Boiler condition could be a marketing tool

30 Nov 2013
boiler corrosion

Boiler corrosion in the absence of a passive magnetite layer

DNV is trying to encourage ship managers to take a new, more vigilant approach to boiler monitoring and maintenance, explains by Wendy Laursen

Over 25 vessels have been successfully assigned the DNV voluntary notation BMON since its inception 15 months ago. As well as being a tool reduce the frequency of defects related to corrosion and increase focus on inspection and maintenance regimes, particularly for auxiliary boilers, the notation is a signature to highlight high technical performance and safe boiler condition to the industry and charterers, says Tuva Flagstad Andersen, Head of Section at DNV-GL’s Machinery and Systems.

“We are seeing an increasing trend where ship managers are willing to accept conditions of Class (CoC) or memo to owners (MO) and operate their boilers with temporary repairs or acceptable but undesirable conditions respectively for an extended period of time,” says Ms Flagstad Andersen. “Some of the operators attempt to postpone remedial action, and we want to discourage this trend with this notation so that no observations adversely affecting the strength, safety and performance are acceptable in comparison to the boiler in the ‘as certified’ condition. Although we understand the commercial pressures the operators are subject to, the voluntary BMON notation has been developed so that we, as a classification society, can be pro-active rather than reactive about the risks of corrosion and oil contamination which are predominantly the most common root causes behind the defects and observations.”

BW Fleet Management AS (BW FM) based in Oslo has had the notation assigned to several vessels in their fleet. “We seek to maintain our boilers to the highest possible standards at all times” says Fleet Manager Olav Lyngstad. “Our LNG carriers trade in a demanding market and our customers expect the highest availability of our fleet. In order to plan maintenance in a systematic manner and reduce offhire, the BMON class notation has been a natural choice. It has helped us keep vessels in the market in periods when offhire would be expected”.

The BMON notation requires the boiler to be free of defects which may lead to Condition of Class (CoC) and MOs when the notation is assigned and during the boiler’s service life if the notation is to be retained. Additionally, boiler water testing on auxiliary boilers must be carried out every day rather than every second day, under BMON.

The BMON notation is also a huge benefit to ship managers because they no longer have to stop the ship for several days to open up the boiler for the surveyor in between their five year docking cycle. The first internal inspection in the class period is done by the chief engineer. They surveyor then reviews the documentation and if found in acceptable order carries out safety checks prior final acceptance of the survey. Needless to say, the evidence of satisfactory condition of the boiler, maintenance and inspection routines are subject to very strict scrutiny during periodic inspections.

The crediting of a boiler survey shall be carried out by a DNV surveyor within 45 days of the internal inspection undertaken and documented by the chief engineer. The scope of the survey will as a minimum include a review of the BMON record file/boiler water management records, an inspection of the fire side as deemed necessary and the testing of safety valves/monitoring systems as in a normal scope. Verification of the chief engineer’s formal qualifications also forms an integral part of the survey.

DNV handles a substantial number of boiler inspections and most of the issues they find that are related to steam and water side of pressure parts can be traced to the quality of the boiler water management on board. In a lesser number of instances, issues relate to mechanisms on the gas side, contamination by oil, safety/monitoring systems and, on rare occasions, the design.

Auxiliary boilers are the worst affected by problems linked to water management in conjunction with inherent limitations related to open feed systems, says Arun Sethumadhavan, senior engineer at the machinery and systems section in DNV-GL. “Closed feed systems, mechanical de-aeration, stringent water management and monitoring systems on propulsion boiler plants explain the logic behind this distinction quite well.”

Specific chemical treatment which assists the development and retention of a magnetite layer is mandatory for all boilers under BMON as it enables reduction of risks of corrosion by passivation. The development and retention of a passive magnetite layer is normally only possible with an extremely low dissolved oxygen content and a high boiler water pH (typically above 11). These conditions are highly unlikely to exist in auxiliary steam plants with open feed water systems without any provisions for mechanical evacuation of dissolved gases, especially oxygen.

The result of the enhanced BMON maintenance regime is a boiler in optimal condition allowing optimal heat transfer, lower fuel costs, fewer deficiencies, lower costs and less downtime, says Sethumadhavan. Higher hot well temperatures up to 95°C can be achieved to minimise the dissolved oxygen content, early warning of salt water or oil contamination is possible. Boilers in top condition, especially on vessels such as tankers that are subject to extremely strict safety inspections, can then become a point of differentiation with charterers, says Sethumadhavan.

“DNV is confident that the legacy introduced by the BMON notation will proactively manage the risks associated with the operation, monitoring and maintenance of steam plants. Customers who strive to maintain their boiler plants in an optimal condition will benefit from having the notation along with a concurrent branding of the boiler condition in the industry,” concludes Ms Flagstad Andersen.

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