5 replies to this topic

[moein_omg]

Dear all,

 

I am involved in a project of designing 10 crude oil multiphase offshore flowlines.

now, my question is what are the criterias that should be used to find the most appropriate pipeline diameter?

the procedure that I already followis: 1-nominateing three diameters. 2-performing simulation using pipesim software. 3-calculating parameters such as pressure drop, flow regime, liquid hold-up, gas and liquid velocities.

I also have already came across criterias

1-maximum velocities to inhibite errosion,

2-max velocity to acertain exstence of a ani-crrosion film

3-minmum velocity to minimize sluging

4-minimum liquid elocity to minimize deposition of solids and sand.

5-maximum pressure drop per length

 

which of the mentioned criteria shall be taken into consideration?

and also, is settlement of water a concern in design when accumulating in the bottom?

 

thanks in advance for help

 

[demank]

Dear Moein,

Since most flowlines operate at high pressure, pressure drop is usually not a governing criteria in selecting a diameter.

However, pressure drop may have to be considered for some long flowlines.

The a minimum flow velocities of 10 - 15 ft/sec should be maintained to keep liquids moving in the line and thus minimize slugging.

The maximum allowable velocity would be set by the minimum 60 ft/sec, 50 ft/sec if it is necessary to inhibit for CO2 corrosion, or the erosional velocity.

[moein_omg]

Thank Demank,

 

that is quite reseanabloe. What about flow regime? Is, in your openion the best pipeline diameter the lowest diameter that satisfy the mentioned velocity criteria. Another question: How can I calculate the mentioned velocity is it for liquid or gas or overal mixture?

 

Best Regards

[demank]

Hello,

About Flow Regime, mostly we avoid of the slug flow in horizontal line and slug & froth flow in vertical line, "although frequently we does not have the choice".

Slug flow may introduce a flowrate/pressure intermittency that cause a trouble to process control.

In some cases, slug flow may be avoided when we choose smaller pipe size that will result higher pressure drop.

In vertical upflow, oversizing pipesize will cause a bubble flow regime and a large liquid inventory, that may cause excessive hydrostatic pressure drop.

 

The mentioned velocity is a mixture velocity, not superficial velocity of gas/liquid.

[moein_omg]

thanks a lot

 

it really shaped my mind. do you have a reference for the mentioned velocity criteria. Is there any standard in this regard?

 

thanks again

[demank]

API RP14E (ISO 13703):

Minimum velocity in two-phase lines should be about 10 ft/s (3 m/s).

Maximum velocity is its erosional velocity.