Super duplex in carbon capture storage plants

Super duplex in carbon capture storage plants Super duplex in carbon capture storage plants FEATURED STORY

Global leaders are trying to regain momentum on climate change to pivot from negotiating to implementing the massive transformations required. The effort involves legislation, policies and programs, as well as cooperation and support for implementation in four priority areas: mitigation, adaptation, loss and damage, and finance.

By Srikumar Chakraborty, ex ASP/SAIL, Member of Freelance Consulting Team

The effects of climate change due to the impact of greenhouse gas (GHG) emissions are being felt across the globe. The message that GHG emissions must be cut is unambiguous and internationally accepted. The climate crisis calls for the rapid transformation of society, yet it seems that the international community is falling far short of the Paris Accord goals, with no credible pathway to the 1.5°C maximum temperature increase goal in place. Only an urgent system-wide transformation can avoid climate disaster. Japan, Korea, Canada, and New Zealand have passed laws committing to achieving net zero emissions by 2050, while Ireland, Chile and Fiji have proposed legislation.

Super duplex in carbon capture storage plants
Figure 1. The carbon capture and storage process. Image: Global CCS Institute

The UK has a legally binding net zero target by 2050 and new interim targets to reduce emissions by 78% by 2035. It is essential to build a truly global coalition to achieve carbon neutrality by 2050.

The European Union has committed to doing so; the UK, Japan, the Republic of Korea and more than 110 countries have done the same. So, too, has the United States administration. China has pledged to get there before 2060.

Every country, city, financial institution and company should adopt plans for net zero – and act now to get on track for that goal, which means cutting global emissions by 45 per cent by 2030 compared with 2010 levels.

Development of CCS technology

The process of carbon capture and storage (CCS) involves capturing man-made carbon dioxide at its source and storing it permanently underground (Figure 1). This process consists of three main steps:

  • capturing and separating CO2 from other gaseous products from combustion,
  • compressing and transporting the captured CO2 to the sequestration location,
  • inserting the carbon dioxide into subsurface geological reservoirs.

CCS technology prevents the escape of GHG into the atmosphere by sequestering. Many CCS processes involve low temperatures combined with the presence of water, which originates during the combustion of gases. The presence of water can result in acidic conditions with a subsequent risk of corrosion.

As such, carbon or low alloy steel parts or components are unsuitable. Stainless steel and higher grade nickel-, chromium- and molybdenum-added stainless steels are the most suitable material for effective and safe operations and a better lifecycle.

Risks in the industry

One major concern with CCS is the leakage of CO2 from the pipes in underground reservoirs due to corrosion, with the resulting leakage contributing to climate change, or tainting nearby water supplies. There is also a risk of human-made tremors which may develop from the build-up of pressure underground, known as induced seismicity.

Overcoming such situations through preventive maintenance of equipment and part replacement is too costly. It can only be avoided through the use of duplex or super duplex stainless steel for pump and pipe connections. Furthermore, shutdowns to carry out maintenance work may create other, associated problems. CCS technologies are helping European countries and the USA to fulfil their challenging domestic climate goals by enabling the abatement of difficult-to-electrify industrial processes, low-carbon dispatchable power generation, and delivering the physical and market infrastructures necessary for many carbon dioxide removal (CDR) concepts.

Super duplex in carbon capture storage plants
Table 1. Super duplex stainless steel pumps used in a Carbon Capture Storage Unit

Role of super duplex

In the stainless steel family, super duplex stainless steel has a microstructure comprising an approximately 50:50 mixture of austenite and delta-ferrite. It is designed to provide improved corrosion resistance, particularly for chloride stress corrosion and chloride pitting corrosion. Super duplex also achieves higher strength than standard austenitic stainless steel types 304 and 316.

Metallurgical explanation

There are several key differences between super duplex stainless steels and duplex stainless steels. Super duplexes are based around an alloying addition of 25% Cr, whereas duplex stainless steels are based around an addition of 22% Cr. With the increased Cr content, the level of pitting corrosion resistance is increased. However, there are other variables.

Super duplex in carbon capture storage plants
Table 1. Composition & important properties of super duplex

Duplex stainless steel received its name because its metallurgical structure consists of two dual phases – austenitic (FCC – face-covered cubic lattice) and ferrite (BCC- body-centered cubic lattice).

Super duplex stainless steels have Cr in the range of 20% to 28%, i.e. a higher Cr content, up to a 5% Mo content, 9% lower nickel, and only 0.05 – 0.5% nitrogen. The Pitting Resistance Equivalent Number (PREN) is calculated as PREN = %Cr + 3.3x %Mo + 16x %N.

By increasing the Cr content, the PREN increases from 34 to >40, indicating a superior resistance to pitting corrosion over a broad range of environments. Super duplex grades are the default choice for subsea and marine applications due to their recognised long life.

By increasing the chromium content, the level of pitting corrosion resistance is also increased. The possibility to use thinner sections provides significant cost benefits for industries such as offshore oil and gas for piping systems, manifolds, and risers; and in the petrochemical industry for pipelines and pressure vessels.

Expected total benefits

Carbon capture and storage is a set of technologies that can help to meet ambitious domestic climate goals, enabling low-carbon dispatchable power generation while delivering the necessary physical and market infrastructures. However as it is a costly process involving high capital costs, there is a real threat of under-utilisation of the technology.

Achieving 2050 net-zero targets will almost certainly rely on this technology or other developed technologies being studied by many developed and developing countries. CCS provides a near-term pathway to rapidly reduce the impacts of existing emissions-intensive industries.

Super duplex in carbon capture storage plants
Figure 2. CO2 storage overview. Image: Global CCS Institute


The most challenging problem for carbon capture, storage and transportation technology is the collection of mixed flue gases and then removing contaminants such as sulfur, nitrogen oxides, fluorides and chlorides to obtain relatively pure CO2 which can be easily transported and stored. The most common techniques for carbon capture involve extracting carbon dioxide from either flue gases from the combustion of fossil fuels or biomass, or where CO2 is a byproduct of the conversion of those raw materials to other products.

While renewable and nuclear power generation plays a significant role in lowering carbon emissions, power generation with fossil fuels tends to respond to changes in electricity demand more quickly. This is why industry professionals are seeking a more conservative option that both lowers emissions and maximises power output. However, the basic idea involves the transportation of CO2 from coal- and gas-fired power plants via pipelines or other means to be injected deep into the ground (Figure 2). Engineers and metallurgists are working together to find ways of cost-effectively removing the various contaminants using environmentally friendly methods.


COP27, Metal Hand Book, Progress in Technology Development., Corrosion Hand Book.

About this Featured Story

This Featured Story appeared in Stainless Steel World May 2023 magazine. To read many more articles like these on an (almost) monthly basis, subscribe to our magazine (available in print and digital format – SUBSCRIPTIONS TO OUR DIGITAL VERSION ARE NOW FREE.

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