Fire Hydrant Network Analysis

Fire Hydrant Network Analysis

Fire Hydrant Network Analysis using Software J .S e el l v va ak k u um ma a r r w w k ww w . c h ho o l la a r r i i s sk . k .c o om m Introduction

The pipe distribution networks are the essential part of the fire water hydrant system. The optimal designing of the pipe network has a vital part in delivering water at required flow and pressure for fire fighting. However, there are some scenarios where outlet pressure is not sufficient for supplying the required demand. These cases may include unplanned system maintenance, fire pump failure, sudden leak or failure of any part of a large pipe distribution networks. The consequences can be severe if any fire accident happens during such failures. Hence, a robust and efficient fire water water distribution network is a must to mitigate such failures. This can be accomplished by doing a pipeline network analysis using hydraulic network modeling software like KYPIPE 2008. Also, these failure scenarios can be simulated in the software model to assess the impact and suggest solutions to mitigate the same. This article deals with the importance of using software for doing fire hydrant network analysis.

Fire Water Network

A fire water network can be defined as a set of links interconnected through nodes. In a water distribution network system, the pipes are connected to form a complex loop configuration which is created by using nodes and pipe links. Pipes are links that convey water from one point in the network to another. The node is a junction where two or more pipes combine or a point where water consumption is allocated and defined as demand. Function of these elements (links and nodes) is to lead water from the network source, which is a water reservoir, to the extremes points of the network, called hydrants.

The NFPA, OISD and TAC standards requires that the hydraulic design of the pipe distribution network meet the required flow and pressure for a hydrant or a sprinkler system. The network analysis is done during the design stages of the system and before envisaging any alteration/ modifications of the pipe network. There are many accident case histories wherein wherein the fire could not be put under control due to lack of the fire water supply because of failure of pipelines in the network. In addition, factors like pipeline corrosion and ageing of the water pipelines add to the cause of pressure loss and hence it is necessary to have robust and efficient fire water network.

The need for the fire water network analysis is to determine the water flow in each line and pressure in each node as per the standards. Cholamandalam MS MS Risk Risk Services Ltd (An ISO9001:2000 Certified Company)

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Analysis of Water Distribution Pipe Network

Pipe network problems are usually solved by numerical methods using a computer since any analytical solution requires the use of many simultaneous equations. Three simple methods used to solve pipe network problems are the Hardy Cross method, the linear theory method, and the Newton Raphson method. The Hardy Cross method that involves a series of successive approximations and corrections to flows in individual pipes is the most popular procedure of analysis.

Flow in a water pipe network, satisfies two basic principles, conservation of mass at nodes and conservation of energy around the hydraulic loops. Conservation of mass states that, for a steady state system, the flow into and out of the system must be same. This relationship hold good for the entire network and for individual nodes.

1)

Flow Continuity Equation

Consider the junction J shown in figure where five pipes are interconnected and there is an outflow demand. The directions of flows Q1, Q2and Q5 are entering the junction J, while the directions of flows Q3, Q4 and Q6 are leaving the junction J. The mass balance equation for each node can be represented as:

Q1 + Q2 + Q5 = Q3 + Q4 + Q6 this means that at any junction or node “ The sum of the inflows entering the junction equals

to

the

sum

of

the

outflows

leaving the junction ” and this is the Flow Continuity Equation :

Σ

Inflow =

Σ

outflow

2) Energy Equation The second governing equation is a form of conservation of energy that describes the relationship between the energy loss and pipe flow. Cholamandalam MS Risk Services Ltd (An ISO9001:2000 Certified Company)

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Assume that the flow direction in the pipe is from junction (a) to (b) and its value is Q, the pressure and elevation head and the mean velocity at (a) are P a , za and Va respectively, the pressure and elevation head and the mean velocity at (b) are P b, zb and Vb respectively, the total friction and fitting head losses from (a) to (b) are hL, the pump’s head is hp, all heads in are in meter. For this system:

Since the flow and pipe diameter are the same at junctions (a) and (b) thus the kinetic head at (a) equals the kinetic head at (b), the energy equation is reduced to :

In other words, “the difference in hydraulic head between any two junctions within any pipe system equals to the net head losses between the junctions”.

General procedures of the network analysis

The distributing network is either designed new or recommend an improvement or rehabilitation to the existing network system. In this case, the network systems are already designed and the system is to be analyze at different operating conditions ( i.e. at different demands ) in order to determine the capability of the networks to deliver the required pressures and flows. The general procedures of analyzing any pipe networks are: 1.

The layout of the pipe network should be determined.

2.

The characteristics of all the network components should be determined from the source to the area to be protected

3.

The two basic hydraulic equations are applied:

Flow Continuity Equation :-

Cholamandalam MS Risk Services Ltd (An ISO9001:2000 Certified Company)

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Energy Equation:-

4.

When the Flow Continuity Equation and Energy Equation are applied, a system of non-linear equations that is solved by trail-and-error manual computations or by using computer software that solve such equations.

The Need for Software for Hydraulic Analysis Network:

In a simple hydraulic system consisting of one pipe or combination of pipes in which flow directions are all known unambiguously. In more complex systems, pipes might be in combined interconnected loops in ways that makes it difficult to determine even the direction of flow in any given pipe. In such a system, where the pipe network is complex, the solution is quite complicated because it involves simultaneous consideration of continuity equation, energy conservation and head-loss function. Also, the unknown parameters are more and manual calculations becomes cumbersome, the sheer number of equations that needed to be satisfied to determine the complete flow condition is daunting. The conditions in such a system are usually solved with specialized computer program designed specifically to meet the purpose which makes the comparison of various scenarios are easy.

In addition, the software can simulate the real time scenarios (like pipe break, leakage, pump failures, corrosion effects, ageing etc) where it becomes difficult to do manually.

Over view of Software :

Pipe2008 is a powerful graphical user interface for laying out comprehensive pipe system models, accessing and running associated engineering analysis engines and presenting results in a variety of ways. The models are entirely made up of pipe links, end nodes and internal nodes. Using this approach only a few simple steps are required to develop and modify pipe systems and define the associated data.

Pipe2008 can input a background map and drawings in a variety of vector and raster formats. In addition scaled grid lines may be used. Using a scaled background map or grid lines will allow pipe links to be precisely scaled (length calculated) as they are created.


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The HydrauliCad, Pipenet, WaterCad are the other equivalent software for hydraulic network analysis. When compared to these softwares the KYPIPE has unique provision to model the hydrant system, deluge, sprinkler and water spray system in the same software. Also, more user friendly features like graphic user interface, importing/ exporting data and drawings from/to AutoCAD, excel, EPANET etc. are available. Hence the KYPIPE software is considered for illustration.

Method of Analysis

Modeling is a process of representing the piping system in a manner required for engineering calculations to be made.

The KYPIPE engine for the piping system hydraulic calculations is designed to calculate the steady state flows in all pipes and pressures for all the nodes. The KYPIPE software can be applied to any liquid and designed to accommodate any pipe configuration and a wide variety of hydraulic components such as pumps, valves (including check valves, regulating valves), any component of fittings which produces significant head loss (such as elbows, orifices etc.,) flow meters and storage tanks.

KYPIPE software is based on solving the set of mass continuity and energy equations utilizing efficient linearisation schemes to handle non linear terms. This approach accommodates elements such as closed lines, check valves and regulating valves in a direct and very efficient manner.

Pipe System Components

Data regarding the physical characteristics of the component in the pipe system are to be obtained prior to creating model for computer analysis.         

Pipe sections Pumps Check valves Regulating valves Variable pressure supply Minor loss components Storage tanks Pressure switch Flow meters

Pressure and Flow specifications

To describe the boundary pressure and flow specifications the data like flows entering or leaving the distribution system at the junction nodes (demands).

Parameter Calculation


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The KYPIPE provides a fast and accurate calculation of a variety of design, operating and calibration parameters for pipe distribution network. The parameters include:



Design parameters like: pipe diameter, pump power, pump head, storage level, and valve characteristics



Operating parameters like: pump speed, pressure regulating valve settings, control valve setting and flow or pressure specification.



Calibration parameters like: pipe roughness node demand, and minor loss coefficient

Network Elements:

Pipe distribution systems are constructed using the following two elements: (1) Pipe Links, (2) Nodes. Pipe links are uniform sections of pipes (same basic properties) following any route. A pipe link may be comprised of one or more pipe segments. A pipe segment is a straight run of pipe with no internal nodes.

Nodes are located at the ends of pipe segments and include all distribution system devices that are modeled. Internal nodes are located between two pipe segments.

End nodes are located at the

ends of all pipe links and can connect other pipe links, represent a dead end or a connection to a supply.

Internal nodes are located between two pipe segments of identical properties. The intermediate node is usually a point where a directional change occurs while the other internal nodes (valve, hydrant, in-line meter, metered connections, and check valves) are devices or model elements located in a pipe link. From the modeling viewpoint, internal nodes are essentially passive devices (they do not directly affect the calculation), although they do provide added modeling capabilities.

End nodes are located at each end of all pipe links. End nodes represent both passive connections, such as junctions and connections to supplies, and active elements, such as pumps. One or more pipe links can connect to a common end node. For non-directional end nodes (junctions, reservoirs, tanks, variable pressure supplies, and sprinklers), pipe links can be connected in any manner.

Capabilities and Unique features of the Software: Cholamandalam MS Risk Services Ltd (An ISO9001:2000 Certified Company)

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

Provides powerful graphical user interface for laying out comprehensive fire system models



Can input a back ground map and drawings in a variety of vector and raster formats



Using a scaled background map or grid lines will allow the pipelines to be precisely scaled



Can calculate the actual simulations for pump and valve conditions/ positions



Provides the necessary data for standard pipes



Simulation of age based performance is possible



Pump head and flow will develop the performance curve for the pump



Operation of required number of water outlets and developing results possible



Simulation of leaks/ pipe breaks in the network system and developing results



Options for selection of friction loss equations



Can take care of elevations, directions of flow



Can give results in terms of pressure , volume and velocity and contours



Can be used for other liquids also



Extended Period Simulation for water reservoir level possible



Selection of pumps can be made based on the system demand



Provide flexible choices for displaying results

Simulation of the Fire Hydrant Network Using KYPIPE 2008:

The pipe network comprising of the nodes and pipe links are modeled with scaled background map/ drawings. Various elements like pumps, reservoirs, hydrants, and sprinkler are included in the model as per the requirement. After representing the entire network element, the design, operation and calibration parameters (as defined in the pervious paragraph) are given as input to the model.

The model is checked for any errors and missing parameters. Model is simulated and the results are obtained for the evaluation.

The software provides the results in various forms like velocity, flow, loss for pipes and pressure, head, demand for the nodes.

Case Study:

A case study of fire water network analysis study done in a refinery may be considered as an example. The refinery has an above ground fire water pipeline network for about 65 km in length of 3

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various pipe sizes. The system has 18 main pumps of 610 m /hr and 410 m /hr capacities with 10 KSC delivery head. Nearly 1000 number of double headed hydrant are installed is in the fire water distribution system. There are four pump houses located at various locations in the refinery. The refinery had expanded its capacity over a period of 20 years and augmented the fire protection system without predicting the implications to the existing fire water network. Adding to this, due to Cholamandalam MS Risk Services Ltd (An ISO9001:2000 Certified Company)

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ageing and the nature of fire water used the pipe got corroded causing pipe rupture and major leaks at many locations.

The network analysis was done to address the problems like, 

Whether the required pressure and flow are met at the remotest hydrant/ deluge system when there are two simultaneous fire scenarios as per OISD requirement.



Impact of the pipe leak and pipe rupture



Impact of pump failures



Impact of closure of a isolation valve



Impact of ageing/ corrosion



Implications of changing the existing MS pipes to cement lined pipes

For instance, the LPG sphere storage area (see figure below) can be taken for this study. Here there are hydrants; water monitors and deluge system are provided. There are two parallel pipes running for providing fire water supply which is as the result of addition of the LPG spheres in the area.

The assessment of whether the fire protection system is meeting the OISD standards is analyzed by using KYPIPE 2008. The pipeline layout, pipe sizing (diameter & length), pipe roughness, pipe fittings, number and capacity of reservoir, number and capacity of fire pumps, number and capacity of hydrants/ sprinklers are given as input and modeled in the software.

The typical output shows the flow, velocity and direction in each pipe segment, pressures at each node (hydrants).


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Figure shows a typical fire hydrant system for a LPG sphere. [UNIT: pipe flow is given in (l/s); node pressure is given in (Kpa)]

From the analysis we can infer that delivery pressure at all hydrant outlets is not meeting the OISD requirement of 7 KSC (686 Kpa).

The fire hydrant system was redesigned by increasing the pipe size, removing the parallel pipes with all the leaks arrested. The simulation was done again.


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Figure shows the typical output with pressure contours for the LPG sphere area after pipe layout modification.

The analysis clearly shows that the all the hydrants are having the delivery pressure of greater that 686 Kpa or 7 Kg/ cm2 and required discharge.

Conclusion: From the above case study the following recommendations are suggested: 

Even though additional hydrant pipelines were laid to meet the augmented LPG storage, the existing fire water network is not meeting the required pressure and flow as per OISD standards. Hence the new pipeline layout is modeled to the get the adequate pressure.



Minimum number of pumps required to be operated for meeting this fire scenario .



The internal cement lining of the pipelines to prevent the corrosion of pipelines

The software modeling has provided a robust and efficient method of simulating a complex fire water network where the various real time scenarios can be effectively predicted. The software provides various options for input to the model and allows checking proper functioning of the system whether required pressure & flow are achieved. The results can be obtained in the form of graphs, contours, reports etc providing flexibility and through understanding of the pipe network.


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Reference:

1.

Gordan P. Mckinnon, Keith Tower, Fire Prevention Handbook , National Fire Protection Association

2.

Harry E. Hickey, Hydraulics for Fire Protection , National Fire Protection Association

3.

Cunha,

M.C.,

and

Sousa,

J.,

(1999),

“Water

Distribution

Network

Design

Optimization: Simulated Annealing Approach” , Journal of Water Resources Planning and Management, Vol. 125, No. 4, pp. 215-221. 4.

Lansey, K.E., and Mays, L.W., (1989), “Optimization Model for Water Distribution

5.

System Design”, Journal of Hydraulic Engineering, Vol. 115, No. 10, pp. 1401-1418.

6.

Dragan A. Savic, Godfrey, “A. Walters An Evolution Program For Pressure Regulation In Water Distribution Networks”, Centre for Systems and Control Engineering, UK

7.

Larry W Mays

8.

www.kypipe.com

,

“Water Distribution System Handbook”, Mc Graw Hill Handbooks.


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Fire Hydrant Network Analysis

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