Pipe Size Calculation for Steam Supply

Abstract

Pipe designers and engineers often encounter complex mathematical equations to determine the diameter required for adequate steam discharge capacity at specific flow velocities. This article aims to simplify the calculation of steam pipe sizes. The formulas and factors derived herein can be utilized for determining pipe diameters in steam applications. Ultimately, the findings provide engineers and designers with practical tools to enhance the reliability and efficiency of steam system.

Introduction

I. INTRODUCTION

The effective design and sizing of steam pipes are critical for optimizing system performance and ensuring operational safety in industrial applications. This article presents a comprehensive methodology for calculating steam pipe sizes, considering factors such as steam pressure, flow rate, temperature, and the physical properties of steam. Our handy formula significantly streamlines the steam pipe sizing process, enabling designers to achieve accurate results in a fraction of the time required by conventional methods. Traditional calculations often involve complex equations and lengthy analyses, requiring frequent reference to steam tables and other resources, which can be cumbersome and time-consuming. By simplifying these calculations, our formula reduces the workload for engineers while maintaining accuracy,

II. STEAM PIPE SIZE CALCULATION

The continuity equation, expressed as Q=AV, is fundamental in fluid dynamics, illustrating the relationship between volumetric flow rate, cross-sectional area, and flow velocity. In this equation, Q represents the volumetric flow rate, A is the cross-sectional area of the pipe or channel, and V is the velocity of the fluid. Understanding this equation is crucial for engineers and designers when sizing pipes and ensuring efficient fluid transport in various applications.

A.. Key Parameters for Steam Pipe Sizing

• Steam Flow Rate: The mass flow rate of steam, typically given in tons per hour (TPH) or kilograms per second (kg/s).
• Steam Pressure: Usually provided in bar (either gauge or absolute pressure).
• Specific Volume: The volume occupied by one kilogram of steam, which depends on the pressure and temperature of the steam. This is obtained from standard steam tables.
• Steam Velocity: The desired velocity of the steam through the pipe, generally recommended to be between 25 to 35 m/s for process steam systems to balance efficiency and safety.

B. Derivation of formula for Steam Pipe Size Calculation

Q= AV

A= π4D2

Q= π4D2V

                                                                                            D=4QπV      .  .  .  .  .  .  .  .  .  .  .  .  .(i)

       Where:

D             : Pipe diameter

V             : Average velocity in the pipe

Q             : Volumetric flow rate of Steam

Generally, in the industry, the flow of steam is referred to and measured in TPH (tons per hour). Therefore, we first need to convert the flow of steam from TPH to m³/hr, transforming it into volumetric flow. For this conversion, we refer to the steam table to find the specific volume of steam at the selected pressure and temperature. In industrial applications, process steam is typically used at saturated temperatures or with a few degrees of superheat.

                                                                                                 
                                                Q= TPH10003600v 109       .  .  .  .  .  .  .  .  .  .  .  .  . (ii)
 
         Where:

Q             : Volumetric flow rate of Steam (mm3/sec?)          

TPH        : Steam flow rate (tons per hour)

v               : Specific volume of steam at particular pressure and temperature (m3/kg )

Note: When selecting the specific volume of steam from the steam table, it is important to consider that the pressure measured in the industry is "gauge pressure," while the pressure listed in the steam table is "absolute pressure." Ensure to convert gauge pressure to absolute pressure for accurate calculations. A small steam table is provided in this article (Table 2) for the reference.

By substituting the value of Q from equation (ii) into equation (i)

                                                     D=4*TPH*1000*v*109π*V*3600*1000     .  .  .  .  .  .  .  .  .  .  .  (iii)
   Where:

D             : Pipe diameter (mm)

V             : Average velocity of steam in the pipe (m/sec)

The equation (iii) is the comprehensive formula which can be directly used to calculate the pipe diameter for steam pipeline. The value of following 3 variables.

1. TPH – The process steam flow / steam consumption in the industrial application in ton per hour.
2. v   -  Specific volume of steam at particular pressure and temperature (m3/kg ) from steam table.
3. V - The average velocity of steam in the pipe (m/sec) is generally considered to be between 25 and 35 m/sec for process steam applications.

C. Simplification of Calculation and Generation of Handy Formula

                                              D=4*TPH*1000*v*109π*V*3600*1000     .  .  .  .  .  .  .  .  .  .  .  (iii)

                D= TPH ×4*v*109π*V*3600      .  .  .  .  .  .  .  .  .  .  .  (iv)

In the equation (iv), If the velocity is fixed then the value of 4*v*109π*V*3600   will be a constant “C2”.

Where, C2 is the constant value at a fixed velocity of steam in pipeline. Let’s call it DC factor for “Steam pipe size calculation”.

The above formula provides a straightforward method for calculating pipe sizes based on a given flow rate of steam and its velocity of flow.

D. DC factor for Steam Pipe Size Calculation

The values of DC factor at different velocity are given in Table 1 for Steam pipe size calculation.

TABLE 1
DC factor at different velocity of Steam in pipe

E. How to use “Handy Formula”:

1. To calculate the pipe diameter in millimeters, multiply the square root of the flow QQQ value in TPH (tons per hour) by the DC factor at the selected velocity from Table 1.
2. Please note that the calculated pipe size refers to the inner diameter of the pipe.

EXAMPLES - 1

Calculate the required pipe size for a steam flow rate of 50 TPH (tons per hour) at saturated temperature and 8 bar pressure, with a velocity of 25 m/s, using the formula Q = AV.

SOLUTION          

Flow (TPH)           -               50 TPH

Velocity V             -               25 mps

Pressure -               8.0 bar (G)

Let's find the specific volume of steam at 8 bar gauge pressure, which is approximately 9 bar absolute pressure, from the steam table (Table 2).

Specific volume (v)             -               0.215 m3/kg

Put the above values in the equation (iii)

D=4*TPH*1000*v*109π*V*3600*1000

D=4*50*1000*0.215*109π*25*3600*1000

D=7*4*50*0.215*10622*25*3.6

D= 103* 3011980

D= 103* 0.3898977

D= 389.89 mm (inner diameter of pipe)

The next available pipe size in the market is 400 NB, Hence selected pipe size shall be 400 NB for the given parameter in the question.

EXAMPLES - 2

Calculate the required pipe size for the steam having parameter same as mentioned in the example – 1 by using “DC Factor” method / Handy formula.

SOLUTION          

Flow (TPH)       -               50 TPH

Velocity V        -               25 mps

Pressure             -               8.0 bar (G)

DC Factor for steam at 8 barG pressure and 25 m/sec velocity (C2) – 55.14

D= TPH× C2  . . . . . . . . . .  .(ii)

D= 50× 55.14  

D= 389.89 mm (inner diameter of pipe)  

Here, we can see that the calculation of Steam pipe size is  very simple by using the DC factor.

EXAMPLES - 3

What will be the pipe size for the steam flow rate of 17 TPH at 6 barG pressure and at a velocity of 30 mps?

SOLUTION          

Flow (TPH)           -               170 TPH

Velocity V             -               30 mps

Pressure -               6.0 bar (G)

DC Factor for steam at 6 barG pressure and 25 m/sec velocity (C2) – 56.72

D= TPH× C2  . . . . . . . . . .  .(ii)

D= 17× 56.72  

     D= 233.86 mm (inner diameter of pipe)

The next available pipe size in the market is 250 NB, Hence selected pipe size shall be 250 NB for the given parameter in the question.

III. STEAM TABLE

TABLE 2

IV. CONSIDERATIONS AND LIMITATIONS

When calculating the pipe size for steam systems, it is important to take into account the following precautions to ensure an optimal design

A. Avoid Excessive Steam Velocities

High steam velocities can cause erosion of the pipe's inner walls, leading to wear and tear over time. It can also result in noise and vibration in the system, leading to mechanical stress. Ensure that the selected velocity (typically 20 to 40 m/s) does not exceed the recommended limits for the system.

B. Account for Pressure Drop

In long pipelines, pressure drop due to friction can become significant. Smaller pipe diameters result in higher pressure drops. Always calculate the expected pressure drop across the length of the pipeline to ensure that the pressure at the end point is adequate for the application.

C. Allow for Pipe Expansion

Steam pipes expand due to heat, especially when dealing with high-pressure steam. Consider using expansion joints or flexible connectors to accommodate the thermal expansion and prevent damage to the system.

D. Standard Pipe Sizes

Ensure that the calculated pipe diameter corresponds to commercially available standard sizes. Piping standards such as ASME B31.1 or API standards should be consulted to select the appropriate pipe size.

E. Safety Margins

It’s a good practice to select a slightly larger pipe size than the calculated value to accommodate future expansion of the system or unforeseen variations in steam flow demand. This helps prevent overloading the system in the long run.

F. Consider Steam Traps and Condensate Return

In systems where saturated steam is used, condensation will occur, and steam traps will be required to remove the condensate. The pipe sizing should consider the installation of steam traps and ensure that condensate does not collect in the pipe, which could lead to water hammer.

G. Ensure Proper Insulation

Steam pipes must be properly insulated to prevent heat loss and maintain the efficiency of the system. The insulation also reduces the risk of accidental burns and minimizes thermal stress on the piping system.

Conclusion

The DC factor is a multiplying factor at a particular velocity of Steam to calculate the pipe diameter by multiplying it with the square root of mass flow (TPH). By using the DC factor, the calculation becomes very easy to calculate the Steam pipe size.

References

[1] RS Khurmi – Steam table - Key thermodynamic data for saturated and superheated steam [2] Dr. R.K. Bansal, Fluid mechanics and hydraulic machines, ninth edition 2010 [3] ASME B31.1: Code for Power Piping. [4] API Standards: Guidelines for the design and selection of steam systems. [5] Your Paper ID is : IJRASET64645

Copyright

Copyright © 2024 Dinesh Chauhan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.