The oil and gas sector supplies more than 70% of the UK’s total primary energy and contributes £24 billion in gross value added to the economy, according to Oil & Gas UK. However, what once appeared to be a buoyant and watertight sector is now starting to spring a few leaks, including a rising cost base, declining resources, the impact of the steep drop in prices, and a burdensome fiscal regime.
So the industry has increasingly needed to focus on innovation and cost efficiency, particularly when trying to get the most out of ageing offshore infrastructure. One area that is playing an important role in keeping the industry afloat is materials research. In recognition of the “critical dependence of the energy sector” on new materials, the International Centre for Advanced Materials was set up by BP with a $100 million investment in autumn 2012, to be spent over a 10-year period.
Dr Bob Sorrell, ICAM associate director, says: “The industry is moving to ever more demanding environments to meet the world’s energy needs. This brings with it greater challenges of pressure, and reservoir temperatures of up to 375°F. Research in the BP-ICAM is helping us to understand the fundamental science and extend the operating range of carbon steel as well as develop new materials for these challenging environments.”
Set up to access and develop the skills of young researchers, the centre brings together the expertise of the universities of Manchester and Cambridge, Imperial College London, and the University of Illinois at Urbana-Champaign.
Extending asset life
ICAM has a diverse range of projects investigating coatings that can help materials to self-heal, says Sorrell. “For materials that are exposed to demanding environments, the ability to self-heal has many benefits – for example, reducing operational downtime and extended asset life.”
Imperial College has been developing a molecular-scale understanding of membrane structure and transport to explain and predict the performance of materials used for reverse osmosis and nano-filtration processes. This research will have “significant implications for membrane operating efficiency” for the industry, says Sorrell.
One significant focus at ICAM has been on developing types of steel that not only have greater mechanical strength but also resist corrosion at higher temperatures and pressures, as the industry taps into deeper basins and more remote areas of the earth. Despite corrosion incurring global annual costs of more than $2 trillion, its processes are still poorly understood.
Professor Philip Withers, ICAM director at the University of Manchester, says: “We do not know why corrosion occurs in one part of a steel pipe, but at a nearby location there is no corrosion. Nominally it is the same material. By understanding why at a microscopic level, we can start to develop new anti-corrosion materials that could minimise, or prevent, the process. To study the process taking place, we need to take a journey, travelling down the different scales and understanding each process as we go.”
ICAM uses a wide range of instruments for multi-scale imaging – including X-rays and microscopes – which allow researchers not only to observe a crack in a flange, for example, but also to determine the origins of the crack at the atomic level. This approach will lead to a better understanding of the bulk materials properties, such as interrelating structure, function and performance. Computer models are also used to understand how molecules interact and behave, helping the researchers to make “informed choices and minimise iterative experimental processes”.
Inspecting the damage
The first stage of examining the corrosion process uses surface-imaging techniques to focus down 1,000 times to the millimetre scale. This process has led to a greater understanding of corrosion taking place across the surface of materials, but corrosion also occurs at a sub-millimetre level, where it is referred to as localised corrosion. This localised corrosion is deemed more insidious, and can lead to other damage processes, such as pits in the metal or cracking.
To view corrosion at this level, ICAM uses electrochemical scanning techniques, running a probe across the surface to monitor selected sites. The activity seen results from metal dissolution at predetermined sites, at inclusion or grain boundaries, causing pH and cathodic reactions that create acidic conditions that can lead to corrosion.
Using X-ray computed tomography, researchers can move 100 times closer to analyse the material at the 10µm scale. This process is non-destructive, and allows them to image and visualise the nucleation of local corrosion sites to gain greater insights into types of corrosion, including metal pitting, and into different corrosion mechanisms. They achieve the image by using the X-ray to take multiple 2D radiographs of a sample at various angles, which are later used to create a computer-generated 3D image of the sample. These steps can be taken out over different periods (4D imaging) to observe different stages of corrosion or cracking in materials.
To look at these images in even higher resolution, at the 100nm scale, the researchers use focused ion beam scanning electron microscopes. Dr Ali Gholinia, research fellow at the University of Manchester, says: “This enables the researchers to look at the grain boundaries in the microstructure which are involved in corrosion activity.”
To achieve a good image, a focused ion beam is used to eject single atoms from the sample surface and cut the sample in successive nm slices, which are again later compiled to create a 3D reconstruction. In being able to see single atoms and analyse nanoscale regions of material using the electron microscope, the researchers can see the grain boundary that is ahead of the proceeding corrosion path. They can also see either side of that grain boundary, understand how the atomic structure on either side determines its structure, and analyse – at a very local nano scale – the kinds of elements that might be segregated or depleted along that boundary.
This knowledge then enables the researchers to design new materials. This process is under way at the University of Cambridge, where research teams are using computer-aided modelling to design corrosion-resistant steels that can trap harmful elements and render them harmless. Withers says: “A key aspect in the designs of these materials is to ensure they are manufacturable and will have an assured life. These components will work at high pressures and temperatures for long periods, and we have to make sure they are fit for purpose.”
ICAM research teams are confident of further breakthroughs. “One promising area is understanding the relationship between a solid or a liquid and its interaction at a surface,” says Sorrell. “Understanding this relationship will help develop insights into how deposits form in a range of environments, from our upstream and downstream operations to car engines. It will enable us to further inhibit deposits being formed – for example, through advanced automotive lubricant formulations.”
Did you know? Corrosion in steel
Two of the primary reagents leading to internal corrosion in steel oilfield equipment are carbon dioxide (CO2) and hydrogen sulphide (H2S). Both dissolve in water, forming acidic solutions that stimulate corrosion through cathodic (evolution of H2) or anodic (dissolution of iron) processes.