Naphthenic Acid corrosion in Duplex SS

[Peter113]

hI,
for a pump operating wiht naphthenic acid content > 2% (atmospheric residue pump) and 339ºC, the proposed material for shaft is Duplex SS (UNS 32205). I know the resistante for such organic acids depends on the alloy content. For high naphthenic acid content-high turbulence and high temperature, % Mo is the element which determine the resistance (Tp 317L is ussually used). Is it correct?
Is Duplex acceptable provided that this material has Mo:3% min? Any experience with this material in this service?
Thanks
Peter

 

[0707]

"DSS alloys are used quite frequently in oil refinery heat exchangers. Typical applications are where there is a risk for SCC and localized corrosion as a result of chloride containing process streams, cooling waters or deposits. Additionally DSS offers high resistance to compounds such as hydrogen sulphide, polythionic acid, naphthenic acid, amines and ammonium bisulphate, and has been employed in areas where such species have caused corrosion problems on other materials."

As the (UNS 32205) has 3.2% of Mo against 2.2% of 317L in principle it will resist more to NAC corrosion than the 317L.

luis marques

 

[TomEun]

Please find API TR 938-C, para.5.5. for API discussion and survey

The Mo contents point of view, DSS may be an alternative metal to 317 SS in NAC with ClSCC environment, 600F and below. However the DSS may have to be carefully selected because the industrial data (either problem or no-problem) for NAC of DSS are not enough.