Corrosion countermeasures for LNG storage tanks made of series 5083 aluminum–magnesium alloy

Abstract

Natural gas as produced contains various kinds of gaseous hydrocarbons and nitrogen and is purified to ensure safe storage and use. Finally, the gas is cooled to below −162 °C to liquefy it, resulting in purified LNG, because it is non‐corrosive. Independent prismatic storage tanks are made of thick plates of the 5083‐series aluminum–magnesium (Al–4Mg) alloy that is grouped with corrosion‐resistant aluminum alloys. The tanks are covered in insulation and stored in a ship hull, which means the aluminum alloy LNG storage tanks are not prone to corrosion while in use. The tanks are to be used not only for storing LNG, but also as floating storage tanks and offloading units at offshore bases. When the Al–4Mg alloy is to be utilized to construct a large LNG storage tank, numerous alloy sheets are required. Here, one recommended method for storing the alloy sheets involves using resin board spacers of insulating plastic materials to avoid any undesired modification of the alloy sheet surfaces during storage. The inner surface of the tank thus constructed is temporarily exposed to corrosive conditions, of the type encountered when conducting water‐filling hydraulic tests to assess the structural integrity of the tank constructed. The water used for the water‐filling hydraulic test contains very few corrosive chemicals or precipitation substances and the surface should be kept dry once the water‐filling hydraulic test is complete. Copyright © 2015 John Wiley & Sons, Ltd.