Effluent Cooler Heat Exchanger Material Selection 1

[NARL]

We are in the process of replacing the high temperature effluent coolers in our Hydrogen plant. The exchangers are shell and tube type and we are planning to change the material to address a problem with carbonic acid corrosion. The plan is to install new 321 stainless steel tube bundles in the existing carbon steel (A204 Grade 'A') shells. The tube side environment is boiler feed water with design pressure of 850 psig at 520 deg. F, pH of 7.0, conductivity of 3.0 mmhos/cm, chloride content of 0.52 ppm and sulfate content of 1.0 (there are minor amounts of other impurities generally less than 0.6 ppm). The shell side is 380 psig at 830 deg. F with a product flow of mainly steam (34%), Hydrogen (52%), CO2 (10%) and the balance of CO and C1.

Can anyone give me some advise with respect to the use of the stainless steel material? Can I expect galvanic corrosion due to the different metals, any concerns with respect to SSC or SCC? Any comments would be appreciated.

 

[PAN]

I also worry about galvanic corrosion in your application. Moreover, changing to Type 321 may not solve your corrosion problem. What's the piping material upstream and downsteam of tube side?

 

[NARL]

The piping materials are as follows:

Piping to/from the exchanger tube side (boiler feed water) is carbon steel SA106.

On the Shell side (effluent) the pipe material is SA335 Grade P11.

 

[PAN]

In my opinion, carbon steel tubes should be acceptable.

For shell side, it might be overlaid with 1.25Cr-0.5Mo steel as your piping material.

Could you please describe more about corrosion problem in this application? Does it corrode at tubesheet?

 

[mcguire]

NARL
321 is an unusual choice. It really gets you nothing over 304L in terms of corrosion resistance, but costs more. Consider moving up to 2205 and using a lighter gauge. It has much more corrosion resistance plus it is immune to SCC and has nearly double the strength. You'll improve your heat transfer with it.
I don't know your design enough to comment on the galvanic aspects.

 

Using 321ss sounds like a European solution - it can be cheaper there than in the USA. Suggest that McGuire's answer looks technically the best - but we do not know the economics of your plant.