Hot Oil Cooler -Tube Rupture Case.

[gleng]

Does anyone out there use water for hot oil cooling? If so, how do you reconcile tube rupture relief case? (Note: client intends to used double tubesheet to prevent issue at tube-tubesheet joint, but this doesn't address a tube failure).

 

[nickelkid]

A shell side rupture disk is common, I believe Fike is leader (at least that is who I am familiar with)

http://www.fike.com/pressurerelief.html

 

[tkdhwjd]

Make sure that the low pressure side (I will assume that LP side is shell side) is protected against the potential overpressure by tube rupture. Pressure relief devices (rupture disc or relief valve) can be considered unless you can prove that relief path to other system is provided at all times (including start up, shutdown, and normal operations.

 

[gleng]

I understand the need for relief, I'm just concerned about the reaction time of the relief device when water is mixed directly with the hot oil? Is a rupture disk better for this application?

 

[JoeWong88]

gleng,
Finally you speak out what you really concern about...

Liquid is incompressible located at shell side (assumed low pressure side - LPS), severe surge would occur in the event of sudden tube rupture. Surge pressure would exceed the MAWP of the HX. However, there are some allowance in short term pressure excursion (if your HX designed to ASME). If the surge pressure is not very high and surging time is short enough, then your HX is still have no issue with PSV.

PSV is known as "slow" acting device. Rupture disc is far better. However, there still some report indicating that there are some condition where RD still can not works as it wish... Anyway it is still the best device we have now...

Read more in "Tube Rupture : Pressure Relief Valve (PSV) or Rupture Disk (RD) ?"


JoeWong
Chemical & Process Technology

 

[gleng]

The more I think about this issue, the more questions I generate. The way I see it, there's no possible way to prevent a pressure surge caused by the direct contact of hot oil (650F+) with the water. If you put a rupture disk on the low pressure side (in this case the water side) once it releases- it leads to substantially more mixing of the oil and water - more problems, including emptying oil and water systems out the disk discharge line, as it cannot reclose - not a good result. No matter what size valve you put on this equipment, you can't stop the repeated surging that will occur at potentially very high pressures during a tube rupture- therefore, I don't see any practical way to protect the equipment for this case- I hope someone can change my thinking on this.

 

[JoeWong88]

gleng,

Looks at Chernobyl nuclear power plant explosion, is this incident catastrophe ? Looks at Piper Alpha platform fire, is this incident catastrophe ?...and many others. Are these incidents stopping human being to built nuclear power plant and oil & gas platform. NO. Why ? Human being enjoy the beauty of these development while exposing themselves to RISK. On the other hand, human being manage and reduce the RISK and associate CONSEQUENCES.

Similar you have a surge during tube rupture. You are aware of it will create catastrophe to you. Then you have to provide necessary measures to manage and reduce RISK and CONSEQUENCES with best available, reasonable, practical and achievable measures. You do not leave it there without doing anything. For example, you have a kid. He has some friend who always take opium. What will you do ? To me, i will start to discuss and understand him, educate him about opium, monitor his daily activity, etc. Why i do all these, because i knew it possibly cause catastrophe to my kid. I try to manage and reduce the RISK and CONSEQUENCES.

Another thing, let say you are the operator who is going to take care this heat exchanger. Everyday, you stand beside this HX. Now you know there is tube rupture and surge can bring catastrophe... can you imagine you are just beside the HX when tube rupture occur ? Chinese people said "You don't feel the pain if you never touch any hot plate". I am sure there are some in your own language. Come on let think about it.

Tube rupture risk and consequences can be managed and reduced. You put RD to reduce the surging risk. But this bring disposal problem. You may consider to install a surge drum at the outlet of the RD and shutdown all pressure sources in the event of relief. Read more in "Another Way to Manage Liquid Disposal Cause by Tube Rupture"..

I hope above is not too heavy to you and other reader. If yes, please ignore what i have written.

God bless & good luck.





JoeWong
Chemical & Process Technology

 

[gleng]

JoeWong88,
I think you are missing the intent of my posts. I'm basically coming to the resolution that:
1. Firstly, hot oil coolers should not use water if the tube rupture relief scenario cannot be adequately handled.
2. A rupture disc makes a worse condition (less safe) for this particular scenario
3. There's no point in providing a large valve for this tube rupture case if it will not protect the equipment any better- size valve for next largest relief scenario.

 

[chief]

Hot oil coolers are common attachments in diesel engines, turbines, HPU'S etc. They are cooled, usually on the tube side by either fresh water or sea water. The water flow is usually regulated to 10ft/sec, max. to reduce erosion and turbulent aerated flow. Preferred control is by the outlet valve to facilitate this..
To prevent x-contamination of the oil, the design practice is to ensure that the oil pressure exceeds the water pressure.
A tube leak is detected by a gradual drop in the oil reservoir level. Catastrophic tube failures are very rare,but a burst disc on the water side is sufficient protection, with the drain to a safe area.

Offshore Engineering&Design

 

[ggordil]

gleng

I think one point that has yet to be mentioned is that, relief valves and rupture disks are installed to "buy time" before a catastrophic failure. If you install a relief valve for fire, it will not put the fire out, it will buy you some time before the vessel fails (at least in theory). The same for many other scenarios, blocked outlet, tube rupture, control valve failure.

When you design overpressure protection, you are looking to give operators time to intervene to fix the problem. In your case, time for the exchanger to be bypassed or for the hot oil circulation to stop or maybe something else.