20 replies to this topic

[Ankit_Kumar]

Dear All,

 

Good Day

 

Please find rough sketch of  a vessel being used in one of the plant. I need to evaluate if a PSV is required for vessel for N2-valve fail-open basis. (Split range assembly)

I need the criteria for evaluation. Appreciate if anyone can provide the criteria along with reference. 

 

Regards

Edited by Ankit_Kumar, 13 May 2016 - 06:32 PM.

[Ankit_Kumar]

So many views but no reply         

[fallah]

Ankit_Kumar,

 

Your attached picture couldn't be opened...

[latexman]

What is the pressure of the nitrogen source?

[Sherif Morsi]

What is the design pressure of the vessel?

 

Can you provide more description regarding the process around this vessel?

[latexman]

The sketch says "Design P = 14 kg_f/cm² (g)".

[shan]

The case that PV-A (blocked outlet) and PV-B (losing inlet control) fail simultaneously is considered as double jeopardy case.  You may still need a PSV for the fire case.

[Art Montemayor]

According to the ASME pressure vessel code, ALL pressure vessels (vessels designed to operate above 15 psig) - regardless - require a PSV.  Am I wrong or has this been changed?

[Bobby Strain]

Art,

   I don't think that any overpressure device is necessary if there is no cause for overpressure. In the case of an air receiver, for example, if the air compressor discharge relieving device protects the vessel from that source, and there is nothing flammable to cause a fire, then no device is required. Process engineers have difficulty with this concept, and I have heard much discussion on the subject. I think the outcome of all the discussions would agree with you. And, no, it has not changed. A PSV was never mandatory.

  For the service in question, if none of the input streams can overpressure the vessel, and there is no flammable nearby, then no overprotection device is required. If the nitrogen supply pressure can exceed the vessel design pressure, then protection is required. Likewise, if either of the liquid inlets can overpressure the vessel, this instance requires a PSV. And, of course, any reverse flow from the pump discharge that can overpressure the vessel must be evaluated.

      The query was not well formed. Suggesting that Ankit needs some supervision in his organization to teach him how to conduct an analysis of relief requirements.

 

Bobby

[latexman]

shan,

 

What about a single common cause failure?  The PIT craps out, the sensor gets plugged, the sensor tube develops a leak, whatever, and reads too low and the vent PV closes and N2 PV opens wide open no matter what happens with the real pressure.

 

I think it's credible.  If Ankit_Kumar would answer some questions, we could wrap this one up.

[latexman]

Bobby,

 

The Code may have changed and I missed it, but my recollection is an air receiver is one of the cases where a PSV is mandatory, no matter what.  Pressure vessels in air, water, and steam are specifically required to have a relief device.

 

In other cases, you are right, the pressure vessel can be protected by "system design".  It is called ASME Code Case 2211 which was originally pursued by Dow Chemical.  I attached some information on Code Case 2211, fyi.  To not have a relief device on a pressure vessel and properly comply with Code Case 2211, is quite an onerous task, in my opinion.  I would rather put a small PSV or RD on the vessel and provide the normal relief device documentation and be done with it.

Attached Files

•  ASME Code Case 2211.pdf   79.59KB   80 downloads

[fallah]

According to the ASME pressure vessel code, ALL pressure vessels (vessels designed to operate above 15 psig) - regardless - require a PSV.  Am I wrong or has this been changed?

 

Dear Art,

 

UG-140 in ASME Sec. VIII Div. I allows ommiting PSV for pressure vessels by an appropriate choice of MAWP and/or by safety instrumented system...
 

[shan]

N2 PV should be FC (fail close) and vent PV should be FO (fail open).  Therefore, the PIT malfunction is not a vessel overpressure case. 

[latexman]

shan,

 

In the scenario I described, the PV's did not fail.  They did not lose power or air supply.  The transmitter has failed or encountered a condition to give wrong pressure, and the valves are acting properly.  If the pressure is wrong and low, the vent valve closes and the N2 PV opens.  It is a valid scenario in my little world.

[latexman]

fallah,

 

Is it your understanding that air, water and steam service is exempt from this option, thus requiring a relief device?

Edited by latexman, 02 October 2015 - 07:01 AM.

[fallah]

 

Is it your understanding that air, water and steam service is exempt from this option, thus requiring a relief device?

 

latexman,

 

I think there would be no exemption and if the conditions in this option are met the PSV for over pressure protection can be ommited; regardless of the service in which the vessel has been included...

[latexman]

fallah,

 

Thank you.  The Code has definitely changed from my recollection.

 

As such, I took a little time to review the ASME Code.  UG-140a, where the pressure is self-limiting, allows protection by system design with no relief device.  There is no restrictions on service.  UG-140b, where the pressure is not self-limiting, allows protection by system design, except for air, water, and steam service, unless these services are critical to preventing the release of fluids that may result in safety and environmental concerns.

[Ankit_Kumar]

First of all Thanks to All for ur time & reply

 

I m sorry i forgot to mention N2 value, It is 9 kg/cm2 but i m interested only in the criteria not the actual scenario thats y i didn't provide it earlier. 

 

As per above discussion, following is the criteria (kindly correct me if i m wrong)

 

" PSV/RD is not required on a pressure vessel if any incoming line has max. operating pressure less than the design pressure of the vessel "

 

As i m in interested only on N2 valves fail-open case (not fire case) so in this scenario PSV is not required on the vessel as its design pressure (14 kg/cm2) is above than Nitrogen max inlet pressure (9 kg/cm2). 

 

Appreciate if anyone can share the file of "UG-140 of ASME Code" ???

[shahid780812]

Dear Ankit,
You got it right. By the way what is the basis of 14 kg/cm2 design pressure for the vessel. Is it the design pressure of incoming steam/condensate line to the drum..

[shahid780812]

Further, if it is a water pot,, why is it nitrogen blanketed?
The pot pressure can be floated on the steam header pressure.

[Ankit_Kumar]

Thanks for confirmation.

 

Design Pressure of tank is mentioned in Data Sheet. I don't get what u exactly u r asking regarding ur 1st comment.

 

Nitrogen is provided for sealing purpose to maintain level in the pot.