© Commonwealth of Australia 2 - npstag.comnpstag.com/wp-content/uploads/2016/05/CPCPGS3051A... · Purge or purging ... Preparing to purge using nitrogen ... • job safety analysis

© Commonwealth of Australia 2

CPCPGS3051A - PURGE CONSUMER PIPING

ii © Commonwealth of Australia 2015

CONSTRUCTION, PLUMBING AND SERVICE

INTEGRATED FRAMEWORK

TRAINING PACKAGE

CPC08

CPCPGS3051A

PURGE CONSUMER PIPING

LEARNING GUIDE


© Commonwealth of Australia 2015 iii

ACKNOWLEDGEMENTS

National Plumbing Services Training Advisory Group

Plumbing Industry Commission Victoria

© Commonwealth of Australia 2015

Construction and Property Services Industry Skills Council PO Box 151 Belconnen ACT 2616 Tel: 02 6253 0002 www.cpsisc.com.au This work is copyright, but permission is given to trainers and teachers to make copies and contextualise the resources for use within their own training organisation or in a workplace where training is being conducted. This permission does not extend to making copies for use outside the immediate training environment for which they are made, or the making of copies for hire or resale to third parties.

This work was first published in 2004 with the assistance of funding provided by the Commonwealth Government through the Australian National Training Authority (ANTA). The 2015 publication has been updated to reflect changes to the national units of competency.

The views expressed in this work do not necessarily represent the views of the Commonwealth of Australia or CPSISC. In addition, the Commonwealth of Australia and CPSISC do not give warranty or accept any legal liability in relation to the content of this work.

The website addresses and other contact information provided in this publication were compiled in good faith and were correct at the time of printing. The updating of these resources was completed by:

National Plumbing and Services Training Advisory Group, with funding and support provided by the Construction and Property Services Industry Skills Council (CPSISC):

This guide was developed in consultation with representatives of the Plumbing Industry by NPSTAG and CPSISC to support the implementation of the CPC08 Construction, Plumbing and Services Training Package.


iv © Commonwealth of Australia 2015

Contents

What is this resource about? ................................................................................................ 1

How do I use this resource? ................................................................................................. 1

Flexible Delivery ................................................................................................................. 1

What do I have to do? .......................................................................................................... 2

Purge consumer piping ........................................................................................................ 2

Unit Descriptor .................................................................................................................... 2

Element ................................................................................................................................ 2

Performance Criteria ........................................................................................................... 2

How will I be assessed? ....................................................................................................... 4

Are there any pre-requisites? ............................................................................................... 4

What other resources will I need? ....................................................................................... 5

Texts .................................................................................................................................... 5

Web sites ............................................................................................................................. 5

Video or audio cassettes ...................................................................................................... 5

Safety ................................................................................................................................... 5

Workplace environment and safety ..................................................................................... 5

Introduction ......................................................................................................................... 5

Purge or purging .................................................................................................................. 6

Environmental concerns ...................................................................................................... 9

Gases used for purging ........................................................................................................ 9

Replacing fuel gas with inert gas or air ............................................................................... 9

Replacing inert gas or air with fuel gas ............................................................................... 9

Before purging ................................................................................................................... 10

Preparing to purge large volume gas installations ............................................................. 10

Quality assurance ............................................................................................................... 11

Work notices ...................................................................................................................... 11

Pre-installation ................................................................................................................... 11

Preparing to purge using natural gas ................................................................................. 11

Preparing to purge using nitrogen ..................................................................................... 12

Safety, tools and equipment............................................................................................... 12

Purging a service pipe ....................................................................................................... 14

Purging a sub-meter ........................................................................................................... 14

Determine purge requirements .......................................................................................... 15

Selecting the purge medium .............................................................................................. 15

Precautions ........................................................................................................................ 15

Purging a small volume gas installation ............................................................................ 16



© Commonwealth of Australia 2015 v

Purging through an appliance fitted with an open burner ................................................. 16

Purging through an appliance fitted with a flame safeguard device ................................. 17

Electronic flame safeguard device fitted ........................................................................... 17

Thermo-electric or bi-metallic device fitted ...................................................................... 17

Electrical safety bonding or bridging ................................................................................ 18

Purging a large volume gas installation ............................................................................ 19

Using the equipment to purge ........................................................................................... 21

Purging the meter .............................................................................................................. 21

Purging the installation ..................................................................................................... 22

Gas sample test methods ................................................................................................... 23

Detergent in water method ................................................................................................ 23

Gas detector method .......................................................................................................... 23

Purging consumer piping of fuel gas ................................................................................. 24


Replacing air or natural gas using nitrogen ....................................................................... 25

Introduction ....................................................................................................................... 25

Volume of nitrogen required ............................................................................................. 25

Purging with nitrogen ........................................................................................................ 27

Nitrogen set pressures ....................................................................................................... 29

Preparation for purge commences ..................................................................................... 30

Carry out and test purge operation .................................................................................... 31

Testing for completion of purge ........................................................................................ 31

Clean up ............................................................................................................................ 33

Worksheet ......................................................................................................................... 34

Practical application .......................................................................................................... 40

Assessment checklist ......................................................................................................... 42

Worksheet ......................................................................................................................... 42


© Commonwealth of Australia 2015 1

What is this resource about?

CPCPGS3051A – Purge consumer piping. This resource will help you gain the skills and knowledge

necessary to demonstrate competence in this unit.

How do I use this resource?

This resource is divided into four main sections:

• A learning unit, which contains background information on CPCPGS3051A – Purge consumer

piping

• Worksheets, which prepare you for the practical application

• Practical application, which allows you to experience purge consumer piping

• Assessment materials, which help you demonstrate competency

To complete this unit of competence you will need to:

• read the information contained in the learning unit

• complete the worksheets as instructed

• have your answers checked by your trainer or supervisor

• work with your trainer or supervisor to practise purging consumer piping

• read the assessment checklist together with the assessment sheets

• complete the assessment.

Learning Resources are not intended to be the only source of information nor are they intended to be

an exhaustive form of instruction.

Flexible Delivery

The Trainer or Supervisor may adapt and deliver this Learning Resource to suit people from diverse

backgrounds to meet equity principles and conform to Legislative policies.



What do I have to do?

To demonstrate competence in this unit you will be required to show the level of skills and knowledge

for each of the elements involved in CPCPGS3051A – Purge consumer piping. The elements are:

• prepare for purge

• determine purge requirements

• carry out and test purge operation

• clean up.

If you are unsure of the meaning of these elements you should read the performance criteria on the

following page.

CPCPGS3051A Purge consumer piping Unit Descriptor This unit of competency specifies the outcomes required to

purge consumer gas piping systems.

Element Performance Criteria Elements describe the

essential outcomes of a

unit of competency.

Performance criteria describe the performance needed to

demonstrate achievement of the element. Where bold

italicised text is used, further information is detailed in the

required skills and knowledge section and the range

statement. Assessment of performance is to be consistent

with the evidence guide.

1 Prepare for purging 1.1 Design drawing and specification are obtained

1.2 Work health and safety (WHS) and environmental requirements associated with purging consumer gas piping

systems are adhered to throughout the work

1.3 Quality assurance requirements for company operations

are identified and adhered to

1.4 Work is planned in conjunction with others involved in or

affected by the work

1.5 Appropriate tools and equipment for the conduct of

purging, including personal protective equipment, are

identified, selected and checked for serviceability

1.6 Work area and materials are prepared to support efficient

purging of consumer gas piping system

2 Identify purge

requirements

2.1 Installation is checked to ensure compliance with standards

and relevant specifications

2.2 Volume of piping system is determined from design

drawing and standards, and calculations are recorded in

format required by job specification

2.3 Method of purging is selected in compliance with standards

and authorities' requirements

2.4 Purge medium is selected in compliance with standards, and



calculations of the purge medium volume are recorded in

format required by job specification

3 Carry out and test purge

operation

3.1 Outlet point for purge gas is located and purge site is

checked for ignition sources

3.2 Purge is carried out according to standards or statutory and

regulatory authorities’ requirements and sustainability

principles and concepts

3.3 Completion of purge is verified by test equipment, or by

recognised and approved workplace testing procedures

4 Clean up 4.1 Work area is cleared and materials disposed of, reused or

recycled according to legislation, regulations, codes of

practice, and job specification

4.2 Tools and equipment are cleaned, checked, maintained and

stored according to manufacturer recommendations and

workplace procedures

4.3 Information is accessed and documentation completed

according to installation requirements

Required knowledge Required knowledge for this unit is:

• characteristics of materials used in the purging process

• effect of heat on the materials used during the purging

and testing process

• electrical safety and requisite precautions

• how to access relevant information, including codes and

technical standards

• job safety analysis (JSA) and safe work method

statements (SWMS)

• procedures for purging gas piping systems, including

isolation processes and procedures

• properties of gas, gas safety, combustion principles,

ignition principles, pressure and flow rates

• relevant statutory requirements related to purging gas

piping systems

• SI system of measurements

• workplace and equipment safety requirements

An up to date version of the ‘Unit Descriptor’ may be located on the Australian Government web site

training.gov.au

http://training.gov.au/Search/Training?searchTitleOrCode=&nrtSearchSubmit=Search&includeSupers

ededData=true&includeSupersededData=false&homePage=true&javaScriptEnabled=true&typeAllTra

iningComponents=true



How will I be assessed?

Your trainer or supervisor will decide with you how you will be assessed. Your assessment activity

may include completion of the student worksheet and practical task selected by your trainer or

supervisor. Your assessment should allow you to demonstrate all the skills and knowledge required to

purge consumer piping.

This unit may be assessed in conjunction with other units of competence. Your trainer or supervisor

will tell you if you are to be assessed this way.

Are there any pre-requisites?

Prior to commencing CPCPGS3051A – Purge consumer piping you must have successfully completed

the following pre-requisite:

• CPCPCM2043A Carry out WHS requirements

It is also recommended that prior to commencing CPCPGS3051A – Purge consumer piping you

should have successfully completed the following competencies:

• CPCPGS3056A – Install gas piping systems

• CPCPGS3058A – Install and commission ‘Type A’ gas appliance.

Project work may also group pre-requisite and or co-requisite competencies together to carry out such

projects. It is recommended that the following competencies are grouped with this unit of competency:

• CPCPGS3056A – Install gas piping systems

• CPCPGS3058A – Install and commission ‘Type A’ gas appliance.



What other resources will I need?

To assist you the following resources have been suggested and should be available to you to do this

competency:

Texts

• AS/NZS5601 - Gas Installations Relevant Version.

• State or Territory regulations may override this Learning Guide.

Web sites

Video or audio cassettes

Safety

Workplace health and safety (WHS) requirements need to be observed in accordance with legislation.

You need to know the WHS laws governing your job. Revision of CPCPCM2043A - Carry out WHS

requirements, before commencing this unit is advisable

In any work situation you can reduce the risk of injury to yourself and others by using appropriate

personal protective equipment (PPE). The types of PPE that you will need include:

• overalls – used for the protection of the installer when working in different conditions

• boots – it is recommended that soft soled footwear is worn while working on roofs, as deep

grooved footwear pick up small stones and debris that might damage or scratch the roof sheets

• safety glasses or goggles to protect the eyes from injury when cutting the sheets with a power

saw

• ear plugs or muffs to protect the installer’s hearing from excessive noise

• dust masks or respirators to protect the user from breathing in dust or fine particles when

cutting the sheets with a power saw

• gloves, for the protection of the installer’s hands when working with different types of pipes,

tools and equipment.

Workplace environment and safety

Handling of materials Manual lifting and handling techniques must always be followed

according to WHS requirements. You should move materials into

position by hand where possible. Excessive manual handling should be

avoided and cranes and other mechanical lifting devices should be

employed when necessary.

Introduction

In this unit you will look at how to purge consumer piping utilising a variety of purging mediums and

methods. Purging is defined in (relevant version) AS/NZS5601 - Gas Installations as follows.



Purge or purging

With respect to consumer piping means:

• replacing the air in consumer piping with gas or inert gas

• removing the gas from consumer piping by replacing the gas with either air or an inert gas.

Note

The purpose of purging is to prevent the presence in the piping

of an explosive mixture of fuel gas and air.

It is important that all purging operations are performed safely and that the relevant requirements of

(relevant version) AS/NZS5601 - Gas Installations are met.

Only persons with adequate training and experience should carry out purging operations.

Layout of pipework from main to meter

Purging is necessary to prevent the occurrence of an air or gas mixture that might cause an explosion

in consumer piping, in an appliance, or in a confined space.



Purging needs to be carried out in the following areas:

• a service pipe (normally the function of the authority)

• a sub-meter

• a small volume installation with gas (volume up to 0.03 m3)

− through an appliance fitted with an open burner

− through an appliance fitted with a flame safeguard device

• a large volume gas installation (volume exceeding 0.03 m3)

• consumer piping of fuel gas.

Purging must be undertaken before commencing work and after completion of work. This is to avoid

the possibility of an explosive air or gas mixture existing or forming in consumer piping, appliances or

confined spaces.

Fuel requires oxygen to burn, without oxygen it is impossible for any fuel to burn. This would mean

that if a sealed container were completely full with a fuel gas then it would be impossible to ignite the

gas even from inside the container.

We have three sealed containers which have been filled with air, fuel gas and a mixture of fuel gas and

air. Each container has an ignition source placed at the side. The ignition source is a push button piezo

igniter. What will happen if the buttons of the piezo igniters are pushed?

Examples of the three conditions

Nothing will happen in number one, because there is only air and no fuel. Nothing will happen in

number two, because there is only fuel and no air. But in three if the ratio is correct then there will be

an explosion.

Note

The flammability limits for natural gas are 5% to 14% and for

propane 2.5% to 9.5%



Consider a 100 mm copper pipeline, which is filled with air, the contents of the line would be regarded

as safe. If this same 100 mm copper pipe were filled completely with fuel gas, it would also be

considered safe. If the pipe had a mixture of fuel gas and air then this could be considered a dangerous

situation.

Purging the pipeline so it is either full of air or fuel gas or inert gas will prevent this potentially

dangerous situation.

Note

An inert gas means: a non-explosive gas, such as nitrogen.

Note

As defined in (relevant version) AS/NZS5601 - Gas

Installations, Purging is carried out to avoid the possibility of an

explosive air or gas mixture existing or forming in consumer

piping, appliances or confined spaces.

Requirements for when purging must take place are in (relevant version) AS/NZS5601 - Gas

Installations.

Definition:

• small volume gas installations = volume up to 0.03 m3

• large volume gas installations = volume more than 0.03 m3.

All consumer piping wherever possible, should be purged to a well ventilated area. Because of the

lower capacity of small volume gas installations, the amount of gas dispersed during purging is not

regarded as a problem.

For example, small volume gas installations may be purged at a cooking appliance inside the building.

Small volume gas installations are the type found in most domestic houses.

Large volume gas installations should be purged to the outside atmosphere. The purge outlet should be

at least 6 m away from any ignition source and well clear of any opening to the building.

Two methods used to purge large volume gas installations are:

• purge stack

• purge bucket.

Other purging methods may be acceptable. Persons likely to carry out purging on a regular basis may

consider obtaining IGE/UP/1A, Soundness testing and direct purging of small low pressure Industrial

and commercial natural gas installations. The document was published in 1998 by the Institution of

Gas Engineers (UK).



Environmental concerns

Because of concerns regarding the environmental impact of methane in the atmosphere, the volume of

vented gas should be kept to a minimum.

Gases used for purging

There are a number of gas mediums that can be used to purge consumer piping, and submetres:

• nitrogen

• carbon dioxide

• air

• fuel gas.

For the purpose of purging, these gases have different characteristics and different uses.

Replacing fuel gas with inert gas or air

The gases nitrogen, carbon dioxide and air are used to replace fuel gas in a pipeline. This would be

done where consumer piping is to be opened for alteration, repair or extension. The section involved

should be turned off from the supply at a convenient point and the piping vented to the atmosphere.

Nitrogen and carbon dioxide are both inert gases, with nitrogen being the preferred inert gas and

carbon dioxide being an acceptable alternative.

Replacing inert gas or air with fuel gas

After the installation of a new gas pipeline or after the alteration of an existing line it is necessary to

fill the line with fuel gas. This would mean removing air or an inert gas from the line and replacing it

with a fuel gas. The fuel gas could be natural gas, liquefied petroleum gas or other gas depending on

the gas being supplied.

Showing flow of gases through new and existing installations

Worksheet

Now go to the Worksheet and answer Questions 1 – 6.



Plan work activities

When you are purging consumer piping, you must remember your company’s WHS and quality

assurance responsibilities and those that may apply in the workplace because of the nature of the work.

It is important to ensure that all purging operations are performed safely and that the relevant

requirements of (relevant version) AS/NZS5601 - Gas Installations are met.

Before purging

The following precautions are to be taken before purging commences:

• do not commence any purging operation until a purge area has been defined, made safe and

cleared of all ignition sources, eg. naked flames, pilot lights, electrical switchgear, etc

• do not allow smoking in or near the purge area

• purging must be planned to occur when it does not affect or interfere with others on the site

• a suitable outlet point for the purge gas should be located

• a purging area should be defined before the purging operation can commence. The area must

be made safe and cleared of all sources of ignition, eg naked flames, pilot lights, electrical

switchgear.

On small volume gas installations when purging air from the line to replace with fuel gas:

• safety glasses must be worn at all times when purging and when lighting appliances

• plan a system of purging which will ensure that no pockets of air will be left within any part of

the pipework

• ensure that all appliance connections are gas tight, all appliance gas cocks are turned off and

there are no open ends in the pipework

• purge only into a well ventilated area which is free from any possible ignition sources,

mechanical air inlets and other potential hazards.

Special care should be taken when using heavier than air gases such as LP gas, to make sure the gas

has completely dispersed before applying an ignition source.

Preparing to purge large volume gas installations

A minimum of two qualified persons should be on site during the purge, one at the meter or inlet valve

and one monitoring the purge stack. A further person may be required to act as a messenger.

The first part of the purging operation is common both to purging the system of air with natural gas

and also purging the system with inert gas followed by natural gas.



The purging operation is to be carried out in the following sequence:

• main run, (meter to the furthest point)

• the branch nearest the meter, followed by all other branches (moving away from the meter

towards the end of the fitting line).

Quality assurance

Most companies these days have a policy for assuring quality to the customer. This policy is designed

to control the processes used within the company, record keeping, quality of materials used and the

way the work is done. You need to be aware of your company’s particular quality assurance

requirements. These could include:

• workplace operations and procedures

• quality of material

• control of handling procedures

• use and maintenance of equipment

• attention to specifications.

Work notices

Before attempting a purge, notices and other paperwork may be required by the relevant authorities.

Depending on laws in your State or Territory, it may be necessary before beginning any work, for you

to obtain work notices and submit them to the relevant authorities. Consult your local authority to find

out what is required in your area.

Pre-installation

An inspection must be made of the existing installation, with the aid of a design drawing obtained

from job supervisor, to ensure that it meets the regulations and specifications.

Preparing to purge using natural gas

Ensure that all testing is completed and that all open ends are sealed.

Ensure that any purging equipment has been correctly assembled and is located in a safe place free of

ignition sources.

Check that all valves are closed including:

• meter inlet

• branch valves

• appliance isolating valves

• purge hose inlet and purge stack (if used).



Preparing to purge using nitrogen

Ensure that the purging and inert gas equipment is correctly installed.

Ensure all valves are closed on:

• the cylinder and its hose

• the meter inlet

• all appliance isolating valves

• the inlet to the purge hose

• the purge stack.

Note

All aspects of the installation must comply with (relevant

version) AS/NZS5601 - Gas Installations.

Safety, tools and equipment

The tools, equipment, and personal protective equipment (PPE) must be appropriate for the

installation. Tools and equipment must be safe to use and used correctly.

Tools used for purging must be kept in good condition so that they may be relied upon.

When you purge consumer piping, the tools and equipment you need could include:

• ladders

• hand and power tools

• testing equipment

• limited height scaffolding

• elevating work platforms



• warning signs

• gas detector

• witches hats for cordoning off the purge area

• fire extinguishers.

All your equipment should be in good working order so as not to place you at risk. Ladders should be

checked to make sure they are not damaged and in safe working order. If scaffolding or elevated work

platform needs to be erected then this must be done in accordance with your local State or Territory

regulations.

While carrying out the purging process you should guard against the chance of explosion. One of the

most important issues in regard to safety is the possibility of an explosion due to the ignition of fuel

gas. This is why you should purge only into a well ventilated area which is free from any possible

ignition sources, mechanical air inlets and other potential hazards. Do not smoke in or near the purge

area. Warning signs may be used to assist you in stopping the possibility of accidental ignition.

Warning signs

The personal protective equipment you will need may include:

• overalls

• boots

• safety glasses or goggles

• hard hats


Overalls provide an outer layer of protection to the body. Overalls should be worn during all stages of

the purging process. Boots provide protection to the wearer’s feet and should be worn during all stages

of purging. Safety glasses or goggles must be worn to protect the eyes from damage while purging,

due to the possibility of an explosion. A hard hat is to be worn to provide protection to your head and

should be worn at all times. When this equipment is not being used it should be cleaned and stored in a

safe place.



Worksheet


Purging a service pipe

Purging a service pipe, (ie. the portion of piping between the gas main and the consumer billing

meter), is normally the function of the authority.

Note

If others are permitted to purge a service pipe, the purge is to be

carried out in accordance with the authority’s procedure. This is

stated in (relevant version) AS/NZS5601 - Gas Installations.

Purging a sub-meter

The (relevant version) AS/NZS5601 - Gas Installations (1.4.77.2) defines a sub-meter as a ‘meter for

measuring gas which has already passed through a consumer billing meter’.

An example of where we may find a sub-meter would be on a block of flats or apartments. The block

may have a meter that measures the amount of gas used by the building and sub-meters at individual

flats to measure the amount of gas being used by each occupant. Sub-meters may also be used in a

factory to find out the amount being used by an appliance. In general terms sub-meters are installed

after the main billing meter so that a section or sections can be divided off to obtain information as to

the use of that section.

Main billing meter with sub meters



Determine purge requirements

Before you can begin the purge, you need to know about the system. There are several things you need

to check on. These are:

• check volume of sub-meter. Where a sub meter is to be purged, the volume of the meter is

indicated on its badge

• on any approved gas meter there must be an identification badge, which provides information

on the volume of the meter

• determine volume of purging medium. Where a sub meter is to be purged, a volume of

purging medium equal to five times the volume held by the meter is required to achieve an

acceptable purge. Observe the test dial or index to ensure the correct amount has passed

through the meter.

Note

The volume of purging medium must be in accordance with

(relevant version) AS/NZS5601 - Gas Installations.

Selecting the purge medium

The purge medium must be appropriate for safe purging of a sub-meter.

The purge medium to use for a particular job will depend on which type of purge you want to do. Is

the purpose of the purging to remove the fuel gas, as when preparing to work on an existing line, or is

it to remove the air from the line, as in the case of a newly installed gas fitting line?

Note

The purging medium selected must be in accordance with

(relevant version) AS/NZS5601 - Gas Installations.

Precautions

• Do not purge a new fitting line until it has been tested and proven sound.

• Soundness tests must only be carried out using air or an inert gas in accordance with (relevant

version) AS/NZS5601. Never use oxygen or a fuel gas.

• Do not start purging until the purge area has been defined, made safe and cleared of all

sources of ignition.

• Do not smoke in or near the purge area.

• Do not apply a naked flame, for example a welding torch, to an existing fitting line until the

meter has been disconnected or spaded off and the installation has been fully purged of fuel

gas.



Note

The purging should be carried out safely and methodically in

accordance with (relevant version) AS/NZS5601 - Gas

Installations.

Purging a small volume gas installation

The (relevant version) AS/NZS5601 - Gas Installations, defines small volume installation as one with

a total installed pipe volume of up to 0.03 m3 (30 litres).

The pipe lengths given in the table below relate to an approximate volume of 0.03 m3.

Approximate pipe length (m) for a volume of 0.03 m3

Pipe material Nominal pipe size (mm)

18 20 23 25 32 40 50 63 80 90 100

Steel – 80 – 50 30 20 15 – 6 – 3.5

Copper – 130 – 70 40 30 16 – 7.5 – 4

PVC-U – 75 – 45 25 20 15 – 6 – 3.7

PE

(To AS 2718.1)

– 150 – – – 29 – 13 – 6 –

Polymide 153 – 88 – – 28 18 11 – 5.3 –


The type of purge for a small volume gas installation can depend on:

• whether the purge is commenced at an appliance (eg a cooking appliance) with an open burner

• whether the purge is carried out at an appliance fitted with an electronic flame safeguard

device

• whether the purge is carried out at an appliance fitted with a thermo-electric or bi-metallic

device.

See (relevant version) AS/NZS5601 - Gas Installations, for information on how to carry out purging in

the above situations.

Purging through an appliance fitted with an open burner

Carry out the purge as follows.

• Turn on one burner gas control until the presence of gas is detected. A change in the audible

tone and smell is a good indication that gas is at the burner.



• Let the gas flow for a few seconds longer, then turn off and allow sufficient time for any

accumulated gas to disperse before proceeding.

• Turn on one gas control valve again and keep a continuously burning flame at the burner until

the gas is alight and the flame is stable.

• Continue to purge until gas is available at each appliance.

Purging through an appliance fitted with a flame safeguard device

Where purging is to be carried out through this type of appliance, ensure the main burner gas control is

turned to the ‘OFF’ position before proceeding.

Electronic flame safeguard device fitted

Where an appliance is fitted with an electronic flame safeguard system, purging through the appliance

is difficult. Manual ignition cannot be achieved.

Carry out the purge as follows.

• Isolate the electrical supply to the appliance.

• Fit a bridging device (bonding strap) across the appliance inlet union connection.

• Slacken the union to allow gas to flow out, but do not fully disconnect it.

• Turn on the appliance manual shut-off valve (where fitted).

• As soon as the presence of gas is detected, tighten the union and test with soap and water

solution.

• Allow sufficient time for any gas to disperse.

Note

If the appliance is located in a confined space or small room,

particular care must be taken to ensure that all gas has dispersed

before activating the ignition source.

• Remove the bridging device (bonding strap).

• Turn on the power supply and activate the ignition source.

• Ignition may not be successful immediately and lockout may occur a number of times before

combustion is satisfactory.

• Allow sufficient time for any unburnt gas to disperse before re-setting the system.

Thermo-electric or bi-metallic device fitted

Where an appliance is fitted with one of these types of flame safeguard system, purging through a

pilot alone can be quite time consuming.



The purging time may be shortened by following this preliminary procedure.

• Fit a bridging device across the appliance inlet union connection.

• Slacken the union to allow gas to flow out, but do not fully disconnect it.

• Turn on the appliance manual shut-off valve (where fitted).

• As soon as the presence of gas is detected, tighten the union and test with soap and water

solution.

• Allow sufficient time for any gas to disperse.

Note

If the appliance is located in a confined space or small room,

particular care must be taken to ensure that all gas has dispersed

before an ignition source is applied.

• Remove the bridging device.

• Follow the normal appliance lighting sequence, applying a continuously burning flame to the

pilot.

Note

The use of a continuously burning flame may not be suitable

with some appliances, for example, balanced flue appliances.

Such appliances are normally fitted with an automatic ignition

source which may have to be activated a number of times

before successful ignition is achieved.

Note

Do not use an LP gas flame (or any other gas) for lighting

appliances because overheating can damage the thermocouple

lead or bi-metallic device.

• Continue to purge until the pilot flame remains alight and stable.

• Ensure the appliance main burner flame is stable and operates satisfactorily.

Electrical safety bonding or bridging

AS/NZS5601 - Gas Installations (relevant version) states where a metal pipe is to be cut, or an

appliance, component or fitting is to be disconnected from consumer piping, a suitable metallic

bridging device shall be installed across the intended cut or break to ensure electrical continuity. The

bridging device shall not be removed until all work is completed.



This means that if, during the purging process you intend to disconnect or loosen any union

connection, then an approved bridging device must be used. Any stray electrical current which may be

running through the pipe you are working on, will be able to flow around the disconnection.

Bonding straps

When purging through plastic piping it may be necessary to safeguard against static electricity. Refer

to (relevant version) AS/NZS5601 for a suitable method of discharging static electricity.

Note


accordance with Appendix D of (relevant version)

AS/NZS5601 - Gas Installations.

Worksheet


Purging a large volume gas installation

A large volume gas installation is one with a total installed pipe volume exceeding 0.03 m3.

A large volume gas installation should be purged to the outside atmosphere. The purge outlet should

be at least 6 m away from any ignition source and well clear of any opening into a building.



Note

The purging outlet should not exceed 25 mm nominal diameter.

Further details regarding purging of large volume gas installations should be obtained from the

authority before any work commences.


The purging requirements for a large volume gas installation includes the following.

• Checking the volume of consumer piping using the table below.

Approximate pipe length (m) for a volume of 0.03 m3

Pipe material Nominal pipe size (mm)

18 20 23 25 32 40 50 63 80 90 100

Steel – 80 – 50 30 20 15 – 6 – 3.5

Copper – 130 – 70 40 30 16 – 7.5 – 4

PVC-U – 75 – 45 25 20 15 – 6 – 3.7

PE

(To AS 2718.1)

– 150 – – – 29 – 13 – 6 –

Polymide 153 – 88 – – 28 18 11 – 5.3 –

• Selecting purge medium appropriate for the work and in accordance with (relevant version)

AS/NZS5601 - Gas Installations.

Purging a large volume gas installation using a purge stack

The recommended purging kit has been designed to assist in purging to the outside atmosphere. Care

should be taken in selecting suitable connections. ‘Kamlock’ type connections are recommended. The

hose diameter should be compatible with the purge stack; 25 mm is recommended. Smaller diameters

may result in a slow purge.

The kit should comprise:

• purge stack (approximately 2 m of DN 25 steel)

• sample hose

• purge bucket (with soap solution)

• purge hose

• valves and fittings

• combustible gas detector

• cylinder regulator, hose and fittings

• supply of nitrogen

• safety signs




Typical purging stack

It is advisable also to provide suitable ‘no smoking’ signs and witches hats to cordon off the selected

purge area. The purge area selected must ensure that there are no ignition sources within a distance of

at least 6 m.

The use of a flame trap is optional. If a flame trap is used, ensure that it is not unduly restrictive to the

flow of gas, and that it is cleaned prior to use. If a flame trap is not used, then the velocity of the

purging gas must be such that any light back is prevented.

Using the equipment to purge

Purging the meter

Prior to commencing any purge, check whether or not the meter has been purged. It is normally the

responsibility of the gas distribution company to purge the meter and set the meter regulator.

The amount of gas required to purge a meter is, for a diaphragm meter, five times the rated capacity

per revolution.

The capacity per revolution is shown on the meter badge.

For other meters, check the required purge amount with the local gas distributor. Use the test dial to

measure the purging volume required to completely purge the meter. Conversion: 0.01 m3 is 10 litres.



Purging the installation

1. Fit suitable pressure gauges and note the test dial position if the meter is to be purged.

2. Locate purge stack at furthest point on main run.

3. It is advisable to calculate the volume of the main run of pipe before commencing the purge.

Observe that volume passing through the purge stack.

4. Open the meter control valve slowly and ensure the maximum purging pressure is not

exceeded (refer to the table on page 13).

5. Slowly open the purge hose inlet and check the purge stack connections.

6. Slowly open the purge main valve. As this valve is opened, the sound of flowing gas should

be heard.

7. If necessary, increase the flowing pressure, ensuring the maximum purging pressure is not

exceeded.

8. Make sure the meter is fully purged.

9. Continue to purge through the purge stack until natural gas starts to emerge. This is often

evident by a change in the sound of the gas flowing out of the stack due to the difference in

densities of the gases.

10. Turn off the purge stack main valve when it is considered that gas is (or should be) flowing.

11. Take a sample from the purge stack sampling point by either:

− the detergent in water method

− a suitable gas detector (minimum acceptable reading 95% gas).

12. Continue purging and testing until a satisfactory result is obtained.

13. When the correct test result is obtained, continue purging for a further minute. The purge of

this section of the installation is now complete.

14. Slowly turn off the valves in this order:

• purge stack main valve

• meter control valve

• purge hose inlet valve.

15. Relieve pressure in the purge hose by opening the purge stack main valve and then close the

valve.

16. Disconnect purge hose and hose inlet valve from the installation capping off immediately to

avoid gas escaping and air re-entering the line.

17. Transfer the purge stack and hose to the end of the branch nearest the meter and repeat steps

three to sixteen.



18. Continue purging all branches, moving away from the meter, until the whole installation is

filled with gas.

19. Complete the purge by lighting appliances and checking that combustion is correct.

Gas sample test methods

Detergent in water method

1. Fill the purge bucket with a mixture of water and liquid detergent. If using a purpose made

bucket, fill to 50 mm above pipe outlet.

2. Connect bucket to purge stack sample valve

3. To take a sample of gas for testing, slowly open the sample valve. The gas will cause bubbles

to form in the purge bucket.

4. When sufficient bubbles have formed, turn off the sample valve and disconnect the bucket.

Ensure that any bubbles surrounding or adhering to the bucket are dispersed. The bubbles will

tend to rise when filled with gas, and lift off from the surface.

5. Carry the bucket to a safe place and carefully light the bubbles with an extended taper.

6. Observe what happens and make the associated interpretation.

Observation Interpretation

1. No ignition occurs • Too much air or inert gas still in the line.

• Continue purging

2. Ignition occurs with a

sharp cracking noise • Explosive air or gas mixture in the line.

• Continue purging

3. Ignition occurs quietly

and slowly • Gas in line.

• Purge complete.

7. Continue with steps three and four until observation 3 occurs.

Gas detector method

To take a gas sample, open the purge stack valve and insert the sampling probe. Draw the sample into

the gas detector. The minimum acceptable reading is 95% gas.



Note


accordance with of (relevant version) AS/NZS5601 - Gas

Installations.

Purging consumer piping of fuel gas

Where consumer piping is to be opened for alteration, repair or extension, the section involved should

be turned off from the supply at a convenient point and the piping vented to atmosphere. This should

make the pipeline safe to work on and minimise the chance of a dangerous situation.


Before the purging of fuel gas you need to check pipe length at which an inert gas purge is required.

If the section involved exceeds the length shown in the table below, the remaining fuel gas should be

displaced by an inert gas. Inert gas purging procedures can be obtained from the authority.

Pipe length at which an inert gas purge is required

Nominal pipe size (mm) Approximate pipe length (m)

50 25

65 15

80 10

100 5

150 3

Over 150 All



Replacing air or natural gas using nitrogen

Introduction

This procedure is suitable where it is required or preferable to use nitrogen to totally displace all the

air or natural gas that exists in a gas installation.

The procedure must be carried out where:

• any consumer piping being commissioned has a diameter exceeding 100 DN

• consumer piping, regardless of length or diameter, is being

de-commissioned and a hazard may be created, eg when welding or cutting into the line

• consumer piping, regardless of length or diameter, containing a vessel, eg a surge tank is being

commissioned or decommissioned.

Note

When extremely long consumer piping of any diameter is

involved (over 100 m), an inert purge should be carried out

prior to Purging Procedure No 1.

When part of the consumer piping is being taken out of service,

isolate the gas meter or the section of consumer piping not

being purged by means of an effective spade. The nitrogen

should be injected at that point.

Special care should be taken where vessels are involved.

Consider using an appropriate scientific company to assist in

planning the purge and to analyse the gas samples.

Important

When nitrogen purge is carried out, all branches on the section

involved, regardless of length or diameter, must be purged.

Volume of nitrogen required

The procedure for determining the volume of nitrogen required for a purge is as follows.

• Use the table below to determine the volume of pipe in a main run of consumer piping, ie.

from the meter to the furthest point.

• Determine the volume of nitrogen required if the meter is to be purged.

• Add the two values together and multiply by 1.5.

• Use the table below to determine the volume of pipe in each branch. Multiply each volume by

1.5.



Pipe volume (m3 per metre length)

Pipe diameter (DN)

Copper (Type B) to AS1432

Steel (Medium) to AS1074

Polythene (SDR 11) to AS/NZS4130

15 (PE) 0.0001 0.0002 0.0001

20 0.0002 0.0003 0.0002

25 0.0004 0.0006 0.0003

32 0.0006 0.0010 0.0005

40 0.0010 0.0014 0.0009

50 0.0018 0.0022 0.0012

65 (63 PE) 0.0030 0.0037 0.0022

80 (90 PE) 0.0040 0.0052 0.0043

100 (110 PE) 0.0075 0.0088 0.0064

125 0.0110 0.0130 0.0083

150 (160 PE) 0.0167 0.0190 0.0130

200 0.0310 0.0210

• Add together all volumes calculated in the first two steps. This gives the total volume of

nitrogen required to carry out the purge. Refer to the table below for the number of nitrogen

cylinders required (an extra cylinder may be ordered as a precaution).

Nitrogen cylinder volumes (full)

Cylinder size Cylinder volume (m3) (NTP)

D 1.3

E 3.2

G 6.4

Note

The cylinder pressure when full is approx 14 000 kPa.



Purging with nitrogen

The following installation is to be purged using the nitrogen system shown.

Nitrogen equipment

Installation to be purged using copper pipe



Main run (A – D) plus meter Branch (C – E)

Main run pipe volume = (A – B) + (B – C) + (C –

D)

Branch pipe volume = (C-E)

= (50 x 0.0167) = (30 x 0.0018)

+ (70 x 0.0075) = 0.054 m3

+ (35 x 0.0040) Multiply by 1.5 = 1.5 x 0.054 m3

= 0.835+0.525+0.14 Nitrogen required = 0.081 m3

= 1.5 m3

Meter volume

(For example) = 0.15 m3

Total amount of nitrogen required

Main run + meter = 1.65 m3 (A-D + meter) + (B-G) + (C-E)

Multiply by 1.5 = 2.5 m3 Total = 2.5+0.156+0.081

Nitrogen required = 2.73 m3

Branch (B-G)

Branch pipe volume = (B – F) + (F – G)

= (30 x 0.0040)

+ (20 x 0.0018)

= 0.12 + 0.036

= 0.08 m3

Multiply by 1.5 = 1.5 x 0.08 m3

Nitrogen required = 0.156 m3

Therefore, three size D cylinders or one size E cylinder is required. This allows some spare capacity.

Using only 0.13 m3 of the third size D cylinder will result in a pressure drop of 2000 kPa on the

cylinder gauge.



Cylinder pressure drop vs volume of nitrogen

Cylinder pressure drop (kPa)

Equivalent nitrogen volume in m3 (Normal temperature and pressure)

Size D cylinder Size E cylinder Size G cylinder

1000 0.09 0.23 0.46

2000 0.18 0.46 0.92

3000 0.27 0.69 1.38

4000 0.36 0.92 1.84

5000 0.45 1.15 2.30

6000 0.54 1.38 2.76

7000 0.63 1.61 3.22

8000 0.72 1.84 3.68

9000 0.81 2.07 4.14

10000 0.90 2.30 4.60

11000 0.99 2.53 5.06

12000 1.08 2.76 5.52

13000 1.17 2.99 5.98

14000 1.30 3.20 6.40

To ensure a complete purge, it is important that the whole consumer piping is filled with nitrogen. If

the meter as well as the piping is to be purged then the volume of nitrogen being injected into

consumer piping can be measured through the meter.

If this is not practical, for example when a section of consumer piping is being de-commissioned, then

the table below may be used.

Nitrogen set pressures

• The setting pressure of the cylinder regulator is 600 kPa.

• The second stage regulator is to be set to provide a flowing pressure of 3 kPa with a lock up

pressure of approximately 6 kPa.



Preparation for purge commences

Ensure that the purging and the inert gas equipment is correctly installed.

Ensure all valves are closed on:

• the cylinder and its hose

• the meter inlet

• all appliance isolating valves

• all branch valves

• the inlet to the purge hose

• the purge stack.

Worksheet




Carry out and test purge operation

After you have located a suitable outlet point for the purge gas, and have checked for ignition sources,

you can begin to purge the system. The purge should be carried out in a safe, methodical manner, and

considering other workers and or persons at the purge site.

• Record the reading of the gas meter to the nearest 1/100th of a cubic meter, or record the

reading of the cylinder pressure guage whichever is applicable.

• Set the cylinder outlet regulator to 600 kPa, and the second stage regulator to 6 kPa, to provide

a flowing pressure of 3 kPa.

• Slowly open the valve at the outlet of the line pressure guage.

• Check all connections and fittings between the nitrogen cylinder and the meter (consumer

piping) connection for leaks.

• Open purge hose and check purge stack connections for leaks.

• Slowly open the main valve on the purge stack. As this valve is opened the sound of flowing

gas should be heard. If desired, a manometer may be connected to the purge stack to

determine if flow is occurring.

• Continue purging until the required volume of nitrogen has been injected.

• Turn off the main valve on the purge stack.

Testing for completion of purge

When the purge is complete, you are required to test the system for correct functioning using test

equipment. The test data should be recorded in an appropriate format.

Commissioning

(air to nitrogen)

Field analysis to prove the completion of an air to nitrogen

purge is not practical. Therefore it is important to ensure

that a sufficient volume of nitrogen has been used for a

complete and successful purge.

De-commissioning

(gas to nitrogen)

In this case it can be proved that the fuel gas has been

eliminated. Use either the detergent in water method or a

suitable gas detector.

Detergent in water When an attempt is made to light the bubbles no ignition

must occur.

Gas detector Reading must be 0.5% gas (10% LEL) or less.

• On completion of purge, slowly turn off the valves in this order:

− main valve on purge stack

− cylinder regulator valve

− valve at line pressure guage

− purge hose inlet valve.



• Open the main valve at the purge stack to relieve purge pressure and then turn off the valve.

• Disconnect the purge hose inlet valve from the consumer piping and cap off quickly.

• Tranfer the purge hose and purge stack to the end of the branch nearest the meter and repeat

the procedure.

• Continue to purge the branches moving away from the meter until the whole consumer piping

is purged with nitrogen

• The procedure is now completed.

Note


accordance with (relevant version) AS/NZS5601 - Gas

Installations.



Clean up

On completion of the purging operation, all equipment, tools and test equipment are to be cleaned,

maintained where necessary and securely stored.

Waste materials must be disposed of appropriately and safely.

At the completion of the purging operation all equipment should be checked and repaired if necessary,

including gauges and valves. The equipment should be ready for use the next time it is required.

Specialised purging equipment including purge stack, purge bucket, hoses and fittings, should be

cleaned carefully and placed in containers to be stored in a safe secure place. All empty inert gas

cylinders should be stored ready for return to gas supplier. Full or partially full cylinders should be

stored in an upright position in an appropriate storage facility.

Cylinder gauges, hoses and associated fittings should be cleaned and stored in an appropriate storage

container away from heat and moisture.



Name:……….……………………………………………

Worksheet

CPCPGS3051A – Purge consumer piping

The student should complete this worksheet before attempting the practical installation.

The worksheet may form part of the assessment and should be checked and signed off by your trainer

or supervisor.

1. What does purging consumer piping mean?

2. Give five examples of where purging may be carried out.

3. What is the reason for purging consumer piping?



4. What are the definitions of small and large volume gas installations?

5. Why should the volume of vented methane gas be kept to a minimum?

6. List four gases which may be used as gas mediums for purging consumer piping.

7. When purging small volume gas installations, when should safety glasses be worn?



8. How many qualified persons should be on site, when purging a large volume gas installation

is carried out?

9. List four areas where valves should be closed, when preparing to purge using natural gas.

10. List four areas where valves should be closed, when preparing to purge using nitrogen.

11. What are warning signs used for when purging?



12. Define what a sub-meter is.

13. Using (relevant version) AS/NZS5601, what is the maximum length in metres of 25 mm

copper pipe for a volume of 0.03 m3?

14. What device must be used if a union connection is to be disconnected or loosened?

15. With the aid of a neat diagram describe a purge stack.



16. What is the amount of gas required to purge a diaphragm meter?

17. What does it mean if during detergent in water method of gas sampling, you light the bubbler

and observe that ignition occurs with a sharp cracking noise?

18. When a nitrogen purge is carried out, must all branches on the section be purged?

19. When purging with nitrogen, what should the cylinder regulator be set to?



20. Calculate the amount of nitrogen required for the following installation.

Copper pipe installed

Main run plus meter Branch

Main run pipe volume = Branch pipe volume =

= =

=

=

= =

=

Meter volume

(For example) =

Total amount of nitrogen required

Main run + meter =

Multiply by 1.5 = Total =

Nitrogen required =

Branch

Branch pipe volume = Therefore:

=

=

=

=

=

Trainer of supervisor’s signature:…….…………………………………..

Date of completion:………………………



Name:……………………………………………………

Practical application


Your trainer or supervisor will now work with you to demonstrate and explain the purging of

consumer piping.

The following points will be covered:

Design drawing or specification is obtained from job supervisor

WHS requirements associated with the purging of consumer gas piping systems, and the

workplace environment, are adhered to throughout the work

Quality assurance requirements for company operations are identified and adhered to

Work is planned in conjunction with others involved in, or affected by, the work

Appropriate tools and equipment for the conduct of the purging, including personal protective

equipment, are identified, selected and checked for serviceability

Work area and materials are prepared to support the efficient purging of the consumer gas

piping system

Installation is checked to ensure compliance with standards and relevant specifications

Volume of piping system is determined from design drawing and standards, recording

calculations in the format required by job specification

Method of purging is selected in compliance with standards and the authorities’ requirements

Purge medium is selected in compliance with standards, with calculations of the purge medium

volume being recorded in the format required by job specification

Outlet point for purge gas is located and the purge site is checked for ignition sources

Purge is carried out in accordance with standards or the authorities’ requirements

Completion of purge is verified by test equipment or recognized or approved workplace testing

procedures



Work area is cleared and materials disposed of or recycled in accordance with State or

Territory legislation and workplace procedures

Tools and equipment are cleaned, checked, maintained and stored in accordance with

manufacturers’ recommendations and workplace procedures

Documentation is completed in accordance with workplace requirements

On completion of this practical application you will be assessed. To prepare for your assessment make

sure you read the Assessment Checklist, the Assessment Task and Questions.

Trainer or Supervisor’s Signature:……………………………………………………..

Date of Completion:………………………………



Assessment checklist


Worksheet

Criteria Yes No

Have the worksheets been successfully completed?

Has the practical task been completed?

Are the job specification and local authorities’ or utilities’ requirements

available?

Trainer of Supervisor’s Signature:……………………………………………

Date of Completion:……………………………

Documents

© Commonwealth of Australia 2 - npstag.comnpstag.com/wp-content/uploads/2016/05/CPCPGS3051A... · Purge or purging ... Preparing to purge using nitrogen ... • job safety analysis