6 replies to this topic

[Albator83]

Good day all,

I am trying to understand what would be the thinking process of a process engineer to decide on what the valves might be?

For example in Semi conductor industry, high purity is required. This is the first stage of the questioning : High Purity Yes/No.

Then I understand it is about Pressure..then perhaps flow control?  they may decide on Butterfly, Diaphragm..or are there any 2 or 3 more key questions to ask to narrow down to the type of valves?

I try to build the tree of decision making and the appropriate valve. SOmetimes, different type of valves may fit the bill, and its good because i also want to understand when one valve can substitute an other. 

 

High Purity Yes/ No. If Yes, what pressure. Then what is flow control requirement? If between XX and YY pressure and high flow control, , then either valve Type A, B or C

If between YY and ZZ then Type C or D...

 

Does this make sense?

 

Regards

Rach

Edited by Albator83, 07 June 2022 - 11:59 PM.

[Pilesar]

Purity is the key. Once you eliminate valves with metal to metal contact then it narrows the choices. Depending on the service requirement other specifications can be used to eliminate choices. In the end, there will still be more than one reasonable choice so the final selection becomes more subjective including delivery time, cost, part availability, vendor relationship, previous experience, etc.

[Albator83]

Thanks Pilesar, I am trying to trigger conversatins with stakeholders based on the " final selection becomes more subjective". I want to see how we could direct users to the lowest Total cost of ownership option for the situation.

[Art Montemayor]

As a process engineer, you are responsible - in my opinion - for the safety, operability, and durability of the valves (control, block, or otherwise) used and specified for the process.   Whether the valve is "cost effective" is a subject that the Project Manager together with his design team and purchasing personnel discuss, debate, and agree on.  That's the way I've handled projects. 

 

The main process document that helps to determine what kind of valve is required is the P&ID - something you haven't mentioned and which is the full, technical description of the process where the valve is applied.  A control valve is considered an instrument by me; therefore instrumentation engineers participating in the design should play a role in its final specification - and application.

 

Cost effectiveness is important; but it isn't the most important criteria in a process design - particularly when a hazardous or new process is involved.  A project manager or leader has to be involved - or someone ultimately responsible or accountable for the final design and specifications.

 

That has been my experience.

[Albator83]

Art Montemayor,

i could not agree more. just to clarify, if the P&ID says use butterfly valve, the process engineer will never replace it by anything else, so working on possible substitution does not make sense?

 

regards

 

Rach

[Pilesar]

Sometimes valve symbols are chosen for a P&ID somewhat arbitrarily. Another type of valve may be suitable. The process engineer and the instrument engineer should communicate. P&IDs are Process and Instrumentation drawings so both engineers should be involved in their development. Both need to understand the reasons for the design selection. I think of the instrument engineer as disadvantaged because there are things the process engineer intends that are not transferred in writing to the instrument engineer. Communication is key. Better choices may be made after combining information.

[Art Montemayor]

I am glad we agree on the basic principles of process design and how it is applied to a P&ID.

 

However, although a P&ID is a sacred document that should be guarded by process operators, it is always subject to revisions and challenges - especially by plant process operators and engineers.  I have never seen a P&ID in an operating plant that wasn't revised at one time or another.  In your specific case, I would use the ability to question and challenge the use of an installed butterfly valve if it is found or thought to be a potential cause for safety, product specifications, or operator operation.  If there is serious concern for its application, then by all means generate a meeting between process, instrumentation and operational individuals and reach a logical and practical decision as to its use.