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Exotic Materials

Exotic Materials

Exotic Materials

Just a question because I know it is coming, What is API's stance on using an AL-6XN or 254 SMO material on a tank. I know Duplex is now widely accepted in harsh environments. If these materials are requested can the parameters in Annex X be used with them? Or will it just be per good engineering practice? Also can a tank have an API name plate with these materials?

RE: Exotic Materials

Duplex and Super duplex stainless steels are recent additions in API-650 Code. Not sure when they were included, however these alloys are in Annex-X of API-650.One important criteria for selection of these alloys(Duplex Stainless Steel) are the high Yield and UTS, which definitely adds to savings in tankage foundation cost. 254 SMO definitely falls behind with respect to above(strength) properties, although it outweighs some grades of duplex stainless with respect to CPT and CCT.

My understanding is that higher CPT and CCT may be a criteria for some storage media, which may be well taken care of by SDSS also.

The illustration on page 1 of the following article explains the differences between various alloys quite well for storage tanks..


Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist

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