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Underwater repair specialist Hydrex has noted an increase in work on pipes and overboard outlets of ships that have had exhaust gas cleaning systems (or ‘scrubbers’) fitted.

Scrubbers remove sulphur oxide compounds from exhaust gasses of marine diesel engines burning high-sulphur heavy fuel oils, enabling ships to meet current and future sulphur emission regulations. However, the residue can have a rapid, corrosive effect on scrubbers’ internal pipework and outlets.

“We have noted an increase in repairs to corroded pipework and outlets which does appear to correspond with the increase in the number of ships fitted with scrubbers,” confirmed Dave Bleyenberg, production executive, Hydrex. (read more)

Among recent cases, Hydrex diver technicians carried out pipe replacements on two 276m shuttle tankers. Wash water from the scrubbed exhaust gases had corroded pipework. Repairs to the tankers were carried out while the vessels were alongside and remaining in operation. After the success of a repair on one vessel berthed in Rotterdam, Hydrex was contracted to carry out the same operation on the sister ship berthed at Skagen in Denmark, which had experienced the same problem.

“With the first tanker, working space was limited,” said Bleyenberg. “Several of the frames around the pipe had to be removed before technicians could cut away the corroded part of the old pipe. While the shell plating was prepared for the installation of the replacement pipe, a new diffuser and flange were fabricated on site. The replacement pipe was then positioned and secured with a full penetration weld, and the new diffuser installed.”

For protection against further corrosion, the internal surface was coated using Ecospeed, a chemical-resistant coating from Hydrex sister company Subsea Industries.

Scrubber installations are projected to increase as ship owners look for cost effective ways to comply with the IMO’s 2020 sulphur cap. Use of scrubbers enables ships to comply while still burning cost-competitive high-sulphur fuel oil.

Ecospeed is an abrasive protective coating that can be used on the hull or for other solutions.

Ecospeed is used by several shipowners and it is one of the few coastings that can be used in Arctic seas. There is a risk that conventional anti-foulings can degrade rapidly in polar ice, leach chemicals or leave paint fragments behind when ice impacts damage the coating. There is no such risk with a hard-type coating. Ecospeed is a tough, durable and highly abrasion resistant protective coating.

Acidic wash water from scrubber treatments is causing an increase in corrosion-related pipe repair. Photo: Hydrex-Subsea Industr