Corrosion erosion 5

[MIANCH]

Hi alls
in my refinery we have naphtha cooler and facing problem for rapid corrosion and erosion and tubes leak. shell side is naphtha and tube side is seawater. tube side material is copper nickle alloy.
Naphtha inlet temperature is 320 F and out let is 100 F while seawater in let is 70-80 F and outlet is 130 F.
can any one explain main reason of high rate of corrosion and tube leak.
Best Regards

 

[MJCronin]

Some questions:

1) Was this HX designed for this specific service or has it been bouncing around the plant for a long time with periods in the bone yard ?

2) Can you share with us the drawing ? Is it a TEMA standard design ? If so which one ? Is it a TEMA BEM ?

3) What are the design and operating pressures on both sides of the HX ?

4) What specifically are the materials ? "copper nickle alloy" is not good enough.

5) Because of accelerated corrosion, there are maximum recommended velocities of liquids for various materials contained in design guidelines. Has anyone calculated your actual liquid velocities and compared them to the maximums recommended for your "copper nickel" ?

6) Are there many plugged tubes ? Plugging tubes increases the liquid velocity on the remaining tubes and shortens their life.

7) Where, specifically is your corrosion ? Tube entrances ? shell nozzles ? where ?

Not enough information ......

When you have trouble with your truck, do you tell your Mechanic "Truck broke ... not move"

MJCronin
Sr. Process Engineer

 

[mk3223]

Strongly suggest to have an expert to collect all process and operation info related to the damaged tubes, perform a failure analysis for the root cause of the failure, and provide an engineering solution.

 

[MIANCH]

Hi,
MJcronin,
This HX is very old (you can't image it, because this refinery is in operation since 1960, very little details are available from old guys, I checked personally no detail was printed on name plate but i will ask and share here if got some information.
Operating pressure: 75 psig
Operating temperature: 260 F but now they are operating at 320 F. cooling water is coming from seawater pump discharge and there is no particulate filter.
I asked to one senior guy here in refinery he told me that tube material is copper nickle alloy. I went in workshop and found the same material as said by senior guy.
This refinery is very old fashion refinery designed by EXXON and initially operated by ESSO but now days being operated by Libyans.
MK3223,
Can you please share your past experience for root cause analysis what are the main points of tube failures of this type of HX.
Regards

 

[EdStainless]

Copper Nickle either 70/30 or 90/10 is velocity sensitive. These are not very hard alloys.
There are published velocity limits, but be aware that even at the published limits the tubes are expected to erode.
Typically if they can keep the general wall loss down to 0.0005"/yr they consider it useful.
320F is getting rather hot for CuNi, and very hot for seawater cooling.
This will scale like crazy at 130F.
There are alloys that are much more erosion resistant, but you still need to address the scaling.

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P.E. Metallurgy, Plymouth Tube

 

[Dhurjati Sen]

Dear MIANCH,

Find out and go through the data card and history card for this exchanger.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[MIANCH]

Tube material is admiralty SB-111-C70600 (90/10 copper nickle alloy). And HX type is TEMA AEP.
these photos are visual observation, today i will try to get more information then share with you guys for more discussions.
Regards

 

[Metalero]

it seems like localized corrosion due to condensation. You must identify why in that specific places.

Collect deposits, corrosion products, clean damaged metallic surfaces to confirm/discard flow assisted corrosión or erosion.

Take a look inside the exchanger or in the surroundings for leaks or other sources of fluid taht could be the origin of the mechanism.

 

[MIANCH]

Marriolav
for your information this exchanger is condenser, Naphtha vapors are being cooled down in this exchanger, yes condensation is there as you said.
May be naphtha contain H2S and water vapor and while condensing this create localized corrosion.
I would like to listen from you guys how to avoid this problem and what actions need to be taken for trouble shooting.
Regards

 

[MJCronin]

This 60 year old heat exchanger is at the end of it's design life .... It must be replaced ... nothing lasts forever.

You seem have what is typical of most process plants .... all of the drawings are gone, no maintenance records exist and all of the nameplates/dataplates have been ripped off. Maintenance departments all over the world do this because it ensures that they will never have to work on the equipment (no information) and the problem then can be kicked downfield to the engineering consultant

I suggest that you hire a HX consultant and at least get the cost for a new TEMA AEP Seawater duty unit with an upgraded tube material. You will have to establish the necessary HX duty

I believe that you consider a slightly larger diameter replacement HX made from a superaustenitic SS, or perhaps titanium, or perhaps C276. A larger diameter/number of tubes will mitigate the erosion problem. A material upgrade will ensure corrosion.

Now, your MBA boss will tell you that he doesn't have enough money and scream at you that you "must come up with another plan !!!! "

His extensive background in taxes and accounting are no help to him here ...

Explain to him that the only alternative plan is to rebuild the bundle an be prepared to replace it every 3 years ...

MJCronin
Sr. Process Engineer

 

[MIANCH]

MJCronin,
The last sentence sounds appropriate solution.
Best regards

 

[MJCronin]

MIANCH ..... Buy this superb book and read it:

https://www.amazon.com/Tubular-Heat-Exchanger-Inspection-Maintenance/dp/0070017786

MJCronin
Sr. Process Engineer

 

[EdStainless]

MJC is on the money, except that the rebuilt units won't last any 3 years at the new operating conditions.
They changed the process, now change the equipment. period.

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P.E. Metallurgy, Plymouth Tube

 

[mk3223]

IMO, the best practice of the risk based inspection (API-580) may be implemented to the heat exchangers service in your plant, and to improve the operation efficient and safety.

 

[MIANCH]

Hi All,
Thank you for your valuable comments.
Best Regards

 

[Chumpes]

Hello
Can Cu-Ni 70-30 and 90-10 alloys suffer severe corrosion by water containing H2S ? I heard that sulfur species may corrode copper alloys quite fast, do you have good experience with copper alloys seawater coolers condensing sour water, for example in hydrotreating units ?
Same question for Monel, Alloy 400, Ni-Cu 70-30...
Thanks
Regards

 

[EdStainless]

Yes, H2S will cause the passive film on Cu alloys to become very soluble leading to very rapid metal loss.
Read the Special Metals Monel handbook, the information is there.

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P.E. Metallurgy, Plymouth Tube

 

[Chumpes]

thanks Ed
I cannot find Special metal Monel Handbook after seeking on their website...

http://www.specialmetals.com/assets/smc/documents/PCC-8064 SM AlloyHandbook_v07.pdf

does not give information.
regards

 

[EdStainless]

Chumpes
Try this one

http://www.specialmetals.com/assets/smc/documents/sm-aqueous-corrosion-book.pdf

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P.E. Metallurgy, Plymouth Tube

 

[MIANCH]

Dears,
Here is two more picture for another exchanger for same service, E-103A, its type is TEMA R.
Hot inlet side have copper salt but outlet side no salts deposited.

Regards