Requirement of Manual Ball valve between ESDV and MOV in Pig trap area 1

[Lawry1183]

We have a 20" fuel gas pipeline designed as per ASME B31.8 with permanent pig traps. We have the PID which is indicated below. I would like to get technical insight on the requirement of this valve.

Second query on same PID - Also as per Design engineering practice for pipelines, " use of fittings between isolation valves, such as flanges and instrument taps shall be avoided". Does this means SDV shall be welded type rather than flanged?

 

[LittleInch]

Oh holy mother of god. Who has designed this monstrosity?

Clearly someone who works for a valve company or is getting a cut of their profits.

For one thing, you normally try and avoid anchor blocks if you at all can - they are the work of the devil.

They why are there three valves on the incoming line? You only need on welded ESD valve and that's it.

Is this class 900? Your LL of 100 bar is pretty high for a Fuel gas line.

The usual rule is that the first valve or the first connection on the pipeline side is fully welded and after that most people flange them.

A DEP sounds like a shell spec. I would have to see the whole section to understand that phrase listed as it doesn't sound right to me.

 

[Lawry1183]

Oh holy mother of god. Who has designed this monstrosity?

Clearly someone who works for a valve company or is getting a cut of their profits.

For one thing, you normally try and avoid anchor blocks if you at all can - they are the work of the devil.

They why are there three valves on the incoming line? You only need on welded ESD valve and that's it.

Is this class 900? Your LL of 100 bar is pretty high for a Fuel gas line.

The usual rule is that the first valve or the first connection on the pipeline side is fully welded and after that most people flange them.

A DEP sounds like a shell spec. I would have to see the whole section to understand that phrase listed as it doesn't sound right to me.

Thank you @LittleInch..
Yes, it seems a lot of valve. That's the reason got perplexed by this arrangement.

We have reviewed the stress report and anchor block has been mitigated.

As per operations they require the esdv to be flanged to facilitate maintenance eventhough it's top entry design. Hence the consultant provided a welded mov and then flanged esdv so that when esdv taken for maintenance still the pipeline can be isolated with mov.

However,the requirement of the manual valve between the esdv and mov is still a mystery.

Yes the DEP is shell DEP for pig traps.

 

[georgeverghese]

They want DBB upstream of the critical ESDV so that the ESDV can be safely removed without having to depressure the entire upstream pipeline. Otherwise, the Plant Owner may be forced to consider risky alternatives, of which there are many. But I dont see an intermediate bleed.
The DN500 MOV is a nice feature to have in case the ESDV is leaking upon emergency shutdown - operator can close this MOV from remote at control room if required. But where is the open - close pushbutton tag for the MOV?

 

[LittleInch]

Oh no, not that old chestnut about "but we need to be able to do maintenence on it".

Next time ask them how many times in the last 25 years have they ever had to either do any maintenece on a valve like that needing it to be removed or at all. Then wait for the silence. And why would they ever need to do anything to a valve which never closes other than twice a year to test it?

The probability that anyone will ever remove that ESD valve is minute. If they ever do then there are many ways to seal off the incoming line or just do it at the same time as you blow the line down for some other reason or when the plant is on turnaround.

ESD welded in valves on the entry into a terminal are a good idea. Adding in extra isolation valves is not. Basically where do you end?
Every valve is a potential leak path.
Those valves are there for catastrophic damage and shut off of most of the incoming supply. They do not need to be bubble tight.

Personally I've told the ops team to get real and it's for them to justify the $2M+ for something they will almost certainly never have to use. Again, expect silence.