sulfuric acid heat exchanger- retubing operation

[mjellali]

hi members,

currently we perform the retubing operation of one of the sulfuric acid coolers (fluid circulation pattern: CO-CURRENT, brend: CHEMETICS, schell side: SULFURIC ACID 107°C/77°C, pressure drop: 1.04 KG/CM3, material grade: 304L, tube side: SEA WATER 31°C/41°C, pressure drop: 0.63 KG/CM3, material grade: 904L)and it's been a period of time we hesitate about wich combination of works for tube to tube sheet joint (welding, expanding, seal or strength types). any help? some photos of the operation's start are given here attached.

Thanks and regards

 

[EdStainless]

Are you changing the materials of construction?
These acid coolers are very specialized. I would never undertake rebuild of one.
Go back and buy a replacement from the original manufacturer.
A very small mistake will result in a life measured in days, if not hours.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[mjellali]

hi Edstainless,

we do not change any construction material, although we only have purchased a new amount of tubes exactly as the old ones wich are of UNS A 249 grade.

 

[metengr]

Use the original code of construction method for joining the tubes to the tubesheet, if this is an in-kind re-tube.

 

[EdStainless]

It just seams odd that you would risk 304 in sea water service.
I am guessing that the original design was NOT intended to be seawater cooled.
These tubes are frequently welded flush with the inside face of the tube sheet so that there are no crevices on either side.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[cmsvessel]

Why do not you buy a new bundle or even a new heat exchanger? From your picture,the parts you can probably re-use might be only the tube sheets. I can provide you a new unit at lower cost than your repair cost.

 

[mjellali]

cmsvessel

some reasons we are proceeding this way are:
-the period of time it tooks to manufacture a new cooler is almost one year
-the new tubes are new provisions of us
-the whole first shell parts are to be reused
-the old tubesheets are not to be reused but other machined new ones are to use
-the cost of this complete operation is about one fourth the cost of a new cooler

so, why not to proceed in this way in your opinion?
what are you suggesting as a low cost to perform this operation with or even to built new other one?

thnxxx

 

[marty007]

Just one quick question, does this exchanger use anodic protection?

 

[EdStainless]

Yes, it uses a lot of CP.
With this material of construction it is the only way that it would survive.
That is usually how these fail, failure of the CP. (or they run the acid too hot, or too dilute, or they pick up some Cl contamination, or about 12 other things)


mjellali,
Are you sure that your replacement materials meet all of the original requirements? (composition, manufacturing methods, NDT methods)
The tube-tubesheet welds are critical, as is the CP system.
I can see you building 4 of these and still not getting it right.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube