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Nitrogen Displacement

Calculations and Procedure

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Introduction

The Nitrogen displacement is a common practice in the pipeline contest. It consist in connecting a nitrogen pumper to the pipeline and use the gas pressure to push the product to the receiving depot. Generally, it is used a “pig” to separate the nitrogen from the product.

The procedure permits:• To clean the pipeline;• To remove all the products from the pipeline;• To inert all the pipeline and prepare it for maintenance works.

The most relevant risk of the nitrogen displacement are:• High pressure in the line (generally above the operating pressures);• Possible introduction of nitrogen to the receiving tank;• High velocity of the “pig”, that could compromise its integrity and cause potential

waterhammer.

To avoid all the risks and optimize all the parameters it is essential to study carefully the alignment and the process to be performed.

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What do we do

Streamline Engineering is able to provide the calculations and the procedures about the following activities: • Pig positioning along the line for partial displacement;• Displacement procedure and calculations;• Vent and flushing operations;• Re-filling procedure and calculations.

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Preliminary Analysis

The first step concerns the study of the following data:

• Profile characteristic (elevation vs length);

• Mechanical characteristics of the Pipeline:• Material, Diameter and Thickness;• Radius of curvature;• MAOP/DP;

• Number and types of valves along the line;

• Definition of the valves’ CV;

• P&ID analysis;

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Hydraulic Calculations

The process hydraulic calculations allow to define:

• Hydraulic grade line at the different flowrate;• Nitrogen volume required; • Nitrogen flowrate and pressure; • Liquid flowrate to control at the receiving station; • Pressure along the line and at the receiving station;• Control point for the pig tracking;• Multiphase simulation in LEDA FLOW.

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Progressiva [km]

Geodetica Gradiente Idraulico [m]; Gasolio ; Densità @ 15°C 846 [kg/m 3̂]; Viscosità Media 5.3 [cSt]; Portata 200 [m^3/h]; DR Factor % 0

Maximum Allowable Operating Pressure (MAOP) [m] piezom N2 ideale1

Press N2 ideale1 Press N2 eff 1

Piezom N2 eff 1 Pressione Massima

V13TER II VALVOLA V 18

VALVOLA V 17 VALVOLA V 16

VALVOLA V 15 TER VALVOLA V 15 BIS

VALVOLA V 15 VALVOLA V 14

Fine spiazzamento Volume tot N2 tratto 1

Volu

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o [S

m3 ]

Alte

zza

[m]

PC-1

Q chi = 200 m3/hQN2 = 2700 Sm3/h

T = 1 h - 15 min

PC-2 PC-3 PC-4

Q chi = 200 m3/hQN2 = 1500 Sm3/h

T = 2 h - 0 min

Q chi = 200 m3/hQN2 = 0 Sm3/h T = 1 h - 0 min

PC-5 PC-6

00.511.522.533.544.555.566.577.588.599.51010.51111.51212.51313.51414.51515.51616.51717.51818.51919.52020.52121.52222.52323.52424.525

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Pres

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arg]

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zze

[m]

Progressiva [km]

[m] Geodetica Gradiente Idraulico [m]; Gasolio ; Densità @ 15°C 846 [kg/m 3̂]; Viscosità Media 5.3 [cSt]; Portata 200 [m^3/h]; DR Factor % 0

Maximum Allowable Operating Pressure (MAOP) [m] V13TER II

VALVOLA V 14 VALVOLA V 15

VALVOLA V 15 BIS VALVOLA V 15 TER

VALVOLA V 16 VALVOLA V 17

VALVOLA V 18 Chivasso

Press N2 eff 1 [bar] Fine spiazzamento

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Documentation and Field Activities

Streamline Engineering provide the following documentations to the Customers:• Detailed procedure of the displacement operations consisting of, at least:

• IInitial conditions and alignment of the pipeline and plants;• Specification of the PIG;• Pumper and nitrogen tank design in terms of volumes and flowrates;• Safety equipment verification.

• Schedule of the pig movement along the pipeline. List of the action to be carried at each control point;

• Supervision on field during the displacement activities.