Materials selection for a heat exchagner.

[kissjxp]

Heat exchanger shell side: cooling water (Maximum Operating Temp. 40C). The cooling water has 1500ppm maximum Chloride and 60 wppm Oxygen.

Heat exchanger tube side: caustic (Maximum Tperating Temp. 146C).

We selected carbon steel for the shell and alloy 600 for the tubes.

In order to avoid the galvanic corrosion, we can not use carbon steel for the baffle (Cross).

My question is if we can use 304 or 316 stainless steel for the baffle. Considering the temperature (40C) and non pressure bearing, we do not need to worry about the stress corrosion cracking induced by chloride.

 

[EdStainless]

Do you really want to use 600? Hou strong is the caustic?
That part aside, why don't you look at 2205 for the internals. It won't cost much more and it will actually hold up.

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Plymouth Tube

 

[TomEun]

- Tubes ; Alloy 200, 201, 400 and 600 may be considerable per the concentration in this service. 2205 DSS may be considerable in diluted NaOH.

- Baffles : The severe crevice and pitting corrosion at the gap between tube outsides and baffle holes in 304/316 SS baffles expected. It may create a vibration issue. 2205DSS (or same as tubes’) is recommended.

 

[EdStainless]

The absolute best tubing for severe caustic service is E-Brite (26-1). But if you don't need that level of performance then you don't need to spend that much.

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Plymouth Tube

 

[itdepends]

How strong is the caustic and is there a reason your cooling 146degC caustic with cooling water at 40degC? (Rather than running the caustic against something else to bring the temperature down to a reasonable level first before using cooling water- that's one heck of a temperature difference).

Depending on the caustic concentration- it is common to use carbon steel (to ASTM A179) in heat exchangers operating up to 145degC in alumina refineries and up to 175degC over long periods (plants in service >20yrs). It does depend however on the free caustic concentration.

Cheers

 

[0707]

Before going to the alloys already posted by other, why don´t you try ASTM A179? I agree with itdepends-


regards

Luis Marques

 

[kissjxp]

The caustic is 10%. It also has ~10% sodium salts.

 

[itdepends]

10% caustic is higher than I have commonly seen operated at elevated temperatures. The plant I have experience with generally tops out at 8% at those temps. There is some new equipment that operates at >10% at those temps- but I'm not aware of the materials of construction and it hasn't been operating long enough for me to be comfortable giving an opinion.

That's not to say it isn't done elsewhere (146degC and 10% caustic).

Cheers.