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Effects of Alloying Elements for Resistance to Naphthenic Acid Corrosion of 18Cr Austenitic Stainless Steels

In this study, the effect of Mo, Cu and W contents in stainless steels on both NAC and PTA SCC resistance are investigated. The purpose was to optimize a proprietary version of UNS S34751 (TP347LN) with excellent PTA SCC resistance.

Product Number: 51317--9057-SG
ISBN: 9057 2017 CP
Author: Masahiro Seto
Publication Date: 2017
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$20.00
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Naphthenic acid corrosion is suffered in chemical plants at an atmospheric distillation unit vacuum distillation unit and their surrounding equipments such as transfer lines and side cut pipes. The refineries for high TAN (Total acid number) crude cause the naphthenic acid corrosion of carbon steels or low alloy steels.In addition naphthenic acid corrosion will be inevitable due to increasing of high TAN crude refineries by state-of-art crude refining technologies.Conventional austenitic stainless steels as 316L and 317L containing high molybdenum content are effective for naphthenic acid corrosion compare with carbon or low alloy steels. However amounts of molybdenum of them are limited because of harmful influences on their metallurgical stability formability weldability and fablicability etc. In this paper the effective elements such as molybdenum for resistance to the naphthenic acid corrosion are precisely conducted. At the results of the naphthenic acid corrosion tests nickel is proved to be effective in naphthenic acid corrosion because of the formation of nickel sulfide film as well as that of molybdenum sulfide film. On the other hand tungsten and cupper are found to be ineffective compared with molybdenum.At the conclusion three kinds of corrosion mechanism are classified according to the amounts of effective elements molybdenum and nickel. In the case of sufficient amounts of effective elements; molybdenum with more than 3% and nickel with more than 14% respectively naphthenic acid corrosion is perfectly prevented. In other cases pitting corrosion and/or aggressive corrosion are inevitable.

Key words: Naphthenic acid corrosion, Polythionic acid stress corrosion cracking, Molybdenum, Copper, Tungsten, 18Cr Austenitic stainless steel, 317L, 347LN

 

Naphthenic acid corrosion is suffered in chemical plants at an atmospheric distillation unit vacuum distillation unit and their surrounding equipments such as transfer lines and side cut pipes. The refineries for high TAN (Total acid number) crude cause the naphthenic acid corrosion of carbon steels or low alloy steels.In addition naphthenic acid corrosion will be inevitable due to increasing of high TAN crude refineries by state-of-art crude refining technologies.Conventional austenitic stainless steels as 316L and 317L containing high molybdenum content are effective for naphthenic acid corrosion compare with carbon or low alloy steels. However amounts of molybdenum of them are limited because of harmful influences on their metallurgical stability formability weldability and fablicability etc. In this paper the effective elements such as molybdenum for resistance to the naphthenic acid corrosion are precisely conducted. At the results of the naphthenic acid corrosion tests nickel is proved to be effective in naphthenic acid corrosion because of the formation of nickel sulfide film as well as that of molybdenum sulfide film. On the other hand tungsten and cupper are found to be ineffective compared with molybdenum.At the conclusion three kinds of corrosion mechanism are classified according to the amounts of effective elements molybdenum and nickel. In the case of sufficient amounts of effective elements; molybdenum with more than 3% and nickel with more than 14% respectively naphthenic acid corrosion is perfectly prevented. In other cases pitting corrosion and/or aggressive corrosion are inevitable.

Key words: Naphthenic acid corrosion, Polythionic acid stress corrosion cracking, Molybdenum, Copper, Tungsten, 18Cr Austenitic stainless steel, 317L, 347LN

 

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