ESD
ESD
(OP)
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. ?
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. ?





RE: ESD
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.
RE: ESD
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.
RE: ESD
But the bypass valve should be a manual isolation valve or another ESD i.e. we will have two ESD's in parallel !!
RE: ESD
If it ain't broke, don't fix it. If it's not safe ... make it that way.
RE: ESD
Any such scheme requires HAZID / HAZOP that includes thorough review against the governing Codes and local Regulations in force.
RE: ESD
If it ain't broke, don't fix it. If it's not safe ... make it that way.
RE: ESD
In the examples I gave, I have typically forced opposite flow directions using check valves and directional ESDs.
Good point.
RE: ESD
RE: ESD
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
RE: ESD
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.
RE: ESD
"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.
RE: ESD
This process is esentially a rocket engine in bottle, 65% HNO3 oxidizing Cyclohexanol.
RE: ESD
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.
RE: ESD
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.
RE: ESD
If it ain't broke, don't fix it. If it's not safe ... make it that way.
RE: ESD
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.
RE: ESD
RE: ESD
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.
RE: ESD
RE: ESD
RE: ESD