Line Sizing Calculation With Example is the key focus of this article. Line sizing calculations are very important from a process engineering standpoint. Almost all types of industries have different types of pipelines, such as those for tap water, demineralized water, cooling water, chilling brine, chemical transport, air, steam, and oil.
So, in today’s article, I will cover all the important aspects necessary to understand the significance of line sizing, clarify its importance, and calculate the required line size.
My name is B A Kadam, and I have 15 years of experience as a process engineer and project engineer in the chemical and oil and gas industry. I will do my best to clarify line sizing concepts and explain the topics using all my experience.
To understand line sizing calculations, I have divided this topic into several key sections: what line sizing is and why it is important, key factors in line sizing, category of line sizing, erosional velocity, data required for line sizing calculations, a step-by-step procedure, examples, relevant standards, tools and software for line sizing, online calculators for liquid line sizing, and an Excel sheet. I will conclude with frequently asked questions about line sizing.
I have given many interviews in my early career, and I am currently taking interviews frequently for process engineering positions. I will try to cover the questions that are very important for line sizing, which will help you get selected. Additionally, I will provide interview tips that will assist you.
Table of Contents
What is line sizing, and why is it important?
What is Line sizing?
In simple terms, line sizing is a step-by-step procedure that helps calculate the required diameter of a pipe according to the process requirements.
Importance of Line sizing
Line sizing is very important for several reasons, as outlined below.
- Efficiency: Proper line sizing ensures that the required flow and pressure are maintained.
- Safety: Proper line sizing is crucial for safety. Incorrect line sizing can result in chemical leaks, which can be hazardous. Additionally, if we do not consider right pressure , it will lead to the release of pressure from the line to outside which may be danger for human as well as asset.
- Cost: Cost is a key factor in all industry. Wrong line sizing will cause to high capital expenditures (CAPEX) and operational expenditures (OPEX).
- Piping Life: Proper line sizing contributes to extending the lifespan of the pipe
Key Factors in Line sizing Calculation
There are many factors that are important for line sizing. The following are the main key factors I have shared based on my knowledge and experience. You can suggest additional factors based on what you know. Please comment, and I will update this section with your name as a reference.
Flow Rate
Not only from my experience but also from common sense, the first important thing that comes to mind when we think about line sizing is flow. We need to consider the amount of flow to determine the line size. If the flow changes, the line size will also change. Generally, we use cubic meters per second (m³/s) as the unit for flow.
In flow rate we have to chose as like normal flow rate and design flow rate.
Fluid Properties
In fluid properties, we need to consider density, viscosity, and the state of the fluid, whether it is gas or liquid. Density is important because if it changes, the volume will also change. Viscosity is important because if it changes, the resistance to flow will change.
Velocity
Velocity is very important because changes in velocity affect the flow rate and pressure conditions. We need to consider both minimum and maximum velocities. Minimum velocity can lead to higher costs, while maximum velocity depends on erosional velocity.
Allowable Pressure drop
Allowable pressure drops are important for getting the right design. From what I understand, two key factors for line sizing are velocity and allowable pressure drop, and both are connected. If we increase the velocity, the pressure drop will also increase.
Pipe Properties
As the properties of the fluid are important, the properties of the pipe are also very important. For pipe properties, we need to consider the schedule number and the material of construction. The schedule number affects the pipe thickness, and the material of the pipe affects the roughness factor.
In addition to these, several other factors like temperature, environmental conditions, and industry standards are also important. However, I have considered the above as key factors based on my knowledge.
Category of line sizing Calculation
There are two main categories of line sizing: compressible fluid line sizing and non-compressible fluid line sizing.
Compressible Fluids
These types of fluids change density when pressure changes, which affects line sizing. As discussed earlier in the key factors, we first need to calculate the density based on the given flow, temperature, and pressure. We can use the simplified ideal gas equation to calculate density.
Non-Compressible Fluids
In this case, the density does not change with pressure. This makes the process simpler. Later, we will cover an example of this to help you understand non-compressible line sizing.
Erosional velocity
Erosional velocity is the minimum velocity that prevents solid particles in the fluid from impacting the pipe, helping to avoid erosion.
When selecting the velocity, the minimum value depends on costs. If we choose a smaller pipe size, it can lead to higher costs and lower pressure drops. However, if we select a larger size, it may cause erosion in the pipe.
Therefore, it’s advisable to calculate the erosional velocity before starting the line sizing process and to avoid exceeding this velocity.
Erosional velocity Formula
Ve = C/√ρ
Ve is erosional velocity in m/s.
C is A constant that depends on the characteristics of the fluid and particles (this value may vary based on empirical data or specific applications).
ρ is Density of the fluid in kg/m³.
Above is very simple formula, always use this to calculate erosion velocity.
Data Required for Pipe line sizing calculations
The data required for line sizing calculations depends on several factors, such as the application and process requirements. Below is the key data necessary for line sizing calculations, based on my experience:
- Flow Rate: The amount of flow to be used in pipe sizing.
- Allowable Pressure Drop: It’s important to know the acceptable pressure drop. This helps determine whether the line sizing is optimal.
- Fluid Density: Required for calculating erosional velocity. If using mass flow rate, fluid density is needed to convert it into volumetric flow rate.
- Darcy-Weisbach friction factor
- Pipe Length: Necessary for calculating the pressure drop.
- Pipe Schedule Number: Helps calculate the internal diameter of the pipe.
- Pipe Roughness: Important for pressure drop calculations.
- C Value: Used for erosional velocity calculations.
- Pressure and Temperature: These affect the properties of the fluid and should be considered.
- Material of Construction (MOC) of the Pipe: The MOC influences the roughness of the pipe.
Step-By-Step Procedure for Line sizing calculation
Now, I am going to explain the actual line sizing procedure for single-phase (liquid) flow. For gas or multiphase flow, we will need to follow a different procedure. While the steps are not entirely different, we must consider density changes due to the effects of compressibility.
For compressible fluids, I will write another article where I will explain everything you need to design line sizing for compressible fluids. If you want something specific, please comment here, and I will try to cover it.
Step 1 Gatherer the All Data
We alreadr learn the data which is important for calculation of line sizing. But i will tell agian that follwing least data is neccsary for line sizing calculation.
- Flow Rate in M3/s
- Density Kg/m3
- Allowable Pressure drop in Pa
- Viscosity
- Pipe length in meter
- Pipe roughness
Step 2 Calculate erosional velocity
Use the erosional velocity formula to calculate the erosional velocity, which is very important for determining the erosional velocity value. Based on this value, we can assume the velocity in the next step.
Ve = C/√ρ
Step 3 Assume velocity as per API14E
Take help from API 14E and assume a velocity to calculate the pipe diameter by using the continuity equation.
i have summarized API 14 as below. Please assume the velocity as per below table.
| Location | ft/s | M/s |
|---|---|---|
| Pump Inlet | 3 to 7 | 0.8 to 1.5 |
| Pump Discharge | 3 to 7 | 1.5 to 4 |
| Gravity Flow | 1 to 5 | 0.3 to 1.5 |
| Vapor Flow | 10 to 30 | 3.0 to 9.1 |
| Liquid Flow (General) | 3 to 12 | 0.9 to 3.7 |
| Hydraulic Flow (Water) | 3 to 7 | 0.9 to 3.8 |
| Slurry Flow | 3 to 8 | 0.9 to 2.4 |
| Gas Flow | 20 to 50 | 6.1 to 20 |
| Heat Transfer Fluids | 2 to 6 | 0.6 to 3.5 |
Step 4 Calculate pipe dimeter using equation
Use the following continuity equation to calculate the pipe diameter.
volumetric flow rate = velocity X cross sectional area
Q = V x A
where,
Q is flow in M3/s.
V is velocity in m/s.
A is cross sectional area in M2.
Step 5 Pressure Drop using Darcy-Weisbach equation
Use the Darcy-Weisbach equation to calculate the pressure drop in a pipe.
ΔP = f X L/D X v^2/2 X ρ
ΔP = pressure drop
f = Darcy-Weisbach friction factor (dimensionless)
L= length of the pipe (m)
D = diameter of the pipe (m)
ρ = density of the fluid (kg/m³)
v = flow velocity (m/s)
To calculate the pressure drop using the above equation, we need to calculate the Reynolds number first. Then, based on the Reynolds number, we need to calculate friction factor f. In a separate article, I will cover the entire procedure for this. Once you have f, substitute it into the formula and calculate the pressure drop.
Note that in this procedure, I have considered the pressure drop in a straight pipe only, without accounting for other pressure drops such as due to fittings, elevation (head), required pressure, and so on. This is just an example; in your case, you need to consider all pressure drops as well as pressure requirements
Step 6 Compare Calculated Pressure drop With Allowable Pressure drop
Compare the calculated ΔP with allowable ΔP. If it is acceptable, then your assumed velocity and calculated diameter will be fine. If not, proceed to the next step.
Based on the calculated diameter, select the pipe with the nearest diameter. In this step, check the internal diameter (ID) only, not the outer diameter (OD). Check the pipe schedule number, and select the pipe according to the ID.
Step 7 Restart calculation from Step 3
If the calculated ΔP is not within 10% of the allowable ΔP, then start again from Step 3.
Line Sizing Calculation With Example
Till now, I have discussed the required data and the steps. Now, let’s move on to the example. I have covered a single-phase liquid line sizing example.
Problem for line sizing calculation
- Application: Water transport in a chemical plant.
- Given Data:
- Pipe Roughness (ε): 0.0002 m (for typical steel pipe)
- Flow Rate (Q): 100 m³/h
- Allowable Pressure Drop (ΔP_allowable): 5 bar
- Fluid Density (ρ): 1000 kg/m³ (for water)
- Assumed Velocity (v): 2 m/s
- Pipe Length (L): 100 m
- F= 0.02
Step 1 Required data with unit
- ε: 0.0002 m
- Q: 0.0277 m³/s
- ΔP_allowable: 5 bar
- ρ: 1000 kg/m³ (for water)
- L: 100 m
Step 2 Calculate erosional velocity
Use erosion velocity formula, put C value 100 and density 1000 kg/m3.
Ve= 100/√1000
Ve= 3.1 m/s
Step 3 Assume velocity as per API14E
Use velocity 2 m.s. from API 14 E.
Step 4 Calculate pipe dimeter using equation for line sizing calculation
Put all values in the continuity equation.
D = Square root of (4 * 0.0277 / 3.14 * 2)
D = 133 MM
Step 5 Pressure Drop using Darcy-Weisbach equation
Use all given data and calculate pressure drop.
ΔP = (0.02 * 100 * 1000* 2^2) / (0.111 *2)
ΔP = 3.6 Bar
Step 6 Compare Calculated Pressure drop With Allowable Pressure drop
3.6bar<5bar, the assumed velocity and calculated diameter are acceptable.
but if we want close value of calculated ΔP, we can increase the velocity.
The required diameter is 111 mm, so based on my knowledge, we can use a 5-inch pipe. However, this depends on the schedule number. Please check the internal diameter according to the schedule number, and based on that, we can proceed with a 5-inch diameter pipe.
Standards Used for line Sizing
API 14E gives guidelines for designing and installing offshore production platforms, including recommendations for flow speeds and key factors for line sizing.
Tools and Software for Pipe sizing
As per my knowledge, the following software is used in the industry for line sizing calculations. Some industries also have their own software, but mostly, they use Excel spreadsheets for this purpose.
- Pipe Flow Expert
- AFT Fathom
- PIPESI
- HYSYS
Online Line Sizing Calculator
Put all the data in and press the calculate button. You will get the result along with tips. Use the tips for further development. If there are any errors, please comment, and I will fix them.
Update soon
Line sizing calculation excel sheet
I will update the excel soon.
Frequently Asked Questions
What standards do we use for line sizing calculations?
Answer: API 14E
What data is required for line sizing calcuation?
Answer: The data required for line sizing includes:
- Flow rate
- Allowable pressure drop
- Fluid density
- Pipe length
- Pipe schedule number
- Pipe roughness
- C value for erosional velocity calculation
- Pressure and temperature
- Material of construction (MOC) of the pipe
What are the steps for line sizing calculation?
Answer: The steps for line sizing include:
- Gather the necessary data.
- Calculate the erosional velocity using the formula
- Assume a velocity based on API 14E guidelines.
- Use the continuity equation to calculate the pipe diameter
- Calculate the pressure drop using the Darcy-Weisbach equation.
- Compare the calculated pressure drop with the allowable pressure drop.
- If the calculated pressure drop is within 10% of the allowable pressure drop, select the nearest pipe diameter based on the schedule number.
- If not, adjust the assumed velocity and repeat the necessary calculations.
Tips for Interview
Now, I will help you prepare for the interview on line sizing. First, read this article where I have covered the necessary information. My first advice is to always remember the API standards. You also need to explain all the steps and formulas, which is very important. Additionally, keep in mind the names of formulas like the continuity equation, etc. Gather information on compressible and incompressible line sizing. Always focus on the steps for liquid line sizing because it is not difficult, so you won’t get stuck.
I hope ” line sizing calculation with example” this article is okey.
Conclusion
Line sizing is very important for process engineers. We need to use API 14E for the assumption of velocity. Additionally, we must use the continuity equation and pressure drop calculations. It’s also essential to calculate pressure drop and erosional velocity. Erosional velocity is crucial to avoid erosion in piping. An optimum diameter is necessary from a cost perspective.
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