Calculating Pressure in Tank Manifold

[MechEng176]

I have a pipeline operating at 500psi and 60m3/min. I’m connecting 3’’ frac iron (good till 12,000psi) to the mainline to draw oil from it. The iron connects to an 8’’ manifold which connects to 4x 400bbl frac tanks. This tank manifold is only rated for 120psi and all the tanks are open to atm. Will the 8’’ manifold get overpressured from the mainline pressure?

I’m thinking that I'll only see head pressure from the tanks and friction pressure in the manifold… but I’m also a new grad…



Thanks,

 

[MechEng176]

Correction 60m3/HR so 1m3/MIN.

 

[LittleInch]

How is the pressure from 500 psi to atmospheric being controlled?

what is your presusre portection on the 120 psi manifold?

This is a wholly bad idea as you cannot know for certain that no one or even mechanical failure will block your line from the manifold to the tanks? If someone fell asleep and your rather puny sized tanks comapred to the flow rate over flowed then the first thing would be to shut the tank valve or the nearest one they could find. At that point, or very shortly after, your operating presusre, which could be quite low, will shoot up to 500 psi and you will have an even bigger disaster on your hands.

DO NOT connect lower presusre pipe work to higher presusre pipework without consiedering all posisble options and having at least two means of ensuring that your lower pressure pipwork cannot be over pressurised ( one of them normally being full flow relief valves). You might get away with it for a while, but sooner or later it won't work and then neither will you for quite a while.

I hope someone is checking your designs before you put htem into practice.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[MechEng176]

I kinda really oversimplified what we are doing.

The 500psi mainline is actually connected to a metering skid which is rated at PN100/600#. The metering skid has a flow meter which we can set to a certain flow rate and valves upstream of it will open/close accordingly.

This metering skid is then connected to the 105MPa rated frac iron which is connected to the 120psi rated tank manifold. This manifold has valves to each individual tank and they will all be open. Once the tanks reach 80% full we will close the valve on the mainline connecting the pipe to the metering skid, then another one right downstream of it. We won't be closing the tanks valves so no over pressure due to that.

Since the product is just flowing from the mainline, through the skid, through the hard pipe, through the tank manifold to the tanks (open to atm). I figured the only pressure on the manifold will be head pressure since the iron is 3'' and the tank manifold is 8''.

There isn't really any pressure protection on the 120psi tank manifold. All of it is contained in a berm though. This is a 1 day thing and I will be operating the controller and valves and other people will tell me when the tanks are full (10m away from me).

 

[LittleInch]

I have a philosophy that says you never call anything "temporary" as it encourages design like this. This is and remains a bad idea and the issue is that how do you know it won't happen again or become a standard operation even if just for "one day"?

If you're insistent on going ahead then you need to ensure that the tank valves can't be closed by either removing the handles or better still locking them open with the keys held by you or whoever is in charge.

You should INSIST that the manifold has pressure protection as this is the correct way to do things. Where you can take your relief line I don't know but you need to find somewhere

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

Absolutely LittleInch.

A safe design requires an isolation valve for separation from, and another device, pressure relief valve, or burst disk, for positive overpressure protection of the lower pressure piping!

Independent events are seldomly independent.

 

[MechEng176]

Thanks for all the input. I've decided to make a manifold out of XS pipe to keep from adding a full flow PSV to the 120psi rated manifold.

Regards,

 

[LittleInch]

Great - You'll sleep better at night.

Now you just need to make all the valves (tank and manifold) equal to the same rating (500 psig), i.e. class 300 minimum.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way