Titanium compabloc plate exchanger in FCCU main column head service

[aldocigna]

These exchangers cool the main column head gas by water sea
Alfa Laval proposed 3 Titanium welded plate exchangers for this service (Compablock Titanium grade 1 plates , T=80-100 °C, 3000 ppm h2s, 1500 ppm Nh3, <10 ppm CN, 0 ppm Cl).
API 571 par 5.1.3.2 advise for hydriding risk (NACE MR175 par. 4.2.1.4 too) in hydrocarbons side.
What's your experiences about it? Is the grade 1 the best grade for this service?
We actualy use Saf 2507 tube exchanger but we have seen crevice corrosion under gasket in floating head area in sea water side.
What material do you think better?

tx Aldo Cigna

 

[EdStainless]

Not an answer to your question, but what material is corroding under the gasket? Isn't this area overlayed with a Ni-Cr-Mo alloy to prevent this? For that matter why not use a different style of exchanger and eliminate the floating head.

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Rust never sleeps
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[aldocigna]

The corrosion under gasket is a typical corrosion form named Crevice. It's the main problem for this type of austenitic or duplex steel in sea water enviroment (Cl- presence) with high operative temperature (>70°C reached in this case limited no-flow zone of floating camera under gasket). The actual material of tube sheet and floating head is SAF2507 (Super duplex steel) that is better than AISI 316L but not sufficent. Many refinery equipment use this steel in exchanger between sea-water and hydrocarbons with H2S or NH3 presence. In fact the copper alloy is a bad choice with H2s or NH3 and carbon steel with resin internal lining (Saekaphen type) give many other problems.
Often there is now a very good solution. I believe in the Titanium welded plate exchanger propose but in this case there is the hydrading risk, if > 80°C

 

[EdStainless]

I have seen superduplex, superaustenitic, and superferritic tube bundles in seawater heat exchangers. If they were floating head the area of shell under the seal was machined and then overlayed with a "C" type Ni-Cr-Mo alloy to prevent crevice corrosion.
today there is no doubt that at this level of corrosion resistance the superferritic alloys are the most economical.

My only thought about your use of plate exchangers concerns your cooling water, is it clean enough? You will have very small passages and no way to clean these out.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[aldocigna]

We used many hastelloy C276 gasketting plate exchangers in other service (H2SO4/sea water). We had many problems for crevice.
Now we are evaluating the propose to use a new titanium welded plate exchanger (compabloc) in FCCU Head main column service.
I haven't any experiences about this new type. Alfa laval tell easy cleaning operation.
After unbolting the four heavy closure steel plates, it is possible clean all flow channels by high pressure water.
The flow area is bigger than in traditional exchangers (ND max 3/4")
In any case, I think that, in our case, the cleanig is no a true problem because we have three different exchangers lines but only two are sufficient.
I believe that the most important problem is the corrosion problem because the plate thickness is lower than in the tube case and is no easy to blind it
The titanium plate choise is a very expansive one. I would be sure.