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ADU overhead Condenser Tubes Failed in Four months of operation 2

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MIANCH

MIANCH

Chemical
Aug 8, 2002
162
Dears
we replaced ADU overhead condenser with new one and tubes failed in four month of operation, shell side is overhead vapors and cooling media is seawater. for detail please see attached pH / Chloride analysis since January 2023. Tube material is SB-111-UNS C70600. There is not only tubes corroded but tube sheet also develop leak. tube sheet material is SB-111-UNS- C46400. Can someone can explain the rapid exchanger failure and its mitigations.
Thanks
 
 https://files.engineering.com/getfile.aspx?folder=0749d2cd-e1cb-4fc6-b587-17fd761b21c2&file=E-103_A_Tube_Failure.pdf
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Screenshot_20230520-092033_dvyb7b.png


I see erosion on your tube inlets. What is your flow velocity in the tubes?

Screenshot_20230520-092130_tlsicg.png
 
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1. What is your tube side velocity?
2. What is wrong with your pH control? (And Cl for that matter)
3. Look at the MTR for you CuNi, I'll wager that it is at the very low end of the strength (and hardness) range.
You need to replace the tubes, perhaps a cold finished version or look for tubes in C70620.
The Iron in the alloy raises the strength. Your 90/10 likely has a yield strength in the range of 14-18ksi.
C70620 will commonly be over 20ksi yield.
You will also need to gently blast the tubesheet and maybe epoxy coat it after retubing depending on the damage.
And slap your installer, the inlet end tubes should be flush or even flared and not protruding.
Some people leave the exit ends with a slight projection, but it does not serve any purpose.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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TugboadEng / Edstailess,
I calculated tube side velocity is very high 2.4 ft/s while in spec sheet mentioned 3.5 ft/sec. more over specified pressure drop is 3 psi while we have 8 psi.
what is further need to be check and how to mitigate erosion / corrosion problem, shall we throttle cooling water inlet valve or outlet valves. our system does has proper water flow control system, we have one main seawater pump and common header for cooling services and outlet going with out back pressure control to sea back.
 
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The pressure drop indicates that your velocity may be higher than what you have calculated. Was this measured before you started plugging tubes?

I feel that throttling the outlet valve would be a preferred option. It creates backpressure on the exchanger which reduces the likelihood of cavitation.
 
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If you throttle is has to be the outlet, you have to keep the exchanger full of water.
But those flows are rather low.
CuNi should tolerate 5-6ft/sec.
Check you math, and check your full flow layout.
You may have other issues here.
Often you see Ti HX running about 8ft/sec, and high alloy SS grades running 10-15ft/sec (when there is enough pressure drop available).


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Naval brass is a fair material for use in sea water, however it is susceptible to dezincification besides, the benefict of tin and some amounts of arsenic aditions. From your foto, I didn´t saw signs of erosion. What was the material of your previous atmospheric destilation unit condenser? Did you colect any leak tube for posterior observation? Did you observed any kind of pitting corrosion?

regards
 
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Tomorrow, I will recalculate tube velocity again and there was operation change during this winter as well, refinery operation team used fired water pump because of seawater maintenance. Fire water pressure was 150 psig. after getting more information from operation team then i will back here.
 
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First things first.

A complete failure investigation is required.

1 Check the MTCs for tubes, tube sheet and shell.

2. Carry out chemical analysis of the above to be certain that they match with specifications..

3 Check whether all QA procedures required for fabrication of above have been complied with.

4. Check the history of the previous condenser. How long was it in service and the frequency/ nature of its failures.

5.Has any change in the feed taken place in the last four months? (like sulphur content or TAN)

6. Were cooling water parameters maintained during the above time period?

7. Process parameters have been amply discussed in the preceding threads.




DHURJATI SEN
Kolkata, India


 
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Dears,
Firstly, i recalculated velocity and result is 3.36 ft/s. this velocity is calculated based on vendor data sheet water flow through the tubes. I agree with EdStainless and Tugboat velocities are much higher because of tube side pressure drop are high that is 14 psi instead of 3 psi.
Water inlet to first pass cracked more tubes (total 80 tubes) as compare to 2nd pass outlet. this indicates, inlet pressure was high enough but Refinery guys told me that they maintained header pressure 25 psig.
Dhurjati sen, I recommended to corrosion engineer shall investigate further as you mentioned because i'm not material specialist.
Hope you guys will recommend more things to check and investigate to find out the material failure.
Regards
 
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Dears,
I'm awaiting more advice for root cause analysis. can someone suggest more items to be checked.
Thanks
 
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I have to rectify the answer of my previous post, with a closer look of course I see erosion on tube inlets and a mixt of corosion erosion on tube outlets. You didn´t tell us yet what was the previous material of your condenser and how long it lasts before. Operation windows and cooling medium were changed (salt water to fire water) tell us which was the operating pressure with salt water and when you started operate with fire water. To Have a good answer on the root cause analysis of your incident you have to tell us all the story and all the variables involved, other wise you are just trowing us fish bait.

regards
 
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Previous material was CuNi 70-30 which is changed to CuNi 60-40. Fire water and salt water both from sea. operating pressure for inlet maintained 25 psig all the time. Previous exchangers were also corroded and leak but not like this.
Hope you have better idea.
 
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C70600 is 90/10.
You need to double check your alloys very carefully.
If someone went from 70/30 to 90/10 to try and save money then this is what I would expect.
There are stronger 70/30 grades such as C71640, C71900, and C71580.
But I suspect that you really need to think about redesigning these HX and look at going to Ti.
But watch out, erosion will still kill Ti tubes.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Mianch

You are in the story, more fish bait is needed, be frank and tell us all the truth, came on!
 
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0707, 1962 this exchanger was designed by Western supply company , Tulsa, Oklahoma, manufactured for chemical construction corporation. Tube material mentioned SB-111. later on this exchanger was manufactured by Thermax and manufacturing date column lift empty in datasheet. I can gauss 30-40 year back. tube material used CuNi 70-30. newest exchanger designed and manufactured by SV-Vila in 2020 and tube material used SB-111-UNS-C70600.
Further sea water analysis checked and we noted pH 8.2, Silica (ppm) 0.6 and Conductivity (uS) 50180.
Now let me know if something is missing to find out the root cause.
 
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Looks like Ed hit the nail on the head. The exchanger was 70/30 and now is 90/10.

That doesn't explain the sheet erosion though.
 
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Erosion can be minimized only with a new design and new operating conditios. About material,try to back to 70/30 grades, for aditional erosion resistance try to use adquated tube ferrules. For aditional analysis to see how erosion/corrosio was developed cut a periferic tube for visual checs.
 
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Where is sea water intake, how far away from sea water outflow exits, and how deep ? Sea water intake also may be contaminated now with bacteria and / or high H2S from short circuiting exit flows ?
 
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Hi George,
which type of bacteria is harmful for CUNI alloy, seawater intake is very near to shore, intake pit (pump suction) pit is enough deep but now days sand reported in pit. we tested silica in lab and found 600 microns g/l.
 
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