For example, operators can use mass balancing to identify corroded valves within their pipe systems that may be causing dangerous leaks. Remote action can be taken to update software, shut down failing or faulty systems, and if there is a danger of explosion, extract on-site personnel immediately.
The principles of corrosion need to be understood before selecting materials for oil and gas operations. Currently, 40% of all produced steel is used to replace corroded steel. Strong and resistant metals are the first line of defence against corrosion – safeguarding capital and industrial processes. The second line of defence is regular monitoring and maintenance of on-site equipment – identifying issues before they become a significant danger.
About the author
Martin Phillips is Product Manager at Fluenta, the supplier of ultrasonic flow measurement solutions for the Oil & Gas and Chemicals Industries. Formerly Product Manager at Nokia and Honeywell, Martin has worked in marketing and product management for more than 30 years, accruing international expertise in the full lifecycle development and launch of products across diverse market sectors.