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Duplex storage tanks
29/05/2018
Duplex stainless steel storage tanks are an increasingly popular choice for tank owners, not just for their long, low-maintenance service lives, but also because they can actually reduce initial costs for tank owners. The higher strength of duplex grades permits thinner tank walls, requiring less steel, and because additional coatings or treatments are not required, duplex tanks can compete on installed cost with carbon steel tanks.
Photo credit: © Börger GmbH
Carbon steel storage tanks tend to dominate in chemical and petrochemical storage because such products are not generally very corrosive, although corrosion from moisture and the external environment must still be considered, requiring the use of coatings or cathodic protection.
Austenitic stainless steel (Type 304 or Type 316) can be used an alternative, but these options tend to be more expensive because their lower strength means that thicker walls (and more steel) are required.
Thanks to their higher strength, duplex stainless steel tanks can be less expensive to build than either austenitic or carbon steel tanks, a cost advantage which is even more pronounced once whole lifecycle costs are considered. Tank designers most often specify lean duplex stainless steels containing 0.3%-0.5% molybdenum, with higher-molybdenum grades specified for more corrosive environments.
Aside from lower construction costs, operating costs for duplex stainless steel tanks are significantly lower than those for carbon steel tanks, as their good corrosion resistance means very little maintenance over a virtually limitless life.
Duplex tanks are easily cleaned and are ideal for a wide variety of substances, making them much more operationally versatile than carbon steel tanks. If and when they are taken out of service, scrap values are much higher and the stainless steel can be profitably recycled. Many of these sustainability advantages are due in large part to the presence of molybdenum.
This post is adapted from an original article in MolyReview, in which we showcase some of the most interesting and amazing uses of molybdenum. Jump straight to the full version of this article here.
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