Hi there. I hope some one has experience in my problem:

My problem is a failure in the End Fash Gas (EFG) after cooler (38% N2 and the rest is C1). This after cooler cools down EFG from a range of (180- 155 degC) to sea cooling water(SCW) temperature (SCW temp varies from 23 to 33 deg C). The EFG is cooled to around 40 degC.

EFG is in the shell side, whereas the scw in the tube side. It is a counter-current heat exchanger, with two tube passes and one shell pass. Tube material is 70/30 Cu-Ni alloy and the shell material is Carbon steel.

This after cooler suffers from pitting corrosion in the top row of tubes, underneath the shell inlet nozzle.

The EFG flow varies from 850 T/D to 1,400T/d at an inlet pressure of 24.5 barg while the SCW flow is always kept constant at 84 kg/s with an inlet pressure of 3.5 barg.

My question is: we have 3 trains of LNG and the faliure of this exchanger take different years to fail from 1.3 year to about 3.5years.

Can somebody share information with me on the same problem? Any root cause, or a solution to avoid it in the future? Anything would be of help.

Pitting corrosion getting severe at elevated temperature. The top row meeting high temperature gas may result localised high skin temperature if the design is not correct...

Thanx,
This is exactly what happened bu I could not understand why the heat exchanger in one train fail after 1.5 years and in the other train fail after around 3 years.

They are many factors affecting it :

- Quality of tube
- how the gas impinging tube
- Is there any liquid droplet impinging directly on the tube
- stress level for each tube may different from tube to tube and heat exchanger to heat exchanger
- the condition of tube before it is fabricated
- how often is temperature cyclic
.
.
.

So it is very difficult to judge...

Dear, May I just suggest to check the trajectory of gas flow in case of the two equipments in question that might actually be varying greatly showing this vast difference of residual corrosive impact descibed.
Best regards
Qalander

Gents,
For the design of the three exchangers are exacatly copy & paste.
the only thing which I can agree with you is the temperature & the frequency of that temperature becuse I could found an extra 10 degC for the 1.5 yrs Heat Exchanger compering to the the 3yrs HE.
In addition, the 3 yrs HE conditions are almost close to tube film temperature of 52degC and @this temperature the fouling tendecy of scw water increase and this fouling my work as an insulator to the heat transfer and reach the meatel tmperature of 90degC at which the phenomenia of hot spot corrosion occured.
For the 1.5 yrs HE the condition of the 3 yrs HE are aleardy exceeded by 10 degC which may will increase the film temperature more than 52degC and higher fouling tendency may occure and lees life time.
This is my imperession about this problem but I need more ideas to look at the problem from different ahgles.

Any helps is realy appreciated.

Thanks againn for everybody supporting me.

hi there you can contact nalco whitch can provide for you a corrosion inhibitor .i don't know if they have a product compatible with your proces but i think you must give it a shot