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

 

[EdStainless]

Simply looks like they have gone beyond the max service temp for CuNi in this application.

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P.E. Metallurgy, Plymouth Tube

 

[MIANCH]

Edstainless,
Operating temperature is 250F , and water inlet temperature is 75F, H2S is 190 ppm, can this temperature (250F) and H2S destroy like this and rapidly, please elaborate the phenomena bit.
Thanks

 

[TugboatEng]

It only takes a few PPM (0.5 ppm or greater) sulfide to start corroding CuNi at any temperature.

https://pdfs.semanticscholar.org/a0ea/2e5be6d786afb3c4674ff3bd20ddccd26af9.pdf

 

[EdStainless]

H2S is extremely reducing, when some of the oxygen is removed from the oxides and hydroxides that protect the surface the film them becomes soluble and metal dissolves rapidly.

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P.E. Metallurgy, Plymouth Tube

 

[MIANCH]

Additional information today I received,
Cl-:6-18
Ph:4.5-8
I requested to check more samples also for water side and process side as well. Low Ph is not always but some days go down.
Regards

 

[EdStainless]

Low pH is murder on CuNi.
What also happens is that one film will form, but when the pH shifts most of the original film will slough off and be replaced by one with a new composition. Each of these cycles removes more metal also.

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P.E. Metallurgy, Plymouth Tube

 

[MIANCH]

Naphtha Drum boot water analysis has been carried out as per below and I'm very new bundle of tubes will also soon start leaking.
Water Ph: 4.6
Iron content (ppm):4.8
SO-2ppm):----
H2S (ppm):0.42

Seawater
Ph:8.0
Iron (ppm):1.1
SO4-2 (ppm): 3205.5
H2S:0
Please comment on this issue.
Regards

 

[EdStainless]

Why is the pH so low?
You need to start looking at other alloys.

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P.E. Metallurgy, Plymouth Tube

 

[MJCronin]

Explore the replacement of the shell-and-tube design with single or multiple plate frame HXs..... the design pressures and temperatures seem to be within the plate frame maxima.

Make sure that the plate frame unit has additional "rack space" available for future HX expansion...... should your process condition change yet again

You will free up additional floor space in the plant...

Use C276 for the plate material and PTFE for the gaskets ..... keep spare plates and gaskets and instruct plant personnel on how to repair the unit.

Do the job right .... install a new functioning duplex SS strainer on the seawater side and clean it frequently evaluate the new pump operating points on both sides of the HX and adjust existing pumps accordingly....

Or .... like EdStainless says, be prepared to replace thetube bundle frequently if you want to stay with your exsiting MOC

https://www.platetypeheatexchanger.com/plate-type-heat-exchanger-advantages-and-disadvantages.htm

MJCronin
Sr. Process Engineer

 

[TugboatEng]

Titanium has always been the go to to plate material for sea water applications. C276 seems expensive for this application.

 

[MJCronin]

Tug .....

C276 has come down in price, but TI may be a better choice .... you have to get prices of material alternatives and compare

My point, of course, is to do some REAL ENGINEERING, develop and price different alternate designs and come up with a plan.

Yes, this will cost money .... compare the plate frame prices with a tube bundle made of the correct material.

Sixty years ago plate frame HXs did not even exist and may be a good alternative for this ever-changing corrosive application.

It will easy, cheap and simple to do this HX evaluation ..... My question is, why hasn't it already been done ?

MJCronin
Sr. Process Engineer

 

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.

I emphatically concur.
Failure analysis is not done by committees or by crowdsourcing.

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

Absolutely; 60 years is far beyond what can reasonably be expected from chemical process equipment. Bite the bullet and replace the entire HX. The best guide to alloy selection will come from petroleum corrosion engineers; the best industry source for this information is NACE (or else Steve Jones on Eng-Tips).

Bear in mind that the quality of crude oil has degraded massively in 60 years, and many equipments have been forced to climb what I call the 'alloy ladder' to keep up with ever more aggressive raw materials.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[MIANCH]

Ironic,
Look 60 year mean dose not this exchanger is 60 year old, i collected information for this exchanger more in detail and found that there is three exchanger for same service and frequency of tube leak is very high (say every six month or year refinery guys repair or plug tubes and replace the tube bundle with refurbished tube bundle)
Corrosion department in refinery is failed to establish the root cause of failure, last month they requested to process engineering department to investigate the root cause.
I receive very good recommendation and found that localized corrosion is the main cause of failure of this corrosion, old system is existing for crude oil distillation column overhead corrosion control that is ammonia injection. Ammonia is not very effective for overhead ph control while H2S condensing in the presence of water reducing the ph to below 4.5.
tube side is seawater and shell side column overhead vapor containing 190 ppm H2S and water,I think you have better history of this exchanger to understand failure causes.
Regards

 

[TugboatEng]

Here is a study that is very closely related to your situation, low pH high H2S.

https://www.google.com/url?sa=t&sou...Vaw3OM_w7FRfhkPVu5ICGAWRQ&cshid=1563924865867

 

[MJCronin]

Tugboat ....

Based on your fine paper, I stand corrected .... C276 does not seem to be a good choice for this extremely corrosive service. Because of corrosive conditions ON BOTH the tubeside and shellside, the titanium option seems best

Please note that I still recommend paid engagement of an experienced corrosion specialist, developing a report and following those recommendations.

On a parallel path, I suggest getting a budgetary quote on a replacement HX with Grade 2 titanium tubes, titanium clad tubesheet and having a surface area about 10-15% greater than the existing units.

Find the number of weeks necessary to get delivery of a replacement unit

MIANCH

Again, I suggest that you perform an economic evaluation of all of your current replacement and repair costs for replacement tube bundles.

We now understand that there was tube plugging as the bundles degraded, thereby increasing the fluid velocity on the remaining tubes and accelerating corrosion.

Please respect us ... Do not simply drop this thread

Tell us of your final solution and your reasons for selecting it ....



MJCronin
Sr. Process Engineer

 

[EdStainless]

I doubt that you will need more surface area with Ti.
Ti does have very poor fatigue resistance. Ask to see vibration analysis on the new HS+X, especially if they suggest thinner walled tubes in Ti.
With this small of unit they may use a solid Ti tubesheet.

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P.E. Metallurgy, Plymouth Tube

 

[MIANCH]

EdStainless
MOC change already suggested by corrosion department but it was rejected because of costly. I suggested to install micro filter but operation is reluctant to install due to frequency of plugging & cleaning. Ammonia carbonate is being injected to control pH but looks not working very well.
Regards

 

[EdStainless]

If I had a list of everyone that I have seen that is willing to spend millions of dollars on repairs and downtime rather than spend thousands on the correct equipment it would make your head spin.
Often the issue is that people do not report information accurately up the chain of command.

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P.E. Metallurgy, Plymouth Tube

 

[MJCronin]

EdStainless ...

This thread is a waste of time. We ask for informaton ... and we are ignored ! ... We make suggestions and get "Oh, management doesn't want to do that" .... "management says this will be too costly."

This is yet another third-world game ....


MJCronin
Sr. Process Engineer

 

[MIANCH]

MJCronin
I posted all information which I have it, even though I posted photos of exchanger. My area of responsibility is limited. working in MENA is not easy.
MOC change should be accepted by operation not by process engineering or corrosion department.
What you say about, if refinery a is being operated without flare system since commissioning 1960.
Best Regards