How To Purge A Gas Line Before Cutting

Gas information canvass 14: Purging Natural Gas Installation volumes betwixt 0.03 m3 to ane.0 m3

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Introduction

This information canvas has been prepared to aid gasfitters purge natural gas (NG) installations with volumes from 0.03 m³ to 1.0 m³ .

Note

For installation volumes upward to 0.03 thousand³ refer to Equally 5601: 2013, Appendix D Purging.

For installation volumes exceeding 1.0 thousandⁱⁱⁱ, purging may be based on this procedure but a Schedule viii submission, every bit shown in Gas Prophylactic (Gas Installation) Regulations 2008, describing the proposed testing and purging procedure must be provided to ESV for "complex gas installations" along with the ESV Start Piece of work and Compliance Find.

Purging

Purging is carried out to avoid the possibility of an explosive air/gas mixture existing or forming in consumer piping, appliances or confined spaces.

Purging is defined as:

• the displacement of air, or an inert gas, by a fuel gas; or
• the displacement of a fuel gas past air, or an inert gas.

Purging to displace air or inert gas with a combustible gas must accept place immediately following a successful gas tightness exam.

Notation: Nitrogen is the preferred inert gas for purging.

Purging involving LP Gas

Purging involving LP Gas requires alternate techniques. Refer to Appendix 3 at the cease of this document.

Installation volumes from 0.03 m³ to one.0 chiliad³

Because of concerns regarding the environmental impact of methane (a major component of natural gas) in the atmosphere, the amount of vented gas should be controlled and kept to a minimum.

Ensure that the pipe work is gastight and all open up ends are sealed before assuasive gas to enter.

The pressure created during purging should not exceed the design operating force per unit area, and must not exceed the pressure to which the pipe has been tested.

Pipe work being permanently taken out of service must be isolated physically past removing a section of pipe piece of work or by spading.

Decommissioned pipe work must be left purged with inert gas.

The purging of the billing meter is normally a thing for the gas distribution company.

Preparation before purging

A plan of the pipage work system must be available and its accurateness checked.

The purging process must exist planned carefully including the number of persons required to safely carry out the purge.

No other piece of work on the installation is to take place during the purging operation.

Purge points are to exist located at the finish of the main run and the end of each branch.

A gas detector capable of measuring all ranges, percentage LEL (lower explosive limit) to 100% gas will be required when purging to gas or from gas to an inert gas. (Minimum 95% gas required for consummate purge to gas).

NG is lighter than air and has a flammability range of between five% and 14% gas in air.

Site preparation

Exercise not commence purging until a purge area has been defined, made safe and has been cleared of all ignition sources (e.g. naked flames, airplane pilot lights, electrical switchgear and and then on). Also do not permit smoking in or most the purge area and utilise advisable signage to indicate this. Inform persons concerned that gas purging volition have identify.

A sufficient number of suitable fire extinguishers should exist provided and situated almost the venting point. Personnel should exist familiar with their utilize.

All electronic advice equipment must be intrinsically safe for apply in chancy areas.

Design and location of purging equipment

Purged gas should be vented to the outside temper and away from any buildings, air intakes or electric ignition sources. To do this, a purge stack or a purge saucepan may be required. Refer to Appendix 1 for a description of a typical purging kit.

Select a location where purged gases volition be dispersed quickly and volition not requite rising to complaints almost a olfactory property of gas.

Purging hoses must be suitable for containing the gas, be gastight and properly secured. Hose materials, such as polyethylene, could generate static electricity and must not be used.

ESV does non recommend the flaring of purged gases. If flaring is to be undertaken, special precautions such as the fitting of a flame arrester will be required.

Replacing air with natural gas
(Commissioning pipage work)

This procedure is suitable for use with consumer piping having a diameter of up to and including DN 100, provided that no vessels, such as surge tanks for gas engines, are involved.

This procedure as well applies to whatsoever consumer piping being commissioned for natural gas which has previously been purged with an inert gas.

Note: For piping lengths exceeding those listed in As 5601: 2013, Appendix D Tabular array D2, an Inert Gas Purge is required.

Purging a gas meter

On large commercial industrial installations, the meter is normally purged by the gas company. For small-scale meters or sub-meters allow 5 times the volume of gas held in the meter by observing the test dial. This will ensure that no trace of gas, air or inert gas remains inside the gas meter body. The cyclic capacity of a meter is shown on its badge plate.

Purging the installation

1. Calculate the book of the main run of pipe before commencing the purge (refer to Table i and the worked case in Appendix 2). Observing the volume passing through the meter will signal when gas is expected to menstruum through the purge stack or the purge saucepan.
2. Note the meter test punch position.
3. Connect the purge stack or the purge bucket to the furthest point on the primary run.
4. Open the control valves and commence the purge.
5. Ensure the maximum purging pressure is not exceeded.
6. Continue to purge through the purge stack or purge bucket until natural gas starts to emerge.
7. Have a sample from the purge stack or purge bucket sampling point using a suitable gas detector (minimum acceptable reading 95% gas). An indication that the purging of natural gas is nearing completion is seen when a mass of bubbles lift off and float away from the purge saucepan.
8. Continue purging and testing until an acceptable reading is obtained.
9. When the correct test outcome is obtained, the purge of this section of the installation will be complete.
10. Relieve the pressure in the purge hose past opening the purge stack chief valve.
11. Disconnect the purge hose and the hose inlet valve from the installation, capping off immediately to avoid gas escaping and air re-entering the line.
12. Transfer the purge stack or purge bucket and hose to the finish of the co-operative nearest the meter and repeat the procedure.
13. Continue purging all branches, moving away from the meter, until the whole installation is filled with gas.

Purging through an appliance

1. Plow on 1 burner until gas is detected.
2. Allow the gas flow for a few seconds, then plough off and allow time for accumulated gas to disperse.
3. Plow on one gas control valve again and apply a continuous burning flame at the burner until the gas is debark and the flame is stable.
4. Continue to purge each branch.

Purging through an appliance fitted with a flame safeguard organisation

1. Information technology may be necessary to break the appliance connection until gas is detected. This should be carried out in a controlled manner and with farthermost care. The employ of a bonding strap is advised.
2. When purging to an appliance with the flame safeguard requiring disconnection (from the appliance), intendance must be taken to prevent an accumulation of NG that could lead to an explosive mixture igniting. Purging to outside will ensure hazards are minimised.
3. When gas is detected, reconnect the appliance and permit time for any gas to disperse.
4. Follow the manufacturer's lighting instructions until ignition is successful and the apparatus is operating satisfactorily.

Replacing air or natural gas with an inert gas
(De-commissioning)

Where required, this procedure is suitable for totally displacing all air or natural gas from a gas installation.

Nitrogen is the preferred inert gas for purging.

This procedure must be carried out where:

• Any consumer piping being commissioned has a diameter exceeding those listed in As 5601: 2013, Tabular array D2.
• Consumer pipage, regardless of length or diameter, is being de-deputed and a hazard may exist created. For example when welding or cutting into the gas line.
• Consumer pipage, regardless of length or bore and containing a vessel (for case a surge tank), is being commissioned or de-commissioned.

Notes

• When role of the consumer piping is beingness 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 bespeak.
• Special intendance should exist taken where pressure vessels are involved. Consider using an appropriate specialist company to assist in planning the purge and to analyse the gas samples.
• For extremely big volume installations, where a full inert gas purge is non economically feasible, seek further advice from ESV prior to commencement of the purge.

Book of nitrogen required

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

1. Use Tabular array one in Appendix 2 to determine the volume of pipe in a main run of consumer piping, i.east. from the meter to the furthest signal and the book of pipe in each branch.
2. Add together together all volumes calculated in Step i and multiply by a factor of i.5. This gives the total book of nitrogen required to carry out the purge.
3. Refer to Table ii in Appendix 2 for the appropriate size of nitrogen cylinder required. (An extra cylinder may be ordered every bit a precaution).

Important

When a nitrogen purge is carried out all branches on the section involved, regardless of length or bore, must be purged.

Refer to Tabular array 3 in Appendix 2 to calculate the volume of nitrogen by pressure drop when purging smaller volumes of co-operative piping piece of work.

Nitrogen set pressures

The setting force per unit area of the cylinder regulator is 600 kPa.

The second stage regulator is to be ready to provide a flowing pressure of 3 kPa with a lock up force per unit area of approximately vi kPa.

Preparation before purging

Ensure that the purging and inert gas equipment is correctly installed and that all valves are closed.

Purging the installation

1. Record the reading of the cylinder pressure gauge.
2. Slowly open the valve at the outlet of the line pressure gauge.
3. Leak test all connections and fittings between the nitrogen cylinder and the consumer piping. Open the valve to purge the hose and check the purge stack connections for leaks.
4. 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 decide if gas flow is occurring.
5. Continue purging until the required volume of nitrogen has been injected.
6. Plough off the chief valve on the purge stack.
7. Disconnect the purge hose and the hose inlet valve from the installation, capping off immediately to avoid gas escaping and air re-entering the line.
8. Transfer the purge stack and hose to the end of the branch nearest the meter and repeat the procedure.
9. Continue purging all branches, moving away from the meter, until the whole installation is filled with gas.

Testing for completion of purge

Commissioning (air to nitrogen)

Field analysis to bear witness 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)

Gas Sample Test Method: Utilise a suitable gas detector able to read 0.five% gas (x% of LEL) or less to ensure the fuel gas has been eliminated.

Annotation: NG has a flammability range between v% and 14% gas in air.

Further information

For further information about purging contact the Gas Technical helpline on 1800 652 563.

Appendix i

Recommended purging kit

The recommended purging kit, shown here, has been designed to aid in purging to the exterior atmosphere.

The hose diameter should exist uniform with the purge stack; 25 mm is recommended. Smaller diameters may result in a slower purge.

Poly pipe should be avoided as it may exist subject to sparking from static electricity.

It is advisable besides to provide suitable 'NO SMOKING' signs and witches hats to cordon off the purge area. There must be no ignition sources inside 6 g of the purge area.

The use of a flame arrester is optional. If a flame arrester is used, ensure that it is not unduly restrictive to the menstruum of gas and that it is cleaned prior to use. If a flame arrester is not used, and so the velocity of the purging gas must be such that any "calorie-free dorsum" is prevented.

If further information is required, please phone the Gas Technical helpline on 1800 652 563.

Appendix two

Tabular array i – Pipe volume (m³ per metre length)

Pipe diameter (DN)	Copper (Blazon B) to Equally 1432	Steel (Medium) to AS 1074	Polyethylene (SDR xi) to Equally 4130	UPVC Class 100 Types 1, ii, & iii to Every bit 1464
xv (xvi 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
xl	0.0010	0.0014	0.0009	0.0013
50	0.0018	0.0022	0.0012	0.0021
65 (63 PE)	0.0030	0.0037	0.0022
80 (xc PE)	0.0040	0.0052	0.0043	0.0050
100 (110 PE)	0.0075	0.0088	0.0064	0.0084
125	0.0110	0.0130	0.0083
150 (160 PE)	0.0167	0.0190	0.0130	0.0172
200	0.0310		0.0210

Table 2 – Nitrogen cylinder volumes (total)

Cylinder Size	Cylinder book (mthree) (NTP)
D	1.iii
Eastward	iii.two
G	6.iv

Table 3 – Cylinder pressure drib Vs Volume of nitrogen

Cylinder Pressure level Drib (kPa)	Equivalent nitrogen volume in thouthree (Normal temperature and pressure)
	Size D Cylinder	Size E Cylinder	Size One thousand Cylinder
i 000 2 000 3 000 4 000 5 000 6 000 7 000 viii 000 9 000 10 000 eleven 000 12 000 13 000 14 000	0.09 0.xviii 0.27 0.36 0.45 0.54 0.63 0.72 0.81 0.90 0.99 one.08 1.17 1.30	0.23 0.46 0.69 0.92 i.15 1.38 1.61 ane.84 2.07 2.30 2.53 2.76 2.99 3.20	0.46 0.92 one.38 1.84 ii.30 2.76 3.22 3.68 4.14 4.threescore five.06 5.52 v.98 half dozen.40

Case for calculating the total book of nitrogen required to purge the gas pipe network below (Refer to Tables 1, 2 and iii).

Example using copper pipe

(Refer to Tabular array i)

Main run (A-D)

Master run pipe volume = (A-B) + (B-C) + (C-D)
= (50 x 0.0167) + (lxx 10 0.0075) +
(35 x 0.0040)
= 0.835 + 0.525 + 0.140
= 1.500 mⁱⁱⁱ
Book of nitrogen for the primary run (A-D)
= 1.500 x 1.5 = 2.250 m³

Branch (B-Thousand)
Branch pipe volume = (B-F) + (F-One thousand)
= (twenty ten 0.0040) + (15 ten 0.0018)
= 0.080 + 0.027
= 0.107 one thousand^three
Volume of branch (B-1000)
= 0.107 ten 1.5 = 0.161 kⁱⁱⁱ

Branch (C-E)
Branch piping volume = (C-E)
= (20 X 0.0018)
= 0.036 mⁱⁱⁱ
Volume of branch (C-Eastward)
= 0.036 ten i.5 = 0.054 m³

Total amount of nitrogen required
(A-D) + (B-G) + (C-East)
= two.250 + 0.161 + 0.054
= 2.465 m³

Therefore co-ordinate to Tabular array 2, two size
D cylinders, or i size E cylinder, would exist required. This allows some spare capacity.

Determining corporeality of nitrogen used

To ensure a complete purge, it is important that the whole consumer piping is filled with nitrogen. To purge the previous case, a total of 2.465 m³ of nitrogen is required. If
Size D cylinders are used, 2 total cylinders volition provide 2.6 thousandⁱⁱⁱ. See Table 2.

Referring to Table 3, for a Size D cylinder, 0.18 grand³ is equivalent to a pressure level drib of almost 2000 kPa on the cylinder estimate. This allows the correct volume of nitrogen to be calculated for each branch.

Appendix three

Purging LPG

Note: This data is to exist used in conjunction with the procedures outlined for purging natural gas.

When purging LP Gas special consideration must be given to the increased hazards involved.

A risk cess should exist carried out to identify special hazards associated with purging LP Gas.

Notation: LPG is a heavier than air gas and has a flammability limit of between 2% and 10% gas in air.

Gas Sample Exam Method

Purging LP Gas to inert gas:

Apply a suitable gas detector able to read 0.2% gas (ten% of LEL) or less to ensure the fuel gas has been eliminated.

Alert

Special care is to be taken to ensure that LP Gas, which is heavier than air and accumulates in low places, is fully dispersed before applying an ignition source. Do not purge into a combustion chamber or other confined space.

For an open up air purge using LP Gas consideration needs to exist given to:

• Proximity of purge gas to potential ignition sources.
• Drains and openings into buildings such every bit doors, wall vents, air intakes and then on.
• Ensuring that the surface area is sufficient to permit effective ground level dispersion.
• Checking the prevailing air current direction.
• Identifying low areas; the gradient of the purge area needs to be taken into business relationship to ensure gas volition not accrue in a bars expanse.

It is recommended that a purge stack exist used to allow a more effective dispersion of gas and a gas analyser should be used to ensure a complete purge is achieved safely (minimum 95% gas).

When an open air purge is not practical it may be advisable to apply a gas flare in conjunction with a gas analyser.

If a flare is to exist used a Schedule eight submission, equally shown in Gas Rubber (Gas Installation) Regulations 2008, describing the purge procedure and purge equipment must be provided to ESV for
approval prior to commencement of the purge. A flame trap or arrester is required when using a flare.

Purging to an apparatus fitted with a flame safeguard device may crave disconnection of the appliance. Care must be taken to prevent an accumulation of LP Gas which could lead to an explosive mixture igniting. Purging to outside will ensure hazards are minimised.

Purging through an appliance burner should exist done with a continuous flame positioned at the burner to ensure no hazardous LPG gas accumulation can result.

Farther data

For further information contact Gas Safety Technical Information on 1800 652 563 and select option 3 or e-mail gastechnicalenquiry@energysafe.vic.gov.au.

Source: https://esv.vic.gov.au/gas-technical-information-sheets/14-purging-natural-gas-installation/

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