auto layout technical note

8/3/2019 Auto Layout Technical Note

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PIPENET

AUTOLAYOUT

A NEW TOOLFORTHESPRAY/SPRINKLER MODULE

TECHNICAL NOTE

S U N R I S E S Y S T E M S L I M I T E D , M A Y 2 0 0 8


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May 2008 Page 2 COMMERCIAL IN CONFIDENCE


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1 S U M M A R Y

This note describes a new tool for the PIPENET Spray/Sprinkler module. The tools

purpose is to automate part of the task of designing sprinkler systems for protecting

storage/process vessels, areas or other objects/locations from the effects of fire.

2 I N T R O D U C T I O N

Defining the layout of a sprinkler system for a large vessel or area can be laborious

even with the aid of a graphical tool such as PIPENET. Automating part of this

design process will not only save time and effort, it will also allow fire-protection

rules to be encapsulated within the software and thus help to ensure that the resulting

design is compliant with fire-authority standards. This note begins with a statement

of the problem and a discussion of an illustrative example, then goes on to give a

brief description of the prototype autolayout tool. Finally, some details concerning

the variations in spray and rundown density for vessel protection are discussed.

3 S TA TE M EN T O F PR OB LE M

Given the size and shape of a plant vessel or area, design a sprinkler system to

protect it from fire. The design must either comply with applicable fire-authority

standards, such as those laid down in NFPA 15, or else satisfy a user-defined areal

flowrate and spray distribution specification.



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4 F IR E- AU TH OR IT Y S TA ND AR DS

The autolayout tool is intended to handle a variety of fire authorities' standards

and protection scenarios. By way of illustration, the application of NFPA 15 to

the design of a vessel protection system is used as an example.

4.1 Example: NFPA 15 Applied To Vessel Protect ion

The following standards from NFPA 15 are applicable to the protection of plant

vessels (reproduced from NFPA 15 Standard for Water Spray Fixed Systems for

Fire Protection, 2007 Edition)

7.4 Exposure Protection.

7.4.1* General. A system for exposure protection shall operate as intended for the anticipated

duration of the exposure fire.

7.4.2* Vessels.

7.4.2.1 Water spray shall be applied to vessel surfaces (including top and bottom surfaces of

vertical vessels) at a net rate of not less than 0.25 gpm/ft2 [10.2 (L/min)/m2] of exposed

surface.

7.4.2.2* Where rundown is contemplated, the distance between nozzles at different levels or

elevations, protecting vertical or inclined surfaces, shall not exceed 12ft (3.7m) as measured

along the surface.

7.4.2.3* The horizontal distance between nozzles shall be such that spray patterns meet or

overlap at the protected surface.

7.4.2.4 Spherical or horizontal cylindrical surfaces below the vessel equator shall not be

considered wettable from rundown.

7.4.2.5 Where projections (manhole flanges, pipe flanges, support brackets, relief valves, etc.)

will obstruct water spray coverage, including rundown on vertical surfaces, additional nozzles

shall be installed around the projections to maintain the wetting pattern that otherwise would

be seriously interrupted.

7.4.2.6 All uninsulated vessel skirts and any uninsulated steel saddles greater than

12in. (305mm) high at the lowest point shall have water spray applied on one exposed

(uninsulated) side, at a net rate of not less than 0.25 gpm/ft2 [10.2 (L/min)/m2].



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4 .2 I nte rp ret at io n

For the purposes of this application, the following assumptions are made

a) For those surfaces which are not considered wettable from rundown, the

spray pattern must be such that there is no part of the surface which receives

less than the specified minimum areal flow directly from one or more

nozzles. Since this is unlikely to be achievable without overlapping spray

patterns, the average areal flow rate on such surfaces will generally need to

be greater than the specified minimum.

b) For those surfaces which are considered wettable from rundown, the system

must be such that there is no part of the surface which receives less than the

minimum flow directly from one or more nozzles, from rundown, or from a

combination of the two. Again, practical considerations imply that theaverage flow will need to be somewhat greater than the specified minimum.

c) With rundown, the water is depleted on its way down, ie the same litre of

water cannot be considered to contribute to the minimum required areal flow

for every square metre of surface that it runs down.

4 .3 Fu lf il li ng NF PA 1 5

In the context of the above standards, the proposal for the autolayout tool is

that, based on some design information provided by the user, it will generate a

sprinkler layout which is compliant with standards 7.4.2.1 to 7.4.2.4. Standard

7.4.1 can be handled by constraining the choice of pipe material, while 7.4.2.5

and 7.4.2.6 are addressed by allowing the user to change the design manually

once the basic layout has been generated.



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5 U SE OF TH E A UT OL AY OU T T OO L

Use of the prototype autolayout tool is described in the following sections.

5. 1 Too l Selec tion

Having selected pipe types and nozzle libraries, the user selects Autolayout from the

Tools menubar item:

If an existing node is selected when the tool it launched, it will offer to join the new

sub-network which is about to be generated to that node.



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5.2 Dimensions And Spray Requirements

In the first of two dialogue windows, the user specifies the shape and size of the

object to be protected, spray density and nozzle layout requirements (which can beselected to be compliant with a built-in fire-authority standard), pipe parameters and

component labels:

In this example the diameter and height of the vessel have been entered but all other

parameters have been left at their default values.



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5.3 Nozzle Conf igurat ion

In the second dialogue the user can adjust the nozzle configuration (within the

constraints imposed by the selected standard). Based on the information suppliedtogether with the parameters of each nozzle in the library, values such as pressure,

total flowrate and overlap are displayed for each nozzle type.

Having adjusted the nozzle configuration values interactively and selected the nozzle

type from the list, the user then clicks on the Finish button.



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5.4 The Generated Layout

The generated sub-network is drawn on the schematic grid ready for further editing.

Fittings are included on the pipes, and pipe-sizing can be performed in the usual way.

Note that the generation of this example involved seven mouse-clicks and the entry

of two numbers: a further two mouse-clicks were involved in having it joined to theexisting node automatically.



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5.5 Area Protect ion Example

The following screen-shots show the two dialogues and generated sub-network for an

area protection scenario:



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6 S PR AY D EN SI T Y C ON SI DE RA TI O NS

For surfaces which are not considered wettable from rundown, the choice of nozzle

configuration depends on whether the flowrate requirement is an average or a

minimum

average flow requirement: the total required flow defines the number of

nozzles, which are then distributed in a near-uniform arrangement such

that, overall, the surface receives the correct areal flow;

minimum flow requirement: the nozzles are distributed in a covering

arrangement, such that no part of the surface receives less than the minimum

areal flow directly from one or more nozzles.

The autolayout tool will allow for either option. Note that meeting the second of

these requirements is complicated by the fact that, even with uniform spray densitywithin the spray cone, the areal flow striking the vessel surface will vary with

angular distance from the centre of the cone. This is because, with increasing angular

distance from the centre of a nozzles spray pattern

the distance to the vessel surface increases, reducing the spray density in the

diverging cone;

the angle of incidence on the vessel surface increases, spreading the flow

over a larger area of vessel.

For surfaces which are considered wettable from rundown, there is an additional

factor causing the rundown density to vary the height over which rundown is

accumulated decreases with increasing horizontal distance from the centre of a

nozzle's spray pattern. The variation in rundown density is illustrated below



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Again, the choice of nozzle configuration depends on whether the flowrate

requirement is an average or a minimum.



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6.1 Calculation Of Rundown

The autolayout tool will calculate rundown as outlined in the following diagram,

which shows (in elevation view) the spray patterns from nozzles N1 and N2overlapping on the side of the vessel:

In the column from the top of the area protected by these nozzles to the point P, the

areal flowrate including rundown is given by

RP=1

hP

y=yP

y=yPhS

F1 xP , y F2 xP , y . dy

where Fn(x,y) is the areal flowrate at (x,y) from nozzle n.

By handling the variation of spray and rundown density rigorously, the autolayout

tool will allow the user to ensure that the minimum flowrate requirement is truly met

at all points around a vessel where this is a design requirement, and to do so in the

most economical way (minimizing total flowrate in order to keep supply piping and

pumping costs to a minimum, for example).



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7 C ON C L UD I NG RE M AR KS

The autolayout tool is not intended to produce a finished, certified design or

to provide a substitute for the user's expertise and engineering judgement it

is primarily a productivity aid.

The autolayout tool will be extended to handle a variety of vessel shapes and

other fire protection scenarios.

The autolayout tool will be extended to support a variety of fire protection

standards, with the user choosing which standard is applicable or else

specifying the spray density and other requirements directly.

The purpose of this note is to gauge opinion on the way in which the

autolayout tool is presented to the user, and to invite further comments and

suggestions. The information contained in this note is strictly confidential and is not to be

shared with third parties without the express agreement, in writing, of

Sunrise Systems Ltd.


auto layout technical note

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