Line Sizing

Line Sizing

Objective of Training

Learning the basic concept

for the determination of line size.

In determining line size, Process Engineer should recognize;

•What should be taken into account?•What is the background of sizing calculation?

What is Line Sizing?

To determine the size of piping

Why is Line Sizing Necessary?

To select appropriate size

If too large piping is selected,Not Economical!

If too small piping is selected,Hydraulic Problem!

In both cases, Not Good Design!

Who does perform Line Sizing?

Process Engineer

To perform Line Sizing, engineer has to know;Physical properties, State, Required flow rate,

Process requirement, etc.

It is Process Engineer who knows those things.

When is Line Sizing performed?

Early stage of project

Piping design, civil design, mechanical design will executed on the information of line size.

Size of piping should be fixed before detail design.

How is Line Sizing performed?

Based on Velocity and Friction Loss

Criteria from velocity and friction loss is prepared.Each company has their own criteria.

Contractor, Licensor, Plant Owner

Applicable criteria is different in case by case.Usually, “Line Sizing” that is software to calculate

friction loss and velocity is used.

How to Calculate Velocity?

A

wv

v; velocity [m/s]w; mass flow rate [kg/s]ρ; density of fluid [kg/m3]A; area of piping [m2]D; internal diameter of piping [m]

w

ρD

A=π(D/2)2

How to Calculate Friction Loss?

Incompressible Fluid (single phase)Fanning’s Equation

ρD

LvfP

24

2

ΔP: friction Loss [Pa]f: friction Factor [-]v: velocity [m/s]L: pipe Length [m]ρ: density of fluid [kg/m3]D: Internal Diameter of Piping [m]

How to Calculate Friction Loss?

What is Incompressible Fluid? Liquid Gas if the following are satisfied,

• Velocity is less than 61m/s

• Pressure loss of system is less than 10% of entrance pressure

For gas, If the pressure drop is greater than 10%, the pipe can be divided into shorter sections and calculated for each section, or exact calculations based on compressible flow theory must be made.

How to Calculate Friction Loss?

Friction Factor For laminar flow (Reinolds Number < 2100)

Re

16f

f; friction factorRe; Reinolds Number [-]Re=ρvD/μμ; viscosity of fluid [Pa ・ s]

For turbulent flow (Reinolds Number > 2100)Empirical equation or chart is used.

Friction factor is the function of pipe diameter (D) and relative roughness of piping surface (ε). Unit of ε is length. For carbon steel: 0.04572mm, For stainless steel: 0.0015mm

How to Calculate Friction Loss?

Effect of Flow Rate and Diameter of Piping on Friction Loss

A: Area of Piping (m2)Q: Volumetric Flow Rate (m3/s)2

2

2

4

2D

Q

D

Q

A

Qv

52

22

2

164

24

D

LQf

D

LvfP

ρ

Frication Loss is;inverse proportional to the 5th power of diameterproportional to the 2nd power of flow rate

How to Calculate Friction Loss?

Compressible fluid (single phase)

Example for compressible service Flare System Gas Pipe Line

How to Calculate Friction Loss?

Two-phase flow (Gas-Liquid)Flow pattern and erosion velocity need to be taken into

account.Depending on gas velocity and liquid velocity, flow pattern

varies. Some kind of them cause vibration of piping. Therefore, such flow pattern should be avoided if possible.

Erosion by kinetic energy of fluid could occur if velocity is too high. Erosion velocity is the guideline predicting limit. Velocity should be less than erosion velocity.

Pipe Materials and Sizes

Materials used depends on the applicationThe required thickness of a pipe is proportional

to the pressure the pipe must carry. However, not all pipes operate at high pressure. Therefore, pipes may be available in different wall thickness (schedules).

There are many different standards governing pipe diameter and wall thickness. A manufacturing specification and class or category are usually needed to completely specify pipe dimensions.

Minor Losses

Friction losses also result from fittings in the line, changes in direction, and changes in flow area. These losses are known as minor losses. Two methods are used to calculate minor losses:

Equivalent Length Loss Coefficient

Equivalent Length

Each fitting or other flow variation is assumed to produce friction equal to the pipe wall friction from an equivalent length of pipe. The equivalent length for all minor losses are added to the pipe length term, L, in the Fanning equation.

Ltotal = L + ∑Le

Bernoulli Equation

Bernoulli equation is an energy conservation equation.

E1 = E2 ＋ Ef

E1: Energy at point 1

E2: Energy at point 2

Ef: Energy Loss by friction

Fluid Energy

Kinetic Energy: Ev = v2/2Potential Energy: Ez = zgPressure Energy: Ep = p/ρTotal Fluid Energy = Ev + Ez + Ep

v: velocity [m/s] z: elevation [m] p: pressure [Pa]ρ: density [kg/m3] E: energy [J/kg]

Energy Balance

1 2

Ef

E2E1

E1 = E2 + Ef

Reference

These are the example of general reference books. You can find similar ones in book store, of course. To get further understanding, it is recommended to have it.

Perry’s Chemical Engineer Handbook