Seal Cooler

[seungwon2]

There are some troubles in seal oil cooler with cracks.

It would be appreciated if you kindly let me know of the following;

1)During the tube bending process, what kind of method is used?

- hand bending or CNC bending machine or others

- any heat is applied or cold work is done

2)About design

- Is there any gap between tube outer diameter and shell inner diameter

(I think the clearance of it should be minimized for better fluid velocity)

3)After forming tube, stress relieving or other heat treatment is needed related SCC (Stress Corrosion Crack)

Tube Material is S.S 316L.


Cracks of the coolers has founded top of the tube and the service temperature is above 150’C.

Cooling water condition: Chloride contents average 100ppm



Thanks in advance

 

[checman]

seungwon2 At that temperature your seal cooler is a boiler. It may be possible that you are at times flashing off or degassing and creating vapor pocket in your seal pot and possibly forming chloride salts on your tube, especially if you are using softened water. In any case with chlorides, chloride stress corrosion is possible and very destructive. I have always stayed away from water as a coolant for my seal pot on applications over 250 deg. F. as a general rule of thumb. There are many possible problems with expansion, degassing, flashing, the minerals left behind and more stuff than I have time to get into . A large delta T whether it is in your product being sealed or your seal pot cooling water generally does not give you the result you were looking for. Stuff precipitates out volumes change and a stable environment for your seal is not achieved. I would look into air coolers and get a seal that is made for the temperature you may see. Mechanical seals can be specified to easily handle temperatures of 150 deg C. You can generally remove enough heat with an air cooler to keep the temperature in stuffing box or seal chamber within reason.

Regards checman

 

[Scipio]

My first suspicion is checman is correct. At 100 ppm, the chlorides are probably low enough not to induce SCC, however at those temperatures there's a good chance vapour pockets are forming in the coils, dramatically increasing localized concentrations. Do you monitor the temperature of the return water to see how close it is to it's flash point? Air coolers would be a good way to avoid using the cooling water, another option is to get a seal cooler with duplex or super austenitic (AL6XN) coils. If nothing else, it would eliminate the potential for SCC due to chlorides.