WSS highlights value of boiler treatment
Oxygen corrosion is the most common corrosion problem seen in boilers, and Wilhemsen Ship Service (WSS) believes it has found a solution.
W
hile dissolved oxygen contained in all natural water is a necessity for all marine life, it will create
problems in a boiler. Oxygen will react with the steel and produce iron oxide – most commonly known as rust. If not controlled this may eventually lead to the failure of the boiler. The level of dissolved oxygen is about
8ppm at room temperature. It decreases with increasing temperature and is around 5ppm at 60°C, 3ppm at 80°C and approaches 0 at the boiling point of water. Hence, applying as high a temperature as possible in the hotwell is important and will decrease the amount of oxygen to be removed by a chemical oxygen scavenger. Sodium sulphite is one of the oldest and most proven oxygen scavengers available.
It reacts quickly with oxygen even at low temperatures to form sodium sulphate, a non-toxic, neutral salt that is non-corrosive to the boiler. In practice, approximately 10ppm sodium sulphite is required to react with 1ppm of oxygen. WSS is recommending the use of
Liquitreat, a multifunctional boiler water conditioner suitable for boilers with a pressure up to 30bars. It contains alkalinity control, phosphate as a scale inhibitor, sodium sulphite as an oxygen scavenger, and sludge control. In 2009, WSS reports that it successfully treated more than 4000 vessels with Liquitreat. According to Steinar van der Meer, R&D
manager at the WSS subsidiary, Unitor Chemicals: “Liquitreat should preferably be continuously dosed into the feed water line
or in the hotwell to protect the feed water system from oxygen corrosion. Slug dosing is not recommended because oxygen will continuously enter with the feed water and needs continuous removal. If alkalinity is high, dosage should not be discontinued; instead the blowdown of the boiler should be increased.” The design and layout of feed water
pumps may prohibit the use of higher temperatures in the hotwell due to cavitation and/or gasket leaks. Replacing the pumps at lower decks and replacing pump seals may be possible mitigations. WSS says it strongly recommends the
use of Condensate Control in conjunction with Liquitreat. T is is a volatile amine that neutralises carbonic acid in the condensate return. SRCT
Integrated System Solutions Electrical Systems for Newbuilding and Retrofit
SAM Electronics GmbH Behringstrasse 120 22763 Hamburg . Germany
Phone: +49 - (0)40 - 88 25 - 21 21 Fax:
+49 - (0)40 - 88 25 - 41 00
ISS@sam-electronics.de www.sam-electronics.de
Shiprepair and Conversion Technology 3rd Quarter 2010
Please visit us at SMM Hamburg, 7-10 September 2010, Hall B6, Stand 340.
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