Tube side corrosion allowance of heat exchanger 3

[etsen]

In a shell and tube heat exchanger, the thickness of tubes is 2.150mm, but the tube side corrosion allowance is 3.000mm. So I am a little confused now. Could anyone explain it? Thank you very much.

 

[SJones]

Ask a process engineer whether the exchanger will work effectively with 5.1 mm wall thickness tubes. Better still - find out whether the tubes are, in fact, stainless steel and then have very strong words with the person who specified a corrosion allowance. If they are not stainless steel, and 3 mm of corrosion is expected, somebody should have a look at stainless steel.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[gr2vessels]

The corrosion allowance is nominated for all the tubeside components, except the tubes. The tubes corrosion allowance is only specified in special cases and is nominated separate from the general tubeside corrosion allowance. You could run a quick calculation for the minimum tube wall thickness, it would be in the range of 0.xx mm, the rest of, say 2 mm would account for corrosion, erosion and other degrading factors. One solid reason is that the tubes can be replaced in the exchanger with relative ease, should the material loss lead to tubes failure (if that is an acceptable option, obviously).
cheers,
gr2vessels

 

[SnTMan]

Or, at worst, plugged.

 

[etsen]

Because I am not familiar with ASME VIII Div-1 or TEMA or API 660 or GB 151, could anybody tell me something about tube corrosion allowance of heat exchanger and when to replace them by new tube bundles? Thanks a lot.

 

[Christine74]

For shell-and-tube exchangers, a corrosion allowance is typically applied to all wetted surfaces EXCEPT:

1) Tubes
2) Pass partition plates
3) Flange gasket faces
4) Cage (baffles, tie rods & spacers)
5) Floating head cover bolting
6) Split key rings (TEMA "S" type exchangers)

Tundle replacement is generally determined by UT examination of the tubes (IRIS inspection/Ferroscope).

-Christine

 

[gr2vessels]

etsen,
Would you be kind to advise what Code are you using for the design of these heat exchangers (refer to your previous posts regarding the same topic of tubes corrosion).
Cheers,
gr2vessels

 

[etsen]

ASME VIII Div.1 2001ED and TEMA CLASS "C" . Thanks.

 

[etsen]

Thank everybody.
In page 25 of TEMA 1999 Tubular Heat Exchangers, I found these items as follow:

RCB-1.517 TUBES,BOLTING AND FLOATING HEAD BACKING DEVICES
tubes,bolting and floating head backing devices are not required to have corrosion allowance.

RCB-1.518 PASS PARTITION PLATES
Pass partition plates are not required to have corrosion allowance.

RCB-1.52 ALLOY PARTS
Alloy parts are not required to have corrosion allowance.

So I have some questions. 1."Alloy parts" mean they are made of stainless steel? 2. Do tubes have design life? And how can I find the design life in the design document?