<body><script type="text/javascript"> function setAttributeOnload(object, attribute, val) { if(window.addEventListener) { window.addEventListener('load', function(){ object[attribute] = val; }, false); } else { window.attachEvent('onload', function(){ object[attribute] = val; }); } } </script> <div id="navbar-iframe-container"></div> <script type="text/javascript" src="https://apis.google.com/js/plusone.js"></script> <script type="text/javascript"> gapi.load("gapi.iframes:gapi.iframes.style.bubble", function() { if (gapi.iframes && gapi.iframes.getContext) { gapi.iframes.getContext().openChild({ url: 'https://www.blogger.com/navbar.g?targetBlogID\x3d8968604820003269863\x26blogName\x3dChemical+%26+Process+Technology\x26publishMode\x3dPUBLISH_MODE_BLOGSPOT\x26navbarType\x3dBLUE\x26layoutType\x3dCLASSIC\x26searchRoot\x3dhttp://webwormcpt.blogspot.com/search\x26blogLocale\x3den\x26v\x3d2\x26homepageUrl\x3dhttp://webwormcpt.blogspot.com/\x26vt\x3d6402931565399164945', where: document.getElementById("navbar-iframe-container"), id: "navbar-iframe" }); } }); </script>

Chemical Process Technology

Continue to learn tips, knowledge and experience about Chemical Process Technology...

Enter your email address:


CLOSE WINDOW


 

Chemical & Process Technology

A place to share knowledge, lesson learnt...

Sunday, May 23, 2010

Anyone can tell me what will be the set pressure for the spare PSV in the multiple PSV (3 X 50%) arrangement. ? Set pressure for 1st PSV is preset at 100% whilst set pressure for 2nd PSV is 105% of 1st PSV set pressure. Should we set 3rd PSV (spare) at 100% or 105% of 1st PSV set pressure ???


Considering a PSV systems with
  • PSV-1 set at 100% set pressure
  • PSV-2 set at 105% set pressure
  • PSV-3 is spare for PSV-1 or PSV-2.

IF PSV-3 set at 100% set pressure
i) whenever PSV-1 is removed for inspection / maintenance, PSV-3 will be put in service. Then the situation will be
  • PSV-1 out of service
  • PSV-2 set at 105% set pressure
  • PSV-3 set at 100% set pressure
Situation remain same as before. Healthy and proper setting.

ii) whenever PSV-2 is removed for inspection / maintenance, PSV-3 will be put in service. Then the situation will be
  • PSV-1 set at 100% set pressure
  • PSV-2 out of service
  • PSV-3 set at 100% set pressure
Situation slightly different. There is potential of chattering in case relief. However, this situation is intermittent, short period, operator aware and attended and manageable. This is acceptable.





IF PSV-3 set at 105% set pressure
i) whenever PSV-1 is removed for inspection / maintenance, PSV-3 will be put in service. Then the situation will be
  • PSV-1 out of service
  • PSV-2 set at 105% set pressure
  • PSV-3 set at 105% set pressure
PSV-2 or PSV-3 will only start to open at 105% set pressure. This is not acceptable as relieving pressure is exceeded 100% of set pressure..

ii) whenever PSV-2 is removed for inspection / maintenance, PSV-3 will be put in service. Then the situation will be
  • PSV-1 set at 100% set pressure
  • PSV-2 out of service
  • PSV-3 set at 105% set pressure
Situation remain same as before. Healthy and proper setting.

Recommended :
Subscribes to FREE Hydrocarbon Processing
 
RECOMMENDATION
Therefore setting spare PSV other than 100% of set pressure will possibly lead to situation where the initial relieving pressure higher than 100% of set pressure. This is against code requirement and therefore the spare PSV is recommended set at 100% of set pressure.


Related Topics

Labels: ,

posted by Webworm, 9:40 AM

3 Comments:

Anonymous Gary Prager said...

General practice is to have a rupture disc backing up a PSV, particularly when viscious non Newtonian fluids are involved..........gary prager

May 25, 2010 at 5:31 AM  
Anonymous Anonymous said...

Dear Joe Hello/Good Morning,
Although bit delayed (almost a week over) response.
Just a wild thought If PSV#1 is set 100% and PSV#2is 103% and PSV#3 at 105%.
Does that leads to an acceptable scenario;Probably trial worthy.
Regards
SMWA

May 30, 2010 at 9:36 PM  
Anonymous JoeWong said...

@Gary,
Thanks.

@SMWA,
Thanks for your participation...

PSV-1 set at 100% set pressure
PSV-2 set at 103% set pressure
PSV-3 is spare for PSV-1 or PSV-2 set at 105% set pressure.

If PSV-1 out for service, remains
PSV-2 at 103% set pressure
PSV-3 at 105% set pressure

This is not acceptable as relieving pressure is exceeded 100% of set pressure.

May 31, 2010 at 8:21 AM  

Post a Comment

Let us know your opinion !!! You can use some HTML tags, such as  <b>, <i>, <a>

Subscribe to Post Comments [Atom]

Links to this post:

Create a Link

Home:

<< Home