ABSTRACT
New environmental regulations reduce the permissible level of sulfur emissions from ocean vessels. Frequently, the most economical means of meeting the regulations is through the use of a diesel exhaust scrubber. The scrubber environment includes chlorides, high temperatures, and acidic conditions and requires the use of corrosion resistant alloys. This study compares multiple alloys in several simulated scrubber environments. The alloys tested include a common austenitic alloy - UNS S31603, four superaustenitic alloys - N08367 (6 wt. % Mo), N08367 (7 wt. % Mo), N08830 and N08031, three Ni-Cr-Mo alloys – N06625, N10276, N06059, and two titanium alloys - Grade 2, UNS R50400 and Grade 38, R54250. These comparisons are essential for proper material selection as the demand for marine exhaust scrubbers grows to meet the new regulations.
INTRODUCTION
Due to new environmental regulations, substantial growth is expected for marine diesel exhaust scrubbers. Regulations limiting allowable sulfur emissions from ships burning heavy fuel oil (HFO) in certain regions, referred to as Emission Control Areas (ECA's), are requiring significant changes to marine vessel exhaust. The ECA's established under MARPOL (International Convention for the Prevention of Pollution from Ships) Annex VI for sulfur oxides (SOx) are: the Baltic Sea area, the North Sea area, the North American area (covering designated coastal areas off the United States and Canada) and the United States Caribbean Sea area (around Puerto Rico and the United States Virgin Islands)1. In addition, future regulations are expected to cover a larger area. Outside the emission control areas, the current limit for sulfur content of fuel oil is 3.50 wt. %, tentatively scheduled to fall to 0.50 wt. % in 2020. The 2020 date is subject to a review of the availability of the low-sulfur fuel oil. Depending on the outcome of the review, which is expected to be completed by 2018, this date could be deferred to 20251. Available options to meet the regulations are to burn more expensive low sulfur fuel, switch to natural gas, or install an exhaust scrubber system. Because the scrubber option is not subject to fuel price fluctuations, it is becoming a preferred choice for the marine vessel industry.
