Explanation for nitrogen filling of vessel 2

[PI055]

I was checking the thread794-326793 which is closed so I start a new one with similar subject. I need to prepare the procedure for the filling of one drain vessel and one pig launcher/receiver with nitrogen for conservation purpose. These vessels are part of pipeline and need to be protected because that part of pipeline shall be not used in a next 4-5 years. As my assumption, I guess that vessel have to be isolated from the rest of pipeline, all openings closed, then use one nozzle to introduce nitrogen inside and leave one vent open until all air is replaced with nitrogen. After that all nozzles shall be closed. Can anyone tell me if I'm on the right track and also explain me some details from practice (e.g. which tools do I need, how to know when all air is out etc.)?

 

[LittleInch]

key issue is what design pressure is your tank? The pig receiver will be fine - just flush through say 2-3 volumes of the trap at atmospheric pressure and then pressurise to sat 3 barg. Then hang notices everywhere saying it is nitrogen filled under pressure. Do not vent without proper procedure in place.

But drain vessels ar eoften only atmospheric pressure vessels and so you can't pressurise the and also need to allow the normal air pressure to vary without damaging the tank or allowing air to breahte in and out.

You might be better just flushing it with Nitrogen to get the vapour dry and then fitting a desiccant breather and replacing the dessicant every now and then.
..
Or dangling a couple of bags of desiccant into the tank.

It's really the water vapour you're removing although lack of Oxygen reduces corrosion as well.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

Typically it goes something like this.
Rinse, wash, and flush clean.
Purge with nitrogen until the oxygen and moisture readings are low enough.
If the system can be pressurized, then fill to the pressure, close all valves, and set your alarm to notify if pressure drops.
If the system cannot handle much pressure, or the swings with temperature can be problematic then supply nitrogen at just above atmosphere.
This must be a continuous supply of nitrogen with alarms on your supply to prevent running out.
As a backup there should be plenty of desiccant packs inside the system and a desiccant breather on your emergency vent.


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P.E. Metallurgy, consulting work welcomed

 

[PI055]

LittleInch & EdStainless thank you for reply. I have almost none experience outside the office, so can you explain me which device is used for checking if oxygen is removed and what is desiccant breather ?

 

[KevinNZ]

Way not pull a vacuum then fill with N2?

 

[crshears]

Depends on if vessel can withstand vacuum . . .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[MJCronin]

.... a Star for EdStainless, who is always on the money, IMHO ...!!!

To elaborate on his points:

- There is nothing to prevent you from using a dessicant AND a Nitrogen purge .... Dessicants are cheap, but require opening the system to find out if they are still working. They are, IMHO a back-up if the nitrogen pad system fails

- A nitrogen "padded" system is the most commonly used solution to this situation. The nitrogen padded system should incorporate pressure gauges and an alarm if the pressure drops off some predetermined level

- If the system is to be used only every 4-5 years, there should be a written proceedure to periodically check on its status and verify the nitrogen pad. Perhaps a yearly/six month check would be reasonable

- Your goal is to eliminate water and oxygen thereby preventing corrosion

There is much information out on the interwebs about nitrogen padding of tanks .... but, your question is unique because it is not about "leaky" tanks and is about very long term padding of a pipeine

PI055:

You state: "I have almost none experience outside the office, so can you explain me which device is used for checking if oxygen is removed and what is desiccant breather ?"

Were you assigned to design this complex and expensive system by an MBA ?

My opinion only ....

MJCronin
Sr. Process Engineer

 

[SnTMan]

Well, yeah, the MBA couldn't do it

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[EdStainless]

You can buy or rent oxygen/humidity meters. These are special as they measure way below atmospheric values (say down ppm oxygen and Dew Points of -40).
Any system that is closed up will warm during the days and cool at night. As it warms the gas inside expands, and when it cools it contracts. If you don't have it extremely well sealed it will vent a little gas every day and try to suck in air (with oxygen and moisture) at night. There needs to be a vent so that if the internal nitrogen is ever lost the system can breathe, but you want to be sure that as it sucks in air that air is at least dried. So a vent with internal desiccates is used.
Yes the additional desiccant inside the system is also a backup to your nitrogen pad.
I have seen such systems on 3mo or 6mo inspection schedules depending on the reliability and size of the nitrogen source.
There need to be written procedures for all of this.

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P.E. Metallurgy, consulting work welcomed

 

[r6155]

Paint can be an alternative for surface protection and avoid Nitrogen pressure.

Regards

 

[PI055]

Well thank you all to the answers. I was temporary assigned to this task, but now my colleague takes over and he knows exactly what to do.

 

[GD2]

Is the underground drain tank UL-58 or 1316? These tanks are tested with positive pressures. Check the size of the tank to determine the hydro test pressure and then set the positive pressure for the nitrogen purge.
Once you have determined the tank purging pressure, you can purge the whole pig station at the same pressure (say at 1 psig).

GDD
Canada

 

[MJCronin]

BWHAHAHAHA !!!!

I guessed that there was some type of MBA/incompetent running this project !!!... and now the OP posts:

Well thank you all to the answers. I was temporary assigned to this task, but now my colleague takes over and he knows exactly what to do.

More Proof Positive of incremental engineering management sabotage !!!

.... always remember, on the backside of any MBA graduate certificate are the words:

"Anybody can perform any task in any amount of time"

MJCronin
Sr. Process Engineer

 

[LittleInch]

MJC. I've missed you the last few days. Have you been ill?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.