The global Sulphur Cap is in force now and many owners have opted for Exhaust Gas Cleaning Systems (“SOx scrubbers”) to achieve compliance. DNV GL conducted a study to learn about the challenges in scrubber operations and how to overcome them.

First of all, DNV GL indicates there is currently a four- to five-month backlog of vessels that should have been retrofitted by the end of last year. Dr Fabian Kock, Head of Environmental Certification at DNV GL – Maritime, expects ‘it will probably take until April or May to complete all scrubber installations.’

The delays are caused by material shortages and limited yard capacity. ‘For example, there is only a limited number of manufacturers of GRE pipes in China where most scrubbers are installed,’ says Kock. ‘Designers and yards have a high workload of retrofit installations, and lack of staff has doubled the installation time at yards from forty to eighty days.’


Yet, the coronavirus also plays a role. ‘Workers may be unavailable at some Chinese repair yards,’ explains Kock. ‘The epidemic is also affecting sea trail attendance and travel restrictions have been put in place in some jurisdictions.’

Leakage, corrosion and sensor failures

The main challenges according to the study carried out by the classification society are leakage and corrosion of SOx scrubber overboard pipes. Kock: ‘To account for that risk, DNV GL has updated its rules and requires annual thickness measurements on various overboard pipes and spool piece designs.’

Another problem are sensor failures. ‘When a sensor fails, the control system can get the wrong data and cause an incorrect or unnecessary operational response,’ explains Kock. ‘Misleading sensor data can also falsely suggest that emissions are within limits and only when the emissions are checked by an authority will this be detected. In that case, the operator may get a penalty in the form of a high fine; in some ports the responsible officer might even be arrested.’

Best practices

To avoid or overcome these challenges, DNV GL advises to adhere to the planned maintenance intervals and to conclude a service agreement with the sensor manufacturer. ‘Keeping spare parts on board is also vital to avoid prolonged scrubber outages,’ adds Kock. ‘Furthermore, a preliminary test of the control system can help avoid failure during operation as well as costly repairs or reinstallations.’

Picture (top) by Roberto Venturini. Picture of Fabian Kock by DNV GL.