Usage of SS304 tubes ot SS316L tubes in cooling water exchangers

[Praveen, Integrity engineer , Refinery]

Recently I observed that in one of the cooling water exchanger (tube in tube) which has Hydrogen at 230DegC on the outer tube and cooling water on the inner tube. The tube metallurgy was SS304. 

Where as in another unit, a cooling water exchanger with SS 316L tubes had lean amine on shell side. 

On what basis is 316L tubes chosen over 304  tubes when a cooling water exchanger is designed?

 - I have two things in mind as far as corrosion is concerned, one being ClSCC and another being PTASCC. 

[Ramin Kondori]

Hello,

I am not familiar with this particular design and Hydrogen process piping is not this simple but as a general role, 304 has less ferrite in its microstructure (comparing to 316 which has 5-10% ferrite). This might have been the criteria to choose 304 over 316. Hydrogen embrittlement affects ferritic microstructures while austenite is immune to this failure mechanism. 

Regards

Ramin  Kondori

Sr. QA/QC & Welding Engineer

-----------------------------------------------------------

PG-Dip. in Welding Engineering (IWE  AT  0070)

BSc. in Civil Engineering (IUT)

BGAS Painting Inspector

ASNT Level I&II

                        

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[Praveen M.N.]

Thank you Raman for your insights. 

I am further looking into use of stainless steel tubes in cooling water service. I was also asked a crude question on these lines without enough data to be honest. They want to use SS tubes in an Ethanol plant and I don't know whats on the shell side but the doubt is for the tubes to be used and the choices are between SS304 and SS316 for a shell inlet temperature of about 120 deg C. Hence the question.

Thanks again 

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- Praveen .M.N

[Kannayeram Gnanapandithan]

in 304 only Cr is ferrite former whereas in 316, both Cr+ Mo are ferrite formers.

THANKS & BEST REGARDS,

KG.PANDITHAN, BE, IWE,  CSWIP 3.1,

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