Connect with us

Scrubbers

Outokumpu: Marine scrubbers sail ahead with specialist stainless steels

The conditions inside a scrubber are very harsh, with a combination of acids, elevated temperatures and a high chloride content in the wash water, explained corrosion specialist.

Admin

Published

on

Screen Shot 2020 11 04 at 1.25.24 PM

Global stainless-steel manufacturer Outokumpu on Wednesday (4 November) published an article explaining the mechanics behind why stainless steel is a more viable and cost-effective choice for the aggressive corrosion conditions found in marine scrubber units; it was written by Björn Helmersson, a corrosion specialist with Outokumpu:

In 2020, the International Maritime Organisation (IMO) introduced new standards intended to reduce sulfur emissions that cause acid rain and air pollution. Their main impact is that the sulfur content in the fuel oil used by merchant vessels is limited to 0.5% globally and 0.1 % in designated Emission Control Areas (ECAs) – the Baltic Sea area, the North Sea area, the United States, Canada, and the United States Caribbean Sea area.

Currently, vessel operators have two main options. They can switch to very low sulfur fuel oil (VLSFO) that contains less than the 0.5 % sulfur limit, but which is more expensive. Or they can install a scrubber that washes the vessel’s exhaust gases so that it can continue to run on high-sulfur fuel (HFO).

Scrubber designs

Generally, the shipping industry uses wet scrubbers (see Figure 1). These exhaust gas cleaning (EGC) systems wash the exhaust gas stream by forcing it into contact with water to remove the sulfur dioxide (SO2), a toxic gas that is directly harmful to human health.

There are three main design arrangements for marine EGCs:

  • Open-loop: This uses seawater to scrub the exhaust gas to remove SO2. The wash water is treated and discharged back to sea.
  • Closed-loop: Fresh water is used in a closed circuit that is treated with an alkaline chemical such as caustic soda.
  • Hybrid: This can be used in either open- or closed-loop mode according to operational needs.

Figure 1 – Open-Loop EGC system (credit: Exhaust Gas Cleaning Association).

Outokumpu figure 1

Material selection is critical for reliability

The conditions inside a scrubber are very harsh, with a combination of acids, elevated temperatures and a high chloride content in the wash water. To ensure the desired 20-year service life, high-alloyed stainless steels and nickel base alloys are required. It can be devastating to select a material with insufficient corrosion resistance. Yet the safest choice is seldom the most economic one.

Corrosion types and service conditions

There are three main types of corrosion risk found in marine scrubbers:

Pitting corrosion

  • Caused by a critical combination of chlorides, high temperatures and low pH
  • Stainless steel is protected against corrosion by a natural, self-forming passive oxide film on its surface. If a local breakdown of this protective film occurs it causes the formation of pits

Crevice corrosion

  • Caused by the critical combination of chlorides, high temperatures and low pH and the presence of crevices

Uniform corrosion

  • Typically occurs in very acidic conditions
  • Uniform corrosion rate across the surface

At the inlet, where the uncleaned gas meets the wash water, there is a mix of wet and dry conditions, with condensing acids from gas and chloride-rich wash water and elevated temperatures. These conditions are very aggressive with a risk of uniform and pitting corrosion.

Within the scrubber body there is a slightly acidic wash water combined with a lower temperature than the inlet. The main risk here is pitting corrosion. Similar conditions apply for other parts of the scrubber system, such as packing material, demisters, tubing and spray nozzles

Crevice corrosion may occur in areas where two surfaces are in close contact, such as flanges, packing material and under deposits.

The influence of scrubber type on material selection

In the open-loop design, the presence of chlorides typically requires the use of high-alloyed materials. In the closed-loop design, where water is recirculated and treated with caustic chemicals, the corrosivity depends on the quality of the wash water. Typically, the conditions are less aggressive than in the open-loop design.

Since the hybrid design alternates between open- and closed-loop operation, materials must be selected according to the most aggressive operating conditions. Therefore, the same materials are used as in an open-loop scrubber.

Operational experience and field testing are vital

Outokumpu has been supplying stainless steel for marine EGCs since 2006. It carries out extensive R&D activities including laboratory testing and long-term field testing in cooperation with marine scrubber OEMs and their customers. The results show that material selection must always be done on a case by case basis.

For the scrubber body, Ultra 254 SMO is one of the most widely used grades. This is a 6% molybdenum and nitrogen-alloyed austenitic stainless steel with extremely high resistance to both uniform and localized corrosion. It was developed initially for oil and gas offshore platforms and the pulp and paper industry.

However, in some cases it is possible to use a 25Cr super duplex stainless steel such as Forta SDX 2507. This offers similar corrosion resistance to Ultra 254 SMO and improved mechanical strength. It is well proven in extremely corrosive environments such as desalination, chemical, or offshore subsea applications.

Standard 22Cr duplex stainless steel can also be used successfully in less aggressive applications such as closed-loop designs and some parts of open-loop scrubbers. A typical example is Forta DX 2205, which is the most popular duplex product on the market. It offers very good resistance to uniform and localized corrosion in combination with high mechanical strength.

Ultra 654 SMO – an alternative for scrubber inlets

As the entry point for hot exhaust gas, the scrubber inlet is a particularly demanding application. Traditionally, Alloy 31 has been the material of choice. It is an iron-nickel-chromium-molybdenum alloy with nitrogen addition developed to fill the gap between special alloyed austenitic stainless steels and nickel alloys.

The test program has established that Ultra 654 SMO offers a viable and more cost-effective alternative. This is a 7% molybdenum and very high nitrogen-alloyed austenitic grade that is the most corrosion resistant stainless steel in the world.

Ultra 654 SMO has a higher mechanical strength than Alloy 31. If the design of the inlet enables this higher strength to be utilized then it could offer weight savings between 15 to 25%. Furthermore, the lower nickel content of Ultra 654 SMO also makes it cost-effective and more stable in price.

Practical examples

Outokumpu currently supplies stainless steel material for use in the construction of around 60% of the marine scrubbers installed every year. Two typical examples include:

Ecospray Technologies S.r.l. Italy (Figure 2) needed a highly corrosion resistant material for its exhaust gas cleaning scrubbers. Ultra 254 SMO proved to be the best combination of performance, price and dimensions.

Outokumpu figure 2

Figure 2 – Ecospray Technologies scrubber in Ultra 254 SMO.

ContiOcean Environment Tech Co., Ltd. delivers open-loop scrubbers to cargo ships of various size classes. Forta SDX 2507 provides the necessary corrosion resistance for the harsh conditions in the scrubber body (see Figure 3).

Outokumpu figure 3

Figure 1 – Open-loop marine scrubber manufactured by ContiOcean Environment Tech Co., Ltd in super duplex stainless steel

Summary – key facts about materials for marine scrubbers

  • Material selection is the most critical factor in helping ship owners to ensure the reliability of their exhaust gas cleaning (EGC) systems over a 20-year service life
  • A wide range of stainless steels can be used
  • Conditions and corrosivity vary depending on location and type of scrubber
  • Materials selection should always be made according to the specific operating conditions
  • Duplex grades can often replace the dominating austenitic choices
  • For the toughest situation found in the scrubber inlet Ultra 654 SMO offers a very competitive alternative to Alloy 31

 

Photo credit: Outokumpu
Published: 4 November, 2020

 

Continue Reading

ECA

VPS examines North-East Atlantic ECA on current bunker fuel mix and testing

Impact of this new ECA, will not only affect bunker fuel selection and testing, but it will also require a review of, voyage planning, bunker procurement and scrubber strategy, amongst others.

Admin

Published

on

By

RESIZED VPS logo

Steve Bee, Group Marketing and Strategic Projects Director, and Emilian Buksak, Decarbonisation Advisor of marine fuels testing company VPS, on Wednesday (8 April) highlighted MEPC 84 approved a new emission control area (ECA) covering the North-East Atlantic Ocean, with agreements reached on adopted amendments to MARPOL Annex VI. 

The new ECA, which will become the world’s largest emission control area, will be implemented on 1st September 2027

In a recent article, VPS outlined how VPS testing, data, CEM systems and advisory services can support vessels in both their operational and compliance challenges associated with this new ECA:

The recent International Maritime Organisation’s (IMO), Maritime Environmental Protection Committee (MEPC) meeting in London, had its main focus on setting binding greenhouse gas emission reduction targets for the global shipping sector. In keeping with the Committee’s continuing drive to decarbonise shipping and reduce the pollutant emissions from the global fleet, one major outcome from the MEPC-84 meeting was the approval of a new emission control area (ECA) covering the North East Atlantic Ocean, with agreements reached on adopted amendments to MARPOL Annex VI.

This new ECA, which will become the world’s largest emission control area, will be implemented on 1st September 2027, with the ECA requirements taking effect on 1st September 2028. It will cover the territorial seas and exclusive economic zones of Greenland, Iceland, the Faroe Islands, Ireland, the United Kingdom, France, Spain and Portugal, extending up to 200 nautical miles from their baselines:

VPS examines North-East Atlantic ECA impact on current bunker fuel mix and testing

A key advantage of the new NE Atlantic ECA is that it will close the gap between the existing ECAs in the North and Baltic Sea, plus the Mediterranean, creating an almost continuous zone of reduced shipping emissions. It will also connect to the newly approved ECAs in the Canadian Arctic and Norwegian Sea, which are scheduled for implementation in 2026 and 2027 respectively. Together these ECAs will cover almost half of all Arctic coastal waters, improving air quality, by reducing SOx, NOx and Particulate Matter (PM), protecting  public health, and reducing the environmental impacts from shipping.

The sulphur limit for the marine fuels allowed to be burnt within this new ECA will reduce from the current 0.50% to 0.10%. This will force vessels to use either effective abatement technology (scrubbers), or alternatively burn marine distillates, ultra-low-sulphur fuels (ULSFOs), or biofuels with a sulphur content of less than 0.10%.

Without doubt this new ECA will cause a significant change to the current fuel mix, probably on an even greater scale than was witnessed with the introduction of the Mediterranean ECA back in May 2025.  The fuel mix in the Mediterranean Pre-ECA implementation was,  53% VLSFO, 28% HSFO, 16% MGO, 2% ULSFO and 1% Biofuels. But from the 1st May 2025, the fuel mix changed to, 30% VLSFO, 29% HSFO, 30% MGO, 8% ULSFO and 4% Biofuels.  

So, in terms of actual tonnage, the Mediterranean ECA witnessed a decrease in VLSFOs by 23%, whilst MGO usage increased by 107%. At the same time, ULSFO and biofuels supply increased 4-fold.

Regarding fuel quality within the Mediterranean post-ECA implementation, MGO off-specification rates increased to 4%. However, the most worrying off-specification rates were for ULSFOs which saw a 10-times increase from 2% to 20% from the start of the ECA, with the main off-specification parameters being pour point, sulphur, TSP, CCAI, water and viscosity.

Therefore, it is fair to assume we’ll witness a similar dramatic fuel mix change upon the implementation of the NE Atlantic ECA, with possibly similar fuel off-specification issues, highlighting the continuing need for proactive fuel testing to protect vessels, crew and the environment.

Whilst the focus on fuel quality is essential, the multi-pollutant nature of this new ECA, covering SOx, PM and NOx, also brings the role of continuous emissions monitoring increasingly to the fore. Therefore, a further consideration relating to the impact of this new ECA relates to vessel newbuilds and the stricter NOx Tier III requirements. For newbuilds subject to the stricter NOx Tier III requirements, compliance depends not only on engine certification at delivery, but on demonstrating that exhaust after-treatment systems, typically Selective Catalytic Reduction (SCR) or Exhaust Gas Recirculation (EGR), continue to perform as designed throughout the service life of the vessel.

For scrubber-equipped ships, real-time SO₂ measurement provides the operational evidence of equivalency that Port State Control inspections increasingly expect to see. Plus, for vessels operating under multiple overlapping regulatory regimes, including the new NE Atlantic ECA, EU MRV, EU ETS and FuelEU Maritime, continuous emissions monitoring via the VPS EMSYS CEM system delivers a single, verified source of emissions data that can be applied across all of them.

As noted by DNV in their MEPC 84 technical and regulatory update, the newly adopted IMO measurement guidelines can also be used for determining actual methane and nitrous oxide under the EU ETS and FuelEU Maritime, confirming the direct route from IMO-recognised measurement to EU compliance reporting.

At an operational level, the new ECA will introduce considerable complexity in the way fuel consumption is attributed across voyage segments, with VLSFOs burnt outside the zone and compliant fuels inside, all of which carry implications for consumption reporting, charterparty allocation and EU MRV alignment. VPS Maress can provide the underlying fuel and energy data into one auditable platform, helping crews manage the operational complexity that the new ECA introduces, including voyage segmentation, fuel changeover and emissions accounting, plus providing the consolidated data foundation that feeds existing EU MRV and IMO DCS reporting obligations. 

VPS PortStats via the VPS Verisphere eco-system, (VeriSphere | VPS), further supports bunker procurement planning with port-by-port intelligence on compliant fuel availability and price spreads. Such intelligence and insights, will prove particularly valuable in the months immediately following 1st September 2028, when the supply pressure on 0.10% sulphur fuels is likely to peak.

Regarding the more strategic decisions ahead, including Tier III engine selection for newbuilds, retrofit feasibility for existing tonnage, and charterparty clauses allocating the ECA fuel cost premium between owners and charterers, VPS Advisory Services can provide the integrated commercial and technical perspective needed to navigate this transition with confidence.

Therefore, its clear the impact of this new ECA, will not only affect the choice of fuel to be burnt onboard and its subsequent quality testing, but it will also require a review of, voyage planning, bunker procurement, scrubber strategy, engine certification, compliance documentation and charterparty exposure.

Related: DNV on IMO MEPC 84: Revisiting Net‑Zero Framework

 

Photo credit: VPS
Published: 14 May, 2026

Continue Reading

Scrubbers

No open-loop EGCS with HSFO bunker fuel allowed in Saudi Arabian ports

Use of HSFO with an Open-Loop Exhaust Gas Cleaning System at 0.5% or 0.1% sulphur mode setting is prohibited until further notice for the ships entering Saudi Arabian ports, says GAC.

Admin

Published

on

By

Aramco: Ras Tanura Port, Eastern Province of Saudi Arabia, on the Arabian Gulf.

The use of High Sulphur Fuel Oil (HSFO) with an Open-Loop Exhaust Gas Cleaning System (EGCS) at 0.5% or 0.1% sulphur mode setting is prohibited until further notice for the ships entering Saudi Arabian ports, according to GAC Hot Port News on Wednesday (3 December). 

All ships entering Aramco ports shall comply with one of the following options:

  • Use compliant fuel oil (≤ 0.50% m/m Sulphur, or ≤ 0.10% when operating in ECAs, if applicable).
  • Operate the EGCS in Closed-Loop mode (or Hybrid system in Closed mode), with strict prohibition on the discharge of wash water into the sea.

 

Photo credit: Aramco
Published: 8 December, 2025

Continue Reading

Bunker Fuel

Equatorial navigates through sanctions and green transition amid shifting bunkering landscape

Shipowners’ demand for ‘cheapest compliant fuel’ suggests a potentially more competitive and shrinking market for LSFO, forecasts Choong Sheen Mao, COO at Equatorial.

Admin

Published

on

By

Equatorial navigates through sanctions and green transition amid shifting bunkering landscape

Singapore-based physical bunker supplier Equatorial Marine Fuel Management Services Pte Ltd (Equatorial) is adapting to a dynamic global bunker market shaped by regulatory shifts, geopolitical tensions, and the push for decarbonisation, states its Chief Operating Officer.

Choong Sheen Mao was amongst panellists of the Bunker Sellers Panel at IBIA Annual Convention 2025 in Hong Kong on Tuesday (18 November) when he shared a significant trend of shipowners increasingly opting for high sulphur fuel oil (HSFO) paired with scrubbers, driven by the pursuit of the “cheapest compliant fuel”.

Despite a narrowing spread between high and low sulphur fuels – from approximately USD 125 to USD 80, and occasionally below USD 70 – shipowners continue to see long-term investment returns from scrubbers. This shift suggests a potentially more competitive and shrinking market for low sulphur fuel oil (LSFO).

“Geopolitical instabilities, particularly armed conflicts, sanctions and trade wars, are creating considerable market distortions. These instabilities lead to supply disruptions, cargo rerouting, and impact bunker prices,” added Choong.

“Compliance has become a paramount concern, with recent substantial fines underscoring the risks involved. The current economic slowdown, compounded by sanctions and self-sanctioning, presents a ‘double pain’ for the market.

“The market’s daily volatility is also heavily influenced by global politics, making it challenging to assess without a deep understanding of geopolitical events.”

To ensure marine fuel quality, Equatorial emphasises managing its own supply chain and operating its own fleet of bunkering vessels, allowing for direct control from delivery to the customer, he stated.

This approach prioritises transparency and security, fostering long-term relationships where quality issues can be collaboratively addressed. Knowledge sharing, especially concerning parameters from new bunker fuel testing methods such as Gas Chromatography Mass Spectrometry (GC-MS), is also deemed crucial.

Supporting the transition to alternative marine fuels, while acknowledging the uncertainty surrounding the dominant future fuel, Equatorial has strategically invested in IMO Type 2 chemical tankers capable of handling methanol, biofuel, and conventional bunker fuels.

“Biofuel is identified as the most effective short-term solution, offering favourable pricing and operational costs compared to other green alternatives,” explained Choong.

“However, challenges include feedstock availability and potential export quotas from key producing nations like China.

“The adoption of alternative marine fuels necessitates a closer, more collaborative relationship between buyers and sellers.

“This involves detailed discussions on specific fuel specifications beyond standard ISO requirements, extensive lab sampling, and long-term commitments from both parties, particularly given the absence of a liquid hedging market for biofuels.

“Collaboration across safety, quality, and commercial aspects is essential for the successful implementation of bio bunker fuels to the future maritime market.”

 

Photo credit: International Bunker Industry Association
Published: 1 December, 2025

Continue Reading

Trending