Wärtsilä and Maersk To Develop Corrosion Mitigation Strategy

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Wärtsilä and Maersk have joined in an attempt to prevent ’severe corrosion’ from scrubber washwater causing damage to pipes and vessel hulls, reports Riviera.

Corrosion

According to Wärtsilä and Maersk, the acidity of scubber washwater discharged out of pipes directly into the ocean from the open-loop scrubber configurations that make up the majority of the estimated 5,000 scrubber systems installed on the global shipping fleet has a “particularly high” chance of corroding “mild steel”.

“Under IMO Guidelines, the washwater from exhaust gas cleaning systems, commonly referred to as scrubbers, should have a pH of no less than 6.5. However, in reality the pH of scrubber washwater is typically acidic, prior to being diluted by seawater. This creates the risk of structural corrosion to the discharge pipes,” the companies said in a joint statement.

“The risk is particularly high for pipes made of mild steel. In some cases, if the discharge pipes are inadequately protected, severe corrosion can damage the surrounding mild steel hull plates, resulting in water ingress.”

Solution for the problem

The fix for the problem of scrubber washwater eating away steel pipes and potentially rendering ships’ hulls vulnerable to taking on water, according to the two companies, is adding two more layers, or sleeves, as a retrofit to existing, and potentially corroded washwater discharge pipes.

“The new ‘pipe-in-pipe’ solution allows for the original overboard pipe to remain in situ while a new glass reinforced epoxy (GRE) pipe is inserted into it. No metal cutting or welding is necessary. An SMO steel sleeve is inserted between the new GRE pipe and the existing steel pipe. An adhesive permanently secures the GRE pipe in place. Since this ‘pipe-in-pipe’ solution has a small impact on the internal diameter of the pipe, it is best suited for overboard pipes with a diameter greater than 300 mm,” the joint statement said.

The companies are marketing the extra piping as a “long-term solution” for use at any time “even if corrosion has not yet occured”. Pipes can be delivered and kept on board or safely stowed at one of the companies’ facilities, awaiting a fitting during a vessel’s scheduled drydocking or port call. The companies said they can install the pipes while vessels are in operation, if required. In “most cases”, the companies said, the repairs will be finished in under two days’ time.

“We have noted corrosion incidents occurring on some scrubber-equipped vessels and wanted to be proactive in solving the problem,” Maersk senior lead specialist Jorn Kahle said.

“Additionally, taking a vessel out of service is extremely costly. One of the key driving forces for development of this pipe-in-pipe concept with Wärtsilä Underwater Services is to minimise these disruptions and costs. We are happy to offer this unique cost-efficient service to any vessel with any make of scrubber.” 

An increasing number of ports are limiting scrubber use over worries of threats to marine environments from washwater discharge. These ports are taking a cautious approach, choosing to ban the use of the open-loop scrubber configuration in ports and coastal waters – often fragile and already environmentally stressed ecosystems – out of fear of further damage to coastal marine life.

MPEC

The European Commission, with member states, has submitted a paper (MEPC 74/14/1), Proposal for evaluation and developing harmonised rules and guidance on the discharge of liquid effluents from exhaust gas cleaning systems, to the Marine Environment Protection Committee (MEPC).

The paper suggests “present knowledge on the composition and harmfulness to the marine environment of liquid effluents discharged by the majority of these systems into ports and sensitive sea areas lead states to take local or regional restrictions or prohibition measures.”

The paper specifies it is a matter of urgency (within the span of two MEPC sessions) to introduce the harmonisation process – the key objective being, “It is considered necessary to take appropriate regulatory measures, taking into account scientific knowledge, to protect certain areas from pollution resulting from the mentioned discharges, which could also include discharge bans from ships using a specific technology.”

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Source: Riviera

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