U-Bundle Heat Exchanger 9

[Inchtain]

Good morning,

We have one U-Tube Heat Exchanger where the tubes made of SS (SA 789) and others like baffles, tie rods shell and caps are made of CS (ASTM 516 Gr. 60).

First, what is the purpose of using the two dissimilar metals for the design?

Secondly, and because of this design the baffles and tie rods were heavily attacked by galvanic corrosion after years of operation, their replacement is deemed necessary now.

Saying that, and in order to insert the new baffles and tie rods to the good condition tubes, I propose to cut the tubes slightly before the tube sheet. So, is that practically acceptable? and what effects on the process and heat transfer efficiency after shortening the tubes by few centimetres?

Cooler details:
Design pressure: Shell 38 bar and Tubes 55.5 bar
Design temperature: Shell 70 degrees Celsius and tubes 170 degrees Celsius
Fluid: Shell Cooling Water and tubes HC+H2O
No. of passes: 1 for the shell and 2 for the tubes.
Capacity: Shell 430 liters and tubes 150 litres
Tubes: Diameter 19.05 X 1.65 - 6096 long.

Best regards,

 

[Christine74]

I don't think that's actually from API 660. My version (9th edition) stops at paragraph 8.1.5. It also doesn't appear anywhere in the 8th edition.

But regardless of where it came from I don't think I agree with it. In most cases the tube metallurgy is set by the tube-side process fluid, not the shell-side fluid (corrosive fluids requiring special metallurgy are typically routed through the tube side). So if you have noncorrosive service on the shell side of the exchanger and a corrosive service on the tube side that requires the use tantalum tubes, does it make any sense to spend big bucks for tantalum baffles?

And as explained above the galvanic corrosion argument is somewhat of a red herring. You don't eliminate galvanic corrosion by making the baffles the same material as the tubes, you just relocate it to the shell. You'd have to make the baffles AND the shell be the same material as the tubes to eliminate galvanic corrosion potential.


-Christine

 

[r6155]

@ Christine74
1) "I don't think that's actually from API 660. My version (9th edition) stops at paragraph 8.1.5”

You think wrong. Check if your version of API 660 is the latest

2) The idea is to protect the most expensive material from corrosion, in this case the SS tubes. CS shell side is cheap and easy to replace.

Regards

 

[Christine74]

R6155,

The "8.1.6" paragraph probably exists somewhere, but it's certainly not in API Standard 660 and as best I can tell it's never even appeared in API 660 (doesn't appear anywhere in the 7th, 8th, or 9th editions). Earlier I referenced the 9th edition, which is in fact the latest version of API 660. Why don't you tell us specifically which version of API 660 you supposedly took that excerpt from?

https://www.api.org/~/media/files/publications/whats new/660_e9 pa.pdf

Also your point #2 doesn't even make sense. If anything, carbon steel baffles would act as an anode further protecting the stainless tubes from corrosion.


-Christine

 

[r6155]

Christine74

Obviously I work with the current edition. You must search well. Try again.

Regards

 

[TGS4]

r6155 - I just looked at my ninth edition, dated March 2015. According to API, that is the current Edition. Section 8.1 ends with paragraph 8.1.5.

You owe Christine74 an apology.

 

[GD2]

Inchtain,

I will try to answer few of your concerns:
1) First, what is the purpose of using the two dissimilar metals for the design?
Ans: cost
2) it is common to always find dissimilar material combinations in a shell and tube HX.
3) SS tubes are for the more aggressive fluid.

Preventing Galvanic corrosion:
When you use new baffles, tie rods etc, use a non-corrosive coating by consulting a coating service company. Tell them about your problem.

For curiosity,
What is the exact process fluid? Is it sweet/sour HC with produced water?
What is your cooling water? Is it surface water or ground water? If surface water, is it sea, lake, river, or pond?

Last but not the least, don’t jump into design error in the very first. It should be the last option after all other options fail.

GDD
Canada

 

[r6155]

API STD 660 MARCH 2015 is superseded by 2020

Best information of dissimilar material in bundle and shell side is in SHELL COMPANY
DEP SPECIFICATION
AMENDEMTS / SUPLEMENTS TO API STD 660
DEP 31.21.01.30-Gen
February 2017

Regards

 

[TGS4]

r6155 - I downloaded the August 2020 Addendum of API 660. Still paragraph 8.1 ends at 8.1.5. There is NO 8.1.6.

This supposed paragraph comes from the IOGP S-614 document you uploaded. It is certainly not an API standard.

 

[Christine74]

r6155,

Another diversion tactic. The Shell DEP specification you referenced doesn't mention anything about baffle materials needing to match the tube material, it only talks about dissimilar welds. And the IOGP standard you linked to earlier obviously is not API 660.

Can't you just admit that you were wrong? Is your ego that fragile?


-Christine

 

[r6155]

@ TGS4
1) You were working with an old standard, did you just notice today?
You should thank me for reporting it to you.

2) What is your help to (OP)?

Regards

 

[r6155]

@ Christine74
1)Please see the Sheel DEP Table 1-1 Materials for use in shell and tube exchangers, page 46 to 50 (total 58 pag in pdf)

2) The IOP and SHELL DEP are better than API 660

Regards

 

[TGS4]

r6155 - I am calling out your incorrect information, as is Christine74. That's extremely helpful to the OP when incorrect information is provided. You have quoted a line in a Standard that doesn't actually exist - which you STILL haven't admitted.

As Christine74 stated, I also believe that your ego is much too fragile to admit that you were wrong.

 

[r6155]

TGS4
You are fired at my company for working to an outdated standard.

Regards

 

[Trestala]

@r6155, I have API 660 9th Ed, March 2015, Addendum 1, Aug 2020 and the Paragraph you're saying doesn't exist.
I even checked my copy of DEP 31.21.01.30-Gen 2013/2014 editions if Shell DEP had added that line in their amendments to API 600 and it doesn't exist either.

Also, why would someone word the requirement as "SHALL be manufactured from material with equivalent chemical composition and corrosion resistance" then add "unless otherwise specified on the datasheets" after.

 

[TGS4]

r6155 - you're working to the current standard, and yet you still managed to invent a paragraph that doesn't exist. That is a fire-able offense in most respectable companies.

Can you please admit that you were wrong so that we can move on?

 

[SnTMan]

Yee-hah

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Caloooomi]

sheesh.

 

Time out

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

 

[Inchtain]

GD2

What is the exact process fluid? Wet Gas
What is your cooling water? Is it surface water or ground water? If surface water, is it sea, lake, river, or pond? The source is a water well (ground).

Additionally, my API 660 copy does not show item 8.1.6

Regards