ESD 3

[Hamood101]

Hi all,

I got an engineering request to study the possibility to build a bypass around an ESD valve for maintenance purpose. Is it acceptable? I haven’t seen a bypass around ESD ! what is API or ASME reference in this case. ?

 

[TD2K]

I've seen bypasses around ESD valves to allow for maintenance and/or testing. Testing can also be accomplished with a partial stroke test.

The bypass can be a single valve or two valves. They are car sealed closed or lock closed since the ESD protection is lost if they were to be open. I've also seen limit switches installed on the bypass valves so an alarm sounds if the bypass valve is not in the closed position.

 

[BigInch]

Definitely a bad practice.
Practically speaking, smaller diameter bypasses are sometimes required for limited fuel flow to supply for black start purposes of the emergency power generator. Their use should be limited to those applications. A locking device and an electronic interlock, prohibiting start of the main process when the valve is open, should be contemplated.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[Hamood101]

Thanks to all.


But the bypass valve should be a manual isolation valve or another ESD i.e. we will have two ESD's in parallel !!

 

[BigInch]

Two ESD in parallel? Why? That won't increase reliability, where two ESDs in series would, and normally as TD2K has mentioned, a stroke test is sufficient to prove functionality. Do you really expect to do so many overhauls on one valve that you will need two, one as a spare when the other is removed for service. In that case I would spend more money and buy a proper ESD valve that will last and function when you need it to. Surely one good, proper ESD valve will be cheaper than buying two valves and putting them in paralled 100% spare service. Unless you have some very unusual requirements, I don't understand that logic.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[SNORGY]

You might consider parallel ESD valves or a bypass like Hamood101 suggests in certain instances, such as a requirement for buy-back gas from the pipeline line pack if you need it to start a compressor, for example. You might consider it also if you need provision for manual blowdown of a pipeline segment and you want to make use of vent or flare stack provisions on a lease immediately upstream of the primary ESD valve.

Any such scheme requires HAZID / HAZOP that includes thorough review against the governing Codes and local Regulations in force.

 

[BigInch]

Technically "parallel" configuration would imply the destination as well. What you describe Snorgy seems to be 2 ESD valves off the same line.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[SNORGY]

You are correct, BigInch.

In the examples I gave, I have typically forced opposite flow directions using check valves and directional ESDs.

Good point.

 

[SNORGY]

"Directional ESDs" meaning an ESDV that has a preferred flow direction through it.

 

[pmover]

I'm not aware of any references, just good sound engineering judgement and analysis. Remember, operations personnel will need to operate the system; hence, all the more reason to plan the design.

Additionally, ESD bypass valves, typically small diameter, are used to slowly pressurize the piping system after and ESD event has occurred. Opening a large diameter ESD block valves MAY not allow for a "controlled" pipe system pressurization. Hence, the reason for smaller diameter valves; typically, 2 small diameter manually operated valves in series.

For example, maintenance work is done in plant inlet filters, scrubbers, other equipment, etc. Once the work is completed, the plant is slowly pressurized in a controlled fashion using the smaller diameter valves. This method allows for examining the maintenance work, e.g. closures, flanges, threaded connections, etc. at various increasing pressures. The objective is to examine the piping system or maintenance work for leaks. IF leaks are found at lower pressures, then the gas loss (if needed) is minimal or perhaps repair measures can be made without depressurizing the entire piping system.

Once the piping system is fully pressurized to upstream valve pressures, then the ESD block valves can be fully opened. Then securely close, LOTO!, the smaller diameter valves, which will allow the ESD system to operate as designed.

hope this helps and good luck!
-pmover

 

[unclesyd]

We have two processes that use ESDs
The largest is a process where air oxidize cyclohexane in 6 100,000 gal reactors. A device similar to the one in link is used to allow a partial stroke test. We don't allow any bypass around the ESD in this process.

The second process is the oxidation of an alcohol with concentrated HNO3. If the reaction takes a wrong turn we have what we call dump valves, essentially an ESD, that dump the process material while adding water. We have parallel valves where one is always in the line at all times. We also have parallel relief valves on a 3-way valve that insures one relief valve on line at all time. This is strictly for maintenance of the valve.

 

[BigInch]

Unclesyd,
"essentially an ESD, that dump the process" is essentially a "relief valve".
"Emergency Shut down" normally implies that the fluid comes to a halt somewhere.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[unclesyd]

I realized that there maybe a little play with nomenclature on our part , but this a legacy system and were called ESD valves and or dump valves on PID. Pressure is the driving force in a runaway reaction, resulting in an increase in temperature. At around 130°C the material detonates. The process operates at 120°C In conjunction with these valves we cut off the HNO3, process air, and recycle NOX. One other thing is there is only 3 6" relief valves on this process after HNO3 is introduced. The reason is that a standard relief valve will not open fast enough so the pressure is maintained on the system. On several excursions we have put the relief valves in orbit, stub in and all. You don't want to be in this area when you have what we call a "running dump". The operation has vastly improved since the advent of electronic control.
This process is esentially a rocket engine in bottle, 65% HNO3 oxidizing Cyclohexanol.

 

[BigInch]

Just the names of that stuff are scarey. Sounds like X-15 fuel.

Although I have used snap-acting ball valves tied to a surge line for "relief purposes", we often use a special relief valve, a rather large throated device with a big needle cone configured for direct axial movement and plugging/unplugging the throat, for dumping large quantities of gasoline, etc. off a pipeline very quickly during a surge event. Kind of like swallowing a conical bronze point spear. In fact it happens to be called an "axial flow surge relief valve".

Where can I get some of that HNO3-Cyclohexanol? Does it come in 200 proof?

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[unclesyd]

Yes and under the right condition it probably measure at little higher.

The making of Nylon itself fraught with hazards.
A process upset can result in production of PIcric Acid that ends up in bottom of our storage tanks.
The Therminol will detonate at 927°F. This has occurred twice.
Nylon itself will rupture a 1" .376" tube if heated slightly above it's melt temperature. Might be able to get a picture of the last excursion.

 

[BigInch]

I have more respect for nylon.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[unclesyd]

BigInch,
Here is picture of a ruptured pigtail off a 16 position manifold that was running slow so there was an attempt to slightly warm the pipe. The pressure at this point is around 900 psig @ 285°C. This failure is a little different in that you can see the Nylon Polymer. In lines that are @ 2000 psig you don't see any polymer in rupture area and a very small, if any shear lip. There were around 5-7 mechanics and myself within 6' foot of this rupture. My ears rang for a couple of days.

The following doesn't really come under ESD but can defray the cost of a costly overhaul, $150,000. The continuous process is like a rocket ship, when you push the go button you are committed. If the polymer flow stops any where in the process, or the loss of steam or Therinol, or any utility you have about 30 minutes on the outside to get the process moving forward. A colleague and myself came up with a way to get another 15 or son minutes before the system solidifies. There are 3-4 jacketed tubular reactors 20" in dia. x 20' long. That noramlly operate at 250 Psig @ 208°C-243°C to remove water. As an emergency measures we tried raising the pressure to 275 psig and cut the heat to slow the boil off. It worked and gave us another 15 minutes on the clock.

 

[unclesyd]

Hope this turns out better than the last attempt. This not one of my photographs.

 

[BigInch]

Must have been one hellova bang.
I $%&^&%^ when a relief valve goes off.
You guys were lucky it was nylon inside.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[reihane1]

I have seen parallel ESD valves. it is for start up and it depends on size of the main ESD valve. for example we do not use by pass for valve size below 4 inches.some times we use manual valve un bypass line instead of parallel ESD valve.the size of bypass line is smaller and usually two valve one ball and one globe shall be installed on it