14 replies to this topic

[s9992029]

Hello, Sirs and madams.

 

I would like to ask about PSV connection having tube rupture case.

Where should I connect PSV if it has tube rupture case?

If the tube is ruptured, the gas will be ingresses into the cooling water and it will be pressurized.

The water and flammable gas are mixed and it should go flare header? or Atmosphere?

 

Let us discuss with this topic.

[breizh]

Hi,

You should have a nozzle available on the shell of your HX to install a PSV!

Breizh 

[s9992029]

Hi,

You should have a nozzle available on the shell of your HX to install a PSV!

Breizh 

you didn't get my point.

Which disposal system is proper for the tube rupture case.? to Flare or Atm?

When it is poping the fluid will be mixture of water and hydrocarbon.

[latexman]

Which disposal system is proper for the tube rupture case.? to Flare or Atm?

 

 

All the standards I've read say to vent to a "safe" location.  What are the risks if the shellside PSV vents to atmosphere?  Is the pressure high or not so high?  Is the flow large or small?  Is it in an area occupied frequently or rarely?  What kind of environmental impact and publicity would a tube failure bring to your company?

 

Tube failures are rare, but they can be quite energetic.  So, is a discharge to atmosphere "safe" in your case?  None of us know the answer.  If not, send to a knock out pot, then the flare.

 

[breizh]

OK , I did not get your point ! What was your proposal ?

 

Is that clear that the pressure on the process side is higher than on the cooling water side ?  

What are the consequences in term of safety if you mix HC and water ?  Still hazardous ? 

What are the consequences if you bring this stream to the existing flare system ? 

How do you intend to separate water from HC before flare , knock out pot ? 

If your PSV is activated and connected to the flare system , how will you know that there is a rupture ?

 

 

It has to be discussed within your organization .In any case should be routed to a safe location .

 

I've attached documents to support your work .

http://www.eptq.com/...de-0ba95c163e75

 

My view .

  

Breizh 

[s9992029]

OK , I did not get your point ! What was your proposal ?

 

Is that clear that the pressure on the process side is higher than on the cooling water side ?  

What are the consequences in term of safety if you mix HC and water ?  Still hazardous ? 

What are the consequences if you bring this stream to the existing flare system ? 

How do you intend to separate water from HC before flare , knock out pot ? 

If your PSV is activated and connected to the flare system , how will you know that there is a rupture ?

 

 

It has to be discussed within your organization .In any case should be routed to a safe location .

 

I've attached documents to support your work .

 

My view .

  

Breizh 

Thank you for your respose.

The process is 300barg ethylene, and utility is cooling water having design pressure 8barg.

If the tube rupture is occurred in the heat exchanger, shell side(water service) is pressurized and then mixed ethylene and water will be carried by PRV.

The question is that there is any Code or Article regarding this issue describing basis of disposal methodology if tube rupture case. Ethylene is not hazadrous but it is possible explosion if concentrated in confined area. Recently, in view of enviormental trend, many goverment and client prefer connect to flare.

 

once again thank you very much.

[Pilesar]

If 300 barg ethylene is relieving through a pressure relief valve because of a heat exchanger tube rupture, then the relief valve discharge should go to a flare. Even if the relief valve is located on the cooling water system, there will be very little water in the discharge because the water will not be able to get to the relief valve against so high ethylene pressure. You may have a little water in the initial discharge, but the water will soon no longer be there and the ethylene will still flow. In such a scenario, you will also have a large temperature drop where the ethylene pressure is reduced and must use suitable materials of construction to handle the temperature. It is likely you will need to route this relief discharge to a wet flare using stainless steel piping. The relief system designer needs to evaluate all credible relief cases.

[s9992029]

 

Which disposal system is proper for the tube rupture case.? to Flare or Atm?

 

 

All the standards I've read say to vent to a "safe" location.  What are the risks if the shellside PSV vents to atmosphere?  Is the pressure high or not so high?  Is the flow large or small?  Is it in an area occupied frequently or rarely?  What kind of environmental impact and publicity would a tube failure bring to your company?

 

Tube failures are rare, but they can be quite energetic.  So, is a discharge to atmosphere "safe" in your case?  None of us know the answer.  If not, send to a knock out pot, then the flare.

 

 

Let me know the standard that you mentioned. I read API521/520, but it doesn't state guidance regarding tube rupture disposal.

If you know, please let me know the standard name.

 

Thanks.

[fallah]

Thank you for your respose.

 

 

The process is 300barg ethylene, and utility is cooling water having design pressure 8barg.

If the tube rupture is occurred in the heat exchanger, shell side(water service) is pressurized and then mixed ethylene and water will be carried by PRV.

The question is that there is any Code or Article regarding this issue describing basis of disposal methodology if tube rupture case. Ethylene is not hazadrous but it is possible explosion if concentrated in confined area. Recently, in view of enviormental trend, many goverment and client prefer connect to flare.

 

once again thank you very much.

 

 

Hi,

 

With such huge pressure difference between low pressure and high pressure sides, you have probably to use rupture disc instead of PSV on the shell side due to a severe pressure spike following to tube rupture.

[breizh]

Hi,

To add to my previous reply , you may consider to take a look @:

Guidelines for pressure relief and effluent handling systems by CCPS  ( Center for chemical prevention safety) , Wiley and Diers.

 

Breizh

[latexman]

Let me know the standard that you mentioned. I read API521/520, but it doesn't state guidance regarding tube rupture disposal.

If you know, please let me know the standard name.

 

That will, or should be, a company standard, or company policy.  And it is not just for the effluent from tube rupture, but the effluent from a relief device for all of it's credible scenarios.

 

Basically, when a relief activtes, no one should be harmed.

[aju_1807]

Wont it be a good idea to design the pipe and weak side of exchanger by 10/13 rule and then water network is open to CW so there is no risk of pressurization. Nonetheless, if we consider routing to ATM it will lead to liquid relief as well which needs to be analysed. This anyway needs to be analysed since routing to flare KO drum will call for further assessment since liquid from flare KO drum will be routed back to process (which means CW will be ended up in process side - presuming flare KO drum liquid is reprocessed).

 

Liquid relief shall be avoided at first place as a good design by rating weak side by 10/13 rule and keeping complete CW network on lower side.

OK , I did not get your point ! What was your proposal ?

 

Is that clear that the pressure on the process side is higher than on the cooling water side ?  

What are the consequences in term of safety if you mix HC and water ?  Still hazardous ? 

What are the consequences if you bring this stream to the existing flare system ? 

How do you intend to separate water from HC before flare , knock out pot ? 

If your PSV is activated and connected to the flare system , how will you know that there is a rupture ?

 

 

It has to be discussed within your organization .In any case should be routed to a safe location .

 

I've attached documents to support your work .

 

My view .

  

Breizh 

Thank you for your respose.

The process is 300barg ethylene, and utility is cooling water having design pressure 8barg.

If the tube rupture is occurred in the heat exchanger, shell side(water service) is pressurized and then mixed ethylene and water will be carried by PRV.

The question is that there is any Code or Article regarding this issue describing basis of disposal methodology if tube rupture case. Ethylene is not hazadrous but it is possible explosion if concentrated in confined area. Recently, in view of enviormental trend, many goverment and client prefer connect to flare.

 

once again thank you very much.

 

[sonu19921103]

As the process side operating pressure (300 barg) is >> than the cooling water side. The tube rupture case can be catastrophic you need to perform a transient analysis to understand the reaction time required to avoid the over pressurization of the shell side (note that the shell will observe a peak transient pressure and if its more than the short term mechanical deign rating of exchanger id may fail even before the PSV/RD acts).

 

Nowdays its a normal practice to design heat exchanges based on the 10/13 rule so as to make tube rupture scenario not applicable. You will realise that designing the heat exchanger is still going to be a cheaper option considering PSV/Disposal system/ Transient analysis and the other costs.

 

Also consider the risk of Ethylene ingress in the cooling water network; ultimately it will end up in the cooling tower where the fire triangle will be complete. Thus a explosion risk.

 

Best Regards

Sonu Singh

[sonu19921103]

Refer the below link for the article addressing the similar issue.

 

A change in heat exchanger is the desired in your case.

 

https://www.thechemi...eat-exchangers/

[fallah]

As the process side operating pressure (300 barg) is >> than the cooling water side. The tube rupture case can be catastrophic you need to perform a transient analysis to understand the reaction time required to avoid the over pressurization of the shell side (note that the shell will observe a peak transient pressure and if its more than the short term mechanical deign rating of exchanger id may fail even before the PSV/RD acts).

 

Nowdays its a normal practice to design heat exchanges based on the 10/13 rule so as to make tube rupture scenario not applicable. You will realise that designing the heat exchanger is still going to be a cheaper option considering PSV/Disposal system/ Transient analysis and the other costs.

 

Also consider the risk of Ethylene ingress in the cooling water network; ultimately it will end up in the cooling tower where the fire triangle will be complete. Thus a explosion risk.

 

 

Hi,

 

Please be informed, 10/13 rule as one of the API 521 rules is no longer applied due to change in new editions of mentioned standard. In seventh edition of API 521 the hydro test pressure of the low pressure side should be equal to or higher than the design pressure of the high pressure side to be able to remove the tube rupture case among the credible scenarios of over pressure in a shell and tube heat exchanger.