ABSTRACT

New environmental regulations have substantially reduced the permissible level of sulfur oxide emissions from ocean vessels. An 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 will build upon a previous study that compared the corrosion resistance of multiple corrosion resistant alloys in several simulated scrubber environments. The current study evaluates the effect of welding and the presence of a crevice on five alloys. The alloys include a common austenitic alloy, UNS S31603; two superaustenitic alloys, N08367 and N08031; and two Ni-Cr-Mo alloys, N10276 and N06059. 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. The new regulations limit the allowable sulfur content in heavy fuel oil (HFO). Marine vessels use HFO as the primary fuel. Current regulations are in effect in certain regions, referred to as Emission Control Areas (ECAs). The ECAs established under MARPOL (International Convention for the Prevention of Pollution from Ships) Annex VI for sulfur oxides 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. The sulfur content in HFO in the ECAs is limited at 0.10%. In 2020, new regulations will be applied globally. Currently, outside the emission control areas, the limit for sulfur content of fuel oil is 3.50 wt.%. However, it is scheduled to be reduced to 0.50 wt.% in 2020. 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. Therefore, understanding the corrosion behavior of available materials for reliable scrubber design is of increasing importance.

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