Identification of PSV sizing case 1

[e43u8]

I currently have a challenge with our Process department in the company i am working on about the responsibility for identification of PSV sizing (or controlling) case. I strongly claim that action is absolutely the duty and responsibility of process engineer but they believe the action is the responsibility of Instrument engineer. You are kindly requested to 1)submit your opinion about this matter and 2) introduce valid reference(s)to clarify that action is responsibility of which departmet: Instrument or Process?

 

[don1980]

I've seen that it's common for engineering companies to assign safety valves to the instrument group for purchasing (and sometimes sizing based on data provided by process), but I've never seen a case in which the instrument department did the scenario evaluation. Of course, scenarios need to be identified and evaluated by engineers who have good process design knowledge and skills. I've never encountered an instrument engineer who had such knowledge and skills, or a case in which that was an expectation.

Where I work,instrument engineers have no involvement with PSVs. When I've worked with engineering companies that aligned PSVs with the instrument dept, the instrument engineer was never involved in the risk assessment or scenario evaluation - that was always done by process engineers, so I didn't have any concerns.

 

[e43u8]

Thanks a lot don; i am thinking like you as i mentioned. Actually i think identification of PSV sizing case and relevant preliminary sizing for identified case using API 520 equations should be done by process group and PSV purchasing included verification of process sizing based on data provided by process, should be done by instrument group using PSV sizing softwares.

 

[Latexman]

e43u8,

Your first post at ET. Welcome aboard!

If you were to list EVERY duty or work process step needed in the identification of PSV sizing (or controlling) case, and then for each step indicate which Engineer, Process or Instrument, is likely to possess that skill as a natural function, experience, education, or training of their job; I believe the Process Engineer would come out on top. For a start:

Work Process..........Process..........Instrument
M&EB........................Y
P&ID mark-ups...........Y.................Y
Reactivity...................Y
Chemical Propeties.....Y
Simulation Software....Y
Fluid Flow..................Y
Electrical......................................Y

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[Latexman]

If you want the above analysis to carry more weight and be less biased, ask an Instrument Engineer to join you, or form a small team of two of each discipline. I assume you are Process like me.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[zdas04]

The credible scenarios are the responsibility of someone with knowledge of the process. Maybe the process engineer?

Defining the required flow rate for each credible scenario is the responsibility of someone with knowledge of the process. Maybe the process engineer?

With a list of credible scenarios and an assigned flow rate for each, picking the controlling case requires considerable knowledge of the process conditions. That one might go to the process engineer as well.

Picking a valve to satisfy the flow rate of the controlling credible scenario is just arithmetic so nearly anyone who knows the difference between an SCF/day and a mole/hr. I think this bit of math goes to the process engineer as well since most instrumentation engineers think a mole is a furry critter or a dark colored spot on your skin.

Now we have a defined pressure, fluid, flow rate, and orifice size. At that point it is reasonable to pass the project off to I&E.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[Duwe6]

I *starred* zdas04's post, BUT there is a small quibble:

"Picking a valve to satisfy the flow rate of the controlling credible scenario is just arithmetic. . . "
Your arithmetic [as a Process/ I&E eng] is just to approximate the valve body size and orifice area. Then you give the conditions of the Controling Scenario and the approximate operating temperature of the bonnet of the PRV to a certified PRV shop. They will match a PRV and orifice area based on 'real' data from flow-bench testing that specific PRV.

Most calc's are 'on the money', but there are times when the minimum required orifice is smaller that what my calc suggested. PRV calc's get you close, but let the PRV mfr take your fluid mix, temperature and minimum flow rate and match it to their test data on their valves. That date has been verified by ASME [assuming the PRV is "V"-stamped]. Then using your projected bonnet temperature, they can give you the CDTP - Cold Differential Test Pressure - for that PRV [since they now know what spring will be used to build that PRV].

 

[Drexl]

Process

 

[SNORGY]

Basis (governing case), sizing (orifice) and scenarios are all attributable to Process. However, the Instrumentation Engineer would need to back-check the sizing calculations based on the revised K-factors for valves under consideration (if bids received ) or being purchased to make sure that the actual valve purchased is still correct.

 

[Latexman]

It depends on company work process. In my company the Process Engineer verifies and approves the PSV to be purchased. After construction, Process also verifies the PSV installation is in compliance with the PRD reoord or modifies the record to match a Code compliant installation.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[GHartmann]

I believe the rub is what is meant by sizing? Here is my view:

The process engineer sets the flow basis and set pressure based on a review of the protection criteria (fire, blocked flow, etc). Some would call that sizing; I would more specifically call it sizing basis.

That data then can be given to the instrument engineer who uses standard formulas to obtain the orifice size and proper valve.

In my work it was always a collaborative effort.

It also my opinion that a good process engineer could just as easily size the valve (calculate orifice size).

Many manufacturers have free software to size and pick the valves. They even have steps for all the cases which usually need to be documented for PSM purposes.