That was a choice made at the time the automation was set up. Usually that particular choice gets made during a HazOp when someone proposes an outrageous scenario, and the team shifts focus to protecting against the one-in-a-billion possiblity of that occurance for the rest of the HazOp. I've seen it happen many times and it would make me laugh if it wasn't so sad.
I've never set up a compressor to blow down on a trip. I've been involved in situations where recips were belown down on an ESD when the ESD strategy is to blow the entire station down on ESD, but that strategy is not universal.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
If there is a process description for the system the reason might be discussed in there also.
You can also propose that it be changed after looking into the what effects the change would have and go through your MOC (management of change) procedure. Documentation such as cause and effects, procedures, training would have to be updated, basically any designated key documents that would need to be updated.
It's as near as universal can get and I wouldn't recommend changing it.
How about this one,
BECAUSE IF YOU DON'T DO IT YOU ARE VIOLATING FEDERAL LAW!
CFR 192.167
And see API RP14C
Recommended Practice fo Analysis, Design, Installation and Testing
of Basic Surface Safety Systems
for Offshore Production Platforms
Sheet 5 of 6 Page 83
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
Gas audibly leaked out at high pressure, drawing the attention of several men and triggering six gas alarms including the high level gas alarm. Before anyone could act, the gas ignited and exploded, blowing through the firewall made up of 2.5 × 1.5 metre panels bolted together, which were not designed to withstand explosions. The custodian pressed the emergency stop button, closing huge valves in the sea lines and ceasing all oil and gas production.
Theoretically, the platform would then have been isolated from the flow of oil and gas and the fire contained. However, because the platform was originally built for oil, the firewalls were designed to resist fire rather than withstand explosions. The first explosion broke the firewall and dislodged panels around Module (B). One of the flying panels ruptured a small condensate pipe, creating another fire.
10:04 p.m. The control room was abandoned. Piper Alpha's design made no allowances for the destruction of the control room, and the platform's organisation disintegrated. No attempt was made to use loudspeakers or to order an evacuation.
Emergency procedures instructed personnel to make their way to lifeboat stations, but the fire prevented them from doing so. Instead the men moved to the fireproofed accommodation block beneath the helicopter deck to await further instructions. Wind, fire and smoke prevented helicopter landings and no further instructions were given, with smoke beginning to penetrate the personnel block.
As the crisis mounted, two men donned protective gear in an attempt to reach the diesel pumping machinery below decks and activate the firefighting system. They were never seen again.
The fire would have burnt out were it not being fed with oil from both Tartan and the Claymore platforms, the resulting back pressure forcing fresh fuel out of ruptured pipework on Piper, directly into the heart of the fire. The Claymore platform continued pumping until the second explosion because the manager had no permission from the Occidental control centre to shut down. Also, the connecting pipeline to Tartan continued to pump, as its manager had been directed by his superior. The reason for this procedure was the exorbitant cost of such a shut down. It would have taken several days to restart production after a stop, with substantial financial consequences.
Gas pipelines of both 16″ and 18″ diameter ran to Piper Alpha. Two years earlier Occidental management ordered a study, the results of which warned of the dangers of these gas lines. Due to their length and diameter, it would have taken several hours to reduce their pressure, so that it would not have been possible to fight a fire fueled by them. Although the management admitted how devastating a gas explosion would be, Claymore and Tartan were not switched off with the first emergency call.
10:20 p.m. Tartan's gas line (pressurised to 120 Atmospheres) melted and burst, releasing 15-30 tonnes of gas every second, which immediately ignited. From that moment on, the platform's destruction was assured.
10:30 p.m. The Tharos, a large semi-submersible fire fighting, rescue and accommodation vessel, drew alongside Piper Alpha. The Tharos used its water cannons where it could, but it was restricted, because the cannons were so powerful they would injure or kill anyone hit by the water.
10:50 p.m. The second gas line ruptured (the riser for the MCP-01 platform), ejecting millions of cubic feet of gas into the conflagration. Huge flames shot over 300 ft (90 m) in the air. The Tharos was driven off by the fearsome heat, which began to melt the surrounding machinery and steelwork. It was only after this second explosion that the Claymore platform stopped pumping oil. Personnel still left alive were either desperately sheltering in the scorched, smoke-filled accommodation block or leaping from the various deck levels, including the helideck, some 175 ft (50 m) into the North Sea. The explosion also killed two crewmen on a fast rescue boat launched from the standby vessel Sandhaven and the six Piper Alpha crewmen they had rescued from the water.[4]
11:20 p.m. The gas pipeline connecting Piper Alpha to the Claymore Platform burst.
11:50 p.m. The generation and utilities Module (D), which included the fireproofed accommodation block, slipped into the sea. The largest part of the platform followed it.
12:45 a.m., 7 July The entire platform had gone. Module (A) was all that remained of Piper Alpha.
At the time of the disaster 226 people were on the platform; 165 died and 61 survived.[10] Two men from the Standby Vessel Sandhaven were also killed.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
I see that, but irrelevant. It's a CFR and that's the law.
I personally do not know of ANY REGULATED compressor station that does not blow down on ESD, offshore, or onshore. Some unregulated, mini HP, field compressor, in some podunk gathering system, with a population of 12 cows, go for it. I like a good BBQ just as much as the next guy.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
I think the OP is confusing the issue by referring to "esd" in the title, but then talking about "trips" in his question, which apprently "always happens". So his trips are probably normal nuisance shutdowns, and not really ESD's. I don't know, but this thread is useless without him being aware of the importance of terminology and what it implies.
He said it always blows down after a trip. He didn't say that it always trips and blows down. The only hint he gives of multiple occurrences is the word "always", but that still could mean it only happened one time in his entire life.
Useless? USELESS? Well, being that the OP now knows that further actions may be potentially illegal, not to mention dangerous, I wouldn't say that the thread was entirely useless.
And we hopefully learned not to give what can be preceived as well founded advice, based on years of experience, on such sensitive topics, especially when the advisor isn't aware of the full details. IMO the best course of action in such cases is to convince them into leaving it alone completely and, or, recommend that he find somebody who is qualified to troubleshoot the system and rectify it properly, rather than in any way, shape or form, potentially encourage them to switch off what may be an essential safety system.
I wouldn't say that the thread is pointless, if the OP now realizes that acting without knowledge and some serious thought in this matter at hand could be a very, very bad idea and that we also learn to think of the consequences that our advice might bring especially when involving serious safety concerns. After all, this isn't a question about pressure loss of a micro psi or two going around some 2" elbow.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
Agreeed. There's never useless information provided by you, David or anyone here. I meant useless in terms of trying to accuralely answer, what appears to be, an ambigious, unclear question from the OP.
DLite30, you are correct. Please ignore any safety related issues. My query is purely technical: If i stop a recip compressor which compresses dew point gas, must it be depressurised?
For a centrifugal machine, it is acceptable to leave the machine pressurised then restart. I don't think this can be done in a recip and want to undertstand why.
Starting torque requirements are minimized when the machine is started in the unloaded condition. That is typically ensured by no pressure, or only suction pressure remains in the machine when it is shut down. Consequently, especially if suction pressure is minimal, there is little reason to keep even small amounts of potentially dangerous gas trapped inside a unit that is shut down and possibly a lot more reasons not to keep it.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
The only time we blowdown any of our recip units is for maintenance or a station ESD (emergency), or for the rare case like BigInch described where the starting torque is too much for the engine starters to handle, then we just do a partial blowdown and re-pressurized to line pressure after start-up.
Now, we're dealing with dry, pipeline quality gas, not gas that may have a fairly high dew point temperature, as it seems you have. With rich gas, I can only imagine a couple reasons why you would blow down upon each shutdown would to be to limit the amount of condensate build-up in the piping, bottles or cylinders, which could be, however unlikely, an issue on start-up (hydro-testing a cylinder). Or perhaps maybe to protect soft parts like o-rings, etc from degradation, but most materials used are pretty resistant to normal gas components. So, those would be my guesses as to why the compressor was set up to operate in that way. I would back-track the project to the automation guys, the project manager/engineer, to see what the reason for that may be (if those people are still around).
Control engineers, project manager. You forget that the engineers work for some other company and the project manager has no idea why they did anything, just how late and over budget the project was delivered.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
(a) Except for unattended field compressor stations of 1,000 horsepower (746 kilowatts) or less, each compressor station must have an emergency shutdown system that meets the following:
(1) It must be able to block gas out of the station and blow down the station piping.
It must be able to block gas and blow down, it is not mandatory that this happens automatically.!!!!
We have several recip compressors running in an onshore oil production/gas injection facility. The condition of starting up the compressors loaded or unloaded depends on the 1st stage suction/discharge pressure because of (as BigInch and DLite30 said) the starting torque requirements. Have a look to the compressor's operating manual. At any trip we blowdown the compressors to avoid condensation in the lines (wet gas). The amount of gas lost is negligible when compared to the problems we could have getting liquids inside the cylinder.
We have several recip compressors running in an onshore oil production/gas injection facility. The condition of starting up the compressors loaded or unloaded depends on the 1st stage suction/discharge pressure because of (as BigInch and DLite30 said) the starting torque requirements. Have a look to the compressor's operating manual. At any trip we blowdown the compressors to avoid condensation in the lines (wet gas). The amount of gas lost is negligible when compared to the problems we could have getting liquids inside the cylinder.
