IGEM-UP-1C Draft for Comment - 2nd Consultation (IGEM-TSP-10-122)

INSTITUTION OF GAS ENGINEERS AND MANAGERS

IGEM/UP/1C Communication XXXX

IGEM/TSP/10/122

Founded 1863 Royal Charter 1929 Patron Her Majesty the Queen

STRENGTH TESTING, TIGHTNESS TESTING AND DIRECT PURGING OF NATURAL GAS AND PROPANE METER INSTALLATIONS DRAFT FOR COMMENT 1

This draft Standard IGEM/UP/1C has been prepared by a Panel under the chairmanship of Dave Blackburn.

2

This Draft for Comment is presented to Industry for comments which are required by 21st May 2010, and in accordance with the attached Reply Form.

3

This is a draft document and should not be regarded or used as a fully approved and published Standard. It is anticipated that amendments will be made prior to publication. It should be noted that this draft Standard contains intellectual property belonging to IGEM. Unauthorised copying or use by any unauthorised person or party is not permitted.

4

This is a copyright document of the Institution of Gas Engineers and Managers. Enquiries should be addressed in the first instance to: Nick Cowling IGEM IGEM House 26-28 High Street Kegworth Derbyshire, DE74 2DA Tel: 0844 375 4436 Fax: 01509 678198 Email: [email protected]

IGEM/UP/1C Draft for Industry Comment (2nd Consultation) Since IGEM/UP/1C was last issued for Comment (9th March 2009) the Panel has responded to the Comments received and made changes where appropriate. In addition to this, the Panel made other amendments to the document including changing the scope. Therefore the Standard is being re-issued for Industry Comment. To assist with this 2nd Consultation, a summary of the amendments is given below. Section 2 – Scope Clause 2.1 New. Inclusion of propane meter installations. Note: Butane is not included as its use is normally limited to cylinders.

Clause 2.3 Amended. Rewording of when Strength/tightness Tests are required. Clause 2.8 New. IGEM/UP/1C adopts the concept of Gauge readable movement and but accepts that the concept of ‘No perceptible movement’ can be used. Figure 3 New. Inclusion of typical installation diagrams. Section 4 – Strength Testing Sub-Sections 4.1 to 4.2 New. Guidance on when and how to carry Strength Tests. Sub-Section 4.3 and Figures 4(a) to (g) New. Information for testing installations with a pressure break. Tables 1 to 4 New. Example STP values for Natural Gas and Propane installations. Table 5 - Selection of Strength test duration Amended. The values given have been simplified. Table 6 – Safety distances Amended. The values given have been simplified. Section 5 – Tightness Testing Sub-Section – 5.1 New. Further information on when a tightness test is carried out has been included. Sub-Section 5.2 Amended. Removal of New and Existing procedures. All installations are now covered by one procedure. Sub-Section 5.3 and Figures 6(a) to (c) New. Information for testing installations with a pressure break. Sub-Section 5.4 and Tables 7, 8, 9 – Tightness test durations Amended. Test times have been provided. The calculation method for TTD has been moved to Appendix 4. Sub-Section 5.5.4 Amended. Removal of existing and new installation procedures, just one procedure provided. Figure 7 and 8 Amended. Flowcharts given for testing with Fuel Gas and Nitrogen. Appendix 5 New. Inclusion of risk assessment for purging heavier than air gases.

Organisations to which this Draft for Comment has been issued: • Association of Independent Gas Transporters (AIGT) • Association of meter operators (AMO) • British Standards Institution (BSI) • Chartered Institute of Building Services Engineers (CIBSE) • Chartered Institute of Heating and Plumbing Engineers (CIHPE) • Construction Industry Training Board (CITB) • Council for Registered Gas Installers (CORGI) • Distribution Network Owners • Energy Institute • Gas Industry Safety Group (GISG) • Gas Safe Register • Health and Safety Executive (HSE) • National Grid • National Grid Metering • Northern Gas Networks • Office of Gas and Electricity Markets (OFGEM) • Ofgem MAMCOP Management Board • Scotiagas Networks • Society of British Gas Industries (SBGI) • The Gas Forum • Wales and West Utilities • UKLPG • IGEM Committees and Panels


Strength testing, tightness testing and direct purging of Natural Gas and Propane meter installations Draft for Comment (2nd Consultation)

Founded 1863 Royal Charter 1929 Patron: Her Majesty the Queen


Strength testing, tightness testing and direct purging of Natural Gas and Propane meter installations Draft for Comment (2nd Consultation)

Price Code: XXX © The Institution of Gas Engineers and Managers IGEM House High Street Kegworth Derbyshire, DE74 2DA Tel: 0844 375 4436 Fax: 01509 678198 Email: [email protected]

Copyright © 2010, IGEM. All rights reserved Registered charity number 214001 All content in this publication is, unless stated otherwise, the property of IGEM. Copyright laws protect this publication. Reproduction or retransmission in whole or in part, in any manner, without the prior written consent of the copyright holder, is a violation of copyright law. ISBN 978 1 905903 XX X ISSN 0367 7850 Published by the Institution of Gas Engineers and Managers Previous Publications: There are no previous publications. For information on other IGEM Standards please visit our website, www.igem.org.uk

IGEM/UP/1C – Draft for Comment (2nd Consultation)

CONTENTS SECTION

PAGE

1

Introduction

1

2

Scope

4

3

Legal and allied considerations

6

4

Strength testing

7

5

6

    

4.1

Decision whether to strength test

7

4.2

Strength test methodology

7

4.3

Determination of MOP and MIP

8

4.4

Method, pressure, duration and test criteria for strength testing

12

4.5

Procedures

12

Tightness testing

16

    

5.1

Decision whether to tightness test

16

5.2

General

16

5.3

Determination of TTP

17

5.4

Tightness test duration (TTD)

18

5.5



Procedures – tightness testing  5.5.1 By-passing components  5.5.2 Ambient conditions  5.5.3 Section and valve isolation  5.5.4 Testing

19 19 19 19 19

5.6

Completion

20

Direct purging

24

  

6.1

General

24

6.2

Planning and supervision

24

6.3

   

Site precautions  6.3.1 Warning notices and labels  6.3.2 Electrical and fire

25 25 25

6.4

Designing and positioning purge points, hoses and vent stacks

26

6.5

Verification of purge velocity

27

6.6

Identification of purge gas cylinders

27

6.7



Gas detectors, oxygen measuring devices and other electronic equipment

27

6.8

 

Determination of the purge volume, minimum purge flow rate and purge time

28

6.9

Vent gas testing

29

6.10

Purging procedures  6.10.1 Direct purging from air to gas i.e. commissioning  6.10.2 Direct purging from gas to air i.e. de-commissioning

29 29 31

IGEM, IGEM House, High Street, Kegworth, Derbyshire, DE74 2DA. Website igem.org.uk.


APPENDIX 1

Glossary, acronyms, abbreviations, units, subscripts and symbols

35

2

References

37

3

Indirect purging with nitrogen

39

4

Calculation of tightness test duration

41

5

Purging heavier-than-air gases – risk assessment

44

1

Algorithm to select testing and purging standards

2

2

Relative pressure levels

2

3

Typical schematic meter installations

5

4

Pressure breaks. Strength requirements

5

Flowchart/decision algorithm for strength testing

6

Pressure breaks. Tightness test requirements

7

Flowchart/decision algorithm for tightness testing with air or Nitrogen

21

8

Flowchart/decision algorithm for tightness testing with fuel gas

22

9

Flowchart for direct purging of air to gas

33

10

Flowchart for direct purging of gas to air

34

1

Example 1. A low pressure outlet fed from a low pressure network (NG)

11

2

Example 2. A low pressure outlet fed from a medium pressure network (NG)

11

Example 3. A low pressure outlet fed from a low pressure network (Propane) - BS 3016 regulators

11

4

Example 4. A low pressure outlet fed from a medium pressure network (Propane) - BS 3016 regulators

11

5

Selection of the method, pressure, duration, and the test criteria for strength testing

12

Safety distances each side of an installation for strength testing at STP exceeding 1 bar

13

7

Tightness test duration for typical installations and using a pressure gauge with a GRM of 0.5 mbar

20

8

Calculated tightness test durations (mins) for RD and turbine meters using a gauge with a GRM of 0.5 mbar (Natural Gas)

23

FIGURES

9-10 15 17-18

TABLES

3

6



9

Calculated tightness test durations (mins) for RD and turbine meters using a gauge with a GRM of 0.5 mbar (Propane)

23

10

Minimum purge flow rate and velocity with recommended minimum purge point, associated vent and flare stack dimensions

29

11

Flammability limits and safe purge end points

29

12

Minimum quantity of nitrogen per 1 m length of pipe

39

13

Flammability limits and safe purge end points for inert purge

40

14

Installation volume (IV) of meters

41

15

Volume of 1 m length of pipe

42

16

Selection of pressure gauges (typical data)

42

17

Factor F1 to apply when calculating TTD

43



SECTION 1 : INTRODUCTION 1.1

This Standard has been drafted by an Institution of Gas Engineers and Managers (IGEM) Panel, appointed by IGEM’s Gas Utilization Committee, and has been approved by IGEM’s Technical Co-Ordinating Committee on behalf of the Council of IGEM.

1.2

It is necessary to check the scope of referenced standards given below. Figure 1 shows the most suitable Standard for a particular situation. IGEM/UP/1C deals with strength testing, tightness testing and direct purging of meter installations (as defined in IGEM/G/1), containing either Natural Gas (NG) or Propane, of volume not exceeding 1 m3 and MOP not exceeding 7 bar. IGE/UP/1 Edition 2 deals with all aspects of strength testing, tightness testing and direct purging of selected 1st, 2nd and 3rd family gases. For example, for NG, it covers pipework downstream of the emergency control valve (ECV) of maximum operating pressure (MOP) not exceeding 16 bar. IGE/UP/1A Edition 2 deals with strength testing, tightness testing and direct purging of NG installations of volume not exceeding 1 m3 and diameter not exceeding 150 mm, of MOP (and operating pressure (OP)) not exceeding 40 mbar and supply MOP not exceeding 75 mbar. IGE/UP/1B Edition 2 deals with tightness testing and purging of NG installations of volume not exceeding 0.035 m3, capacity not exceeding 16 m3 h-1, diameter not exceeding 35 mm, OP not exceeding 21 mbar and supply MOP not exceeding 2 bar. Note:

At the time of publication, it is anticipated that IGEM/UP/1B Edition 3 will cover LPG.

BS 5482-1 deals with tightness testing of domestic-sized liquefied petroleum gas (LPG) pipework (volume not exceeding 0.02 m3). For greater volume, IGE/UP/1 Edition 2 applies. Note:

See above regarding LPG in IGEM/UP/1B Edition 3.

If it is preferred (it is not recommended, as it is more complex to follow) IGE/UP/1 Edition 2 can be used rather than IGE/UP/1A Edition 2, IGE/UP/1B, IGEM/UP/1C or BS 5482-1. If IGE/UP/1A Edition 2 or IGE/UP/1B Edition 2 or IGEM/UP/1C or BS 5482-1 are not indicated, then it is essential that IGE/UP/1 Edition 2 is used. At the time of publication, neither IGE/UP/1B Edition 2 nor BS 5482-1 require strength testing.

1 IGEM, IGEM House, High Street, Kegworth, Derbyshire, DE74 2DA. Website igem.org.uk.


START

NATURAL GAS OR PROPANE METER INSTALLATION?

MOP 7 bar AND V 1 m3 AND no PE included AND isolated at outlet of the meter installation?

YES

NO

NATURAL GAS INSTALLATION?

IGEM/UP/1C

NO Supply MOP 2 bar AND OP 21 mbar AND Ø 35 mm AND meter capacity 16 m3 h-1 AND V 0.035 m3?

YES

YES

IGE/UP/1B EDITION 2

NO

NO

LPG INSTALLATION?

YES

YES

Ø 28 mm AND V 0.02 m3?

NO

YES

BS 5482-1

NO

OP and MOP 40 mbar AND supply MOP 75 mbar AND V 1 m3 AND Ø 150 mm?

YES

IGE/UP/1A EDITION 2

NO IGE/UP/1 EDITION 2

FIGURE 1 - ALGORITHM TO SELECT TESTING AND PURGING STANDARDS 1.3

“MOP” and other new terms such as “maximum incidental pressure” (MIP) and OP have been introduced to reflect gas pressure terminology used in European standards. IGEM/G/4 defines these terms and IGE/GM/8 Part 1 explains them in greater detail. Referring to Figure 2, note how OP is shown to oscillate about the set point (SP). Note also that MOP can be declared at any value from OP upwards to a limit below MIP. The strength test pressure (STP) has to be at least 110% MIP and in many cases (see Table 5) will be greater.

STP MIP OP MOP SP Note:

= = = = =

Strength test pressure Maximum incidental pressure (for example, as declared by the GT/MAM) Operating pressure Maximum operating pressure Set point of the regulator.

This is extracted from IGE/TD/13 and simplified for the purposes of IGEM/UP/1C.

FIGURE 2 - RELATIVE PRESSURE LEVELS 2 IGEM, IGEM House, High Street, Kegworth, Derbyshire, DE74 2DA. Website igem.org.uk.


1.4

This Standard makes use of the terms “should”, “shall” and “must” when prescribing particular requirement. Notwithstanding Sub-Section 1.7:



the term “must” identifies a requirement by law in Great Britain (GB) at the time of publication



the term “shall” prescribes a requirement which, it is intended, will be complied with in full and without deviation



the term “should” prescribes a requirement which, it is intended, will be complied with unless, after prior consideration, deviation is considered to be acceptable.

Such terms may have different meanings when used in legislation, or Health and Safety and Executive (HSE) Approved Code of Practice (ACoPs) or guidance, and reference needs to be made to such statutory legislation or official guidance for information on legal obligations. 1.5

1.6

The primary responsibility for compliance with legal duties rests with the employer. The fact that certain employees, for example “responsible engineers”, are allowed to exercise their professional judgement does not allow employers to abrogate their primary responsibilities. Employers must:



have done everything to ensure, so far as it is reasonably practicable, that “responsible engineers” have the skills, training, experience and personal qualities necessary for the proper exercise of professional judgement



have systems and procedures in place to ensure that the exercise of professional judgement by “responsible engineers” is subject to appropriate monitoring and review



not require “responsible engineers” to undertake tasks which would necessitate the exercise of professional judgement that is not within their competence. There should be written procedures defining the extent to which “responsible engineers” can exercise their professional judgement. When “responsible engineers” are asked to undertake tasks which deviate from this they should refer the matter for higher review.

It is now widely accepted that the majority of accidents in industry generally are in some measure attributable to human as well as technical factors in the sense that actions by people initiated or contributed to the accidents, or people might have acted in a more appropriate manner to avert them. It is therefore necessary to give proper consideration to the management of these human factors and the control of risk. To assist in this, it is recommended that due regard be paid to HSG48.

1.7

Notwithstanding Sub-Section 1.4, this Standard does not attempt to make the use of any method or specification obligatory against the judgement of the responsible engineer. Where new and better techniques are developed and proved, they should be adopted without waiting for modification to this Standard. Amendments to this Standard will be issued when necessary, and their publication will be announced in the Journal of the Institution and other publications as appropriate.

1.8

Requests for interpretation of this Standard in relation to matters within its scope, but not precisely covered by the current text, should be addressed in writing to Technical Services, IGEM, IGEM House, High Street, Kegworth Derbyshire, DE74 2DA and will be submitted to the relevant Committee for consideration and advice, but in the context that the final responsibility is that of the engineer concerned. If any advice is given by or on behalf of IGEM, this does not relieve the responsible engineer of any of his or her obligations.

1.9

This Standard was published in June 2010.



SECTION 2 : SCOPE 2.1

This Standard applies for any meter installation (as defined in IGEM/G/1 and IGEM/G/4) or section of a meter installation:



supplying Natural Gas or propane Note:

    

This Standard does not cover Butane as its use is normally limited to cylinders.

of MOP  7 bar of volume not exceeding 1 m3 having a method of temporarily sealing the outlet of the installation/section, for example a valve, blanking device, etc. not including polyethylene (PE) pipe or fittings which is not within scope of IGE/UP/1B.

Note 1: The diversity of meter installations is such that it is inappropriate to provide detailed guidelines for all types of installation covered by the scope of this Standard. It is recognised that special circumstances may occur, on a meter installation, for which some of the requirements in this Standard cannot be applied. In such a case, IGE/UP/1 applies and the procedure needs to be developed by personnel of adequate competency and experience. Certain “legacy” meter installations do not comply with the Standard arrangements given in IGEM/G/1. The principles of this Standard may be applied to the majority of such legacy installations. Note 2: “Meter installation or section of a meter installation” is hereafter referred to as “installation”.

2.2

This Standard covers pneumatic strength testing and tightness testing, and direct purging. It does not address hydrostatic testing.

2.3

This Standard covers strength testing and/or tightness testing in the following circumstances:

   

prior to a new installation being commissioned with gas, where a leak is suspected to exist on an existing installation, where a new section has been added into an existing installation, where there has been a complete loss of pressure, for any reason, for example component replacement, section replacement, etc.

Typical schematic installations are shown in Figure 3. 2.4

This Standard covers direct purging in the following circumstances:

  

new installation alteration to, replacement of, or re-use of, an existing installation where there has been a complete loss of pressure for any reason Note: The closure of a valve, for example the ECV, can result in a complete loss of pressure which necessitates tightness testing and purging before resumption of supply.

 

where there is the possibility of air being present in an installation where an installation is to be taken temporarily or permanently out of service.

2.5

All pressures quoted are gauge pressures unless otherwise stated.

2.6

Italicised text is informative and does not represent formal requirements.

2.7

Appendices are informative and do not represent formal requirements unless specifically referenced in the main sections via the prescriptive terms “should”, “shall” or “must”.



2.8

IGEM/UP/1C adopts the concept of “Gauge readable movement” (GRM). When using a water gauge, it may be possible to reduce the duration of tests by adopting the concept of “no perceptible movement”.

M M Downstream system kept pressurised

M Downstream system kept pressurised

M Downstream system kept pressurised

M

M

M

M FIGURE 3 - TYPICAL SCHEMATIC METER INSTALLATIONS



SECTION 3 : LEGAL AND ALLIED CONSIDERATIONS 3.1

This Standard is set out against a background of legislation in force in GB at the time of publication. Similar considerations are likely to apply in other countries where reference to appropriate national legislation is necessary. All relevant legislation must be applied and relevant ACoPs, official Guidance notes and referenced codes, standard, etc. shall be taken into account. Where standards are quoted, equivalent national or international standards etc. equally may be appropriate. Unless otherwise stated, the latest version of the referenced document should be used.

3.2

Any person engaged in strength testing, tightness testing or purging of pipework must be a competent person. Note:

Any person carrying out the installation of gas pipework and associated fittings must be competent to do so. Where gas installation work is carried out in properties covered by the current Gas Safety (Installation and Use) Regulations (GS(I&U)R), the persons carrying out that work must be a “member of a class of persons” as specified by those Regulations. Persons who are deemed competent to carry out gas work under GS(I&U)R are those who hold a current certificate of competence in the type of activity to be conducted issued under aligned SN/NVQ arrangements, or by a certification body accredited by the United Kingdom Accreditation Service (UKAS) for the Nationally Accredited Certification Scheme (ACS).

3.3

Consideration shall be given to the environmental impact of methane and other hydrocarbons in the atmosphere.

3.4

In the following situations, any electronic equipment used shall be certified for use in a hazardous area:



when seeking the source of a known or suspected gas leak, using a gas detector



when a hazardous area is imposed by another installation, for example an oil supply, and the equipment is to be used within that area



when a risk assessment indicates that use of uncertified equipment is not acceptable (see below)



when it is anticipated that the area in which the equipment will be located will be left unattended at any time during the test/purge.

The decision on whether electronic equipment, for example pressure gauges and gas detectors, can be of a type not certified for use in a hazardous area, may be complex and is not an issue that can be developed in IGEM/UP/1C. However, unless the pipework being tested or purged is known to contain only air and/or inert gases (in which case equipment that is not certified may be used) any use of such uncertified equipment shall be subject to a suitable risk assessment prior to use. Equipment manufacturers’ instructions may assist in this risk assessment. Note 1: For lower pressures, water gauges can always be used if there is any doubt about the use of uncertified gauges. Note 2: For MOP  75 mbar, use of uncertified gauges placed in the open air and located at least 150 mm from any potential gas source (a greater clearance may be required) may be acceptable although it is still possible for a hazardous area to apply, particularly as imposed by another installation. Note 3: Further guidance on hazardous area classification is available in IGEM/GM/7B.



SECTION 4 : STRENGTH TESTING Some leak detection fluids (LDFs) have an adverse effect on certain installation materials. Consequently, any residual fluid shall be washed off thoroughly and subsequently dried. LDFs containing more than 30 parts per million of halogens shall not be used on stainless steel components. If necessary, for example when joints will be broken, temporary electrical continuity bonds shall be installed before testing. Where an installation contains fuel gas, it has to be purged to nitrogen or air before strength testing. 4.1

DECISION WHETHER TO STRENGTH TEST

4.1.1

A strength test shall be carried out on any new or replacement installation (or part thereof) except for components that have been pre-tested or have been removed to avoid over pressurisation, for example regulators and meters.

4.1.2

Where the meter installation is pre-assembled and fully tested by the manufacturer; comes complete with documentation and has not been modified or altered in any way, there is no need to carry out a strength test on the assembly. A tightness test shall be carried out (See Section 5).

4.1.3

Where a meter installation is assembled from components (screwed or bolted together), all of which have been fully tested by the manufacturer; are delivered complete with documentation and have not been modified or altered in any way, there is no need to carry out a strength test on the assembly. A tightness test shall be carried out (See Section 5). Note:

Where a component or sub-assembly (meter installation component, meter “skid” unit, etc.) has been pre-tested and not subsequently modified (such as by cutting threads or welding) and has appropriate certificates of conformity available, the strength testing of such a component/assembly need not be undertaken but a visual examination of joints, general condition, suitability, etc. is recommended prior to installing and subsequent tightness testing as for a new installation. Permanent marking, for example by manufacturer’s badging/stamping, may be deemed as certification of conformity.

4.1.4

A strength test should not be carried out on an existing installation unless the installation has been subjected to repairs involving forming pipes, welding, or new components that have not been pre-tested separately, or OP is to be increased to a level not previously covered by strength testing.

4.2

STRENGTH TESTING METHODOLOGY Where an on-site strength test is required it is recommended that either;



the replacement components are strength tested separate from the installation, or,



the strength test is carried out concurrently with the tightness test. This would mean carrying out the tightness test at STP, applying the greater of the required stabilization and test times but not both, and applying the tightness test pass/fail criteria (a pass indicating that both the strength and tightness tests are satisfactory). However, there will be a minority of installations that will fail the tightness test that would have passed if the tests had been carried out separately or simply combined.



4.3

DETERMINATION OF MOP AND MIP

4.3.1

The majority of meter installations will incorporate a pressure regulator and, as such will normally incorporate a pressure break. The pressure break is a point in the installation defined by the designer, either side of which a different strength test pressure is applied. The location of the pressure break will vary depending on the provision of valves and the characteristics of the upstream Network and downstream consumers’ system. Typically, the pressure break will be the outlet of the first valve downstream of the pressure regulator, (see Figures 4(a) and 4(b)). However, in a small number of installations where the consumers’ system has the ability to subject the meter installation to a higher reverse pressure under fault conditions (MIPc), the pressure break will be on the inlet to the first safety device (see Figures 4(c) and 4(d)). Where the information available on site indicates that the pressure break is not located as shown in Figure 4, this shall be taken into account. The values of STP shall be determined for the different sections of pipework to be tested.

4.3.2

Where different parts of an installation have different DPs, MIPs, etc., the strength testing requirements of each part of the installation shall be determined separately and tested accordingly. Figures 4(e) to 4(g) describe the strength testing requirements (of IGE/GM/8) either side of the pressure break for different situations.

4.3.3

For consistency with IGE/UP/1, IGE/UP/1A and IGE/UP/1B, the procedures incorporated in this Standard base STP on a multiple of MOP or MIP. This is based on the assumption that MOP will always equal DP, but this will not always be the case. When calculating STP, the following shall be applied:

 

if DP > MOP, the DP shall be used instead of MOP, and where available DMIP shall be used instead of MIP.



FIGURE 4 (a) - TYPICAL PRESSURE BREAK. FIRST OUTLET VALVE DOWNSTREAM OF THE PRESSURE REGULATOR (MIV FITTED)

FIGURE 4 (b) - TYPICAL PRESSURE BREAK. FIRST OUTLET VALVE DOWNSTREAM OF THE PRESSURE REGULATOR (NO MIV FITTED)

FIGURE 4 (c) - HIGHER REVERSE PRESSURE. PRESSURE BREAK ON THE INLET TO THE FIRST SAFETY DEVICE (NO MIV FITTED)

FIGURE 4 (d) - HIGHER REVERSE PRESSURE. PRESSURE BREAK ON THE INLET TO THE FIRST SAFETY DEVICE (MIV FITTED) 9 IGEM, IGEM House, High Street, Kegworth, Derbyshire, DE74 2DA. Website igem.org.uk.


FIGURE 4 (e) - DOWNSTREAM PRESSURE BREAK. NO ISSUES WITH COMPONENT STRENGTH (MIV FITTED)

FIGURE 4 (f) - DOWNSTREAM PRESSURE BREAK. REGULATOR DIAPHRAGMS NOT CAPABLE OF WITHSTANDING MOPU (MIV FITTED)

FIGURE 4 (g) - DOWNSTREAM PRESSURE BREAK, METER NOT CAPABLE OF WITHSTANDING MIPU, REGULATOR DIAPHRAGMS NOT CAPABLE OF WITHSTANDING MOPU (NO MIV FITTED) Note:

Some of the figures above are reproduced in Figure 6 with emphasise the tightness test requirements (shown in grey above).

FIGURE 4 - PRESSURE BREAKS. STRENGTH REQUIREMENTS



4.3.4

STP shall be determined using a multiple of either MIP or MOP (see Table 5) Normally, the values of MIP and MOP shall be obtained from the MAM. However, the majority of meter installations will have standard values as given in Tables 1 to 4. Before Regulator DMIPu DPu STPmiu

mbar 200 75 220

After Regulator MIPmi MOPmi STPmid

mbar 75 23 82.5

TABLE 1 - EXAMPLE 1. A LOW PRESSURE OUTLET FED FROM THE LOW PRESSURE NETWORK (NG). Before Regulator DMIPu DPu STPmiu

mbar 2700 2000 3000


mbar 50* 23 57.5*

* Figure depends on the set point of the slam shut valve.

TABLE 2 - EXAMPLE 2. A LOW PRESSURE OUTLET FED FROM THE MEDIUM PRESSURE NETWORK (NG). Before Regulator DMIPu DPu STPmiu

mbar 350 75 525


mbar 80 39 97.5

TABLE 3 - EXAMPLE 3. A LOW PRESSURE OUTLET FED FROM A LOW PRESSURE NETWORK (PROPANE) - BS 3016 REGULATORS Before Regulator DMIPu DPu STPmiu

mbar 2700 2000 3000


mbar 80 39 97.5

TABLE 4 - EXAMPLE 4. A LOW PRESSURE OUTLET FED FROM A MEDIUM PRESSURE NETWORK (PROPANE) - BS 3016 REGULATORS 4.3.5

Where a booster or compressor is included downstream of the installation being tested, the maximum back pressure (MIPc) shall be obtained from its owner. Where this pressure exceeds MIPmi, MIPc shall be taken as MIP.



4.4

METHOD, PRESSURE, DURATION AND TEST CRITERIA FOR STRENGTH TESTING The method, pressure (STP), duration (STD) and criteria for pneumatic strength testing shall be as given in Table 5. Where STP is calculated to exceed 3.5 bar for pipework of diameter exceeding 150 mm, or 10.5 bar for diameter exceeding 25 mm, a hydrostatic strength test shall be carried out in accordance with IGE/UP/1. Pneumatic testing shall not be carried out in such circumstances. MOP

Ø (mm)

 100 mbar

ALL

>100 2 >2 7

ALL

*

mbar bar bar bar

 150

STP (greater of)

1.1 2.5 1.1 1.5 1.1 1.5

MIP and MOP MIP and MOP MIP and MOP

STABILISE (mins)*

STD (mins)

MAXIMUM DROP % STP

5

5

20

10

5

20

15

30

20

Where surrounding conditions are stable, the responsible engineer may judge the installation to have stabilised before the time periods given.

TABLE 5 - SELECTION OF THE METHOD, PRESSURE, DURATION, AND THE TEST CRITERIA FOR STRENGTH TESTING 4.5

PROCEDURES

4.5.1

A thorough survey of the section to be tested, to detect any major integrity defect, shall be carried out before testing, including inspection of certificates, non-destructive testing (NDT), etc. As far as is reasonably practicable, joints should be exposed during the strength test to enable the use of LDF following a failed test.

4.5.2

It shall be ensured that all components are inspected prior to testing and have been designed, installed and anchored to withstand STP.

4.5.3

The following two situations will arise:



where all components within the section to be tested can withstand the highest STP, (as calculated from the two MOPs or MIPs), the highest STP should be used to test the whole section. Note:

Normally this will be the case with low pressure sourced metering installations.

or,



where certain components cannot withstand the highest STP of the assembly, the assembly shall be split so that two separate strength tests can be carried out, each at the appropriate STP.



4.5.4

Before testing, the following actions shall be taken:

 

ensure all isolation valves are plugged securely or blanked off and the valves are in the open position to ensure the valve body is tested where necessary, remove any component that is not to be included in the test. Remove any component or sub-assembly that could be damaged by STP prior to carrying out the strength test. Such a component or sub-assembly shall be, or be proved to have been, tested separately to an appropriate standard. Install spool pieces or blanks. Note 1: Components such as regulators, meters, non-return valves, safety shut-off valves etc, may need to be removed and replaced with spool pieces or sealed off with an appropriate fitting. Note 2: When a removed item(s) subsequently is(are) connected to the installation, it is not necessary to repeat the strength test for the whole installation before carrying out a tightness test, provided the connections are inspected carefully during the tightness test. Such connections, if welded, will need to have been subject to NDT to a standard equivalent to that used for the rest of the section.



ensure there is a means of pressurising the installation either with dry compressed air or nitrogen (above freezing point if expanded from bottled nitrogen)



incorporate (in the connection of the pressurisation medium to the installation) suitably adjusted regulators and a full flow safety valve(s) to prevent pressurisation above STP



4.5.5

if the assembly incorporates components that can trap pressure, for example a pressure regulator, it will be necessary to provide a pressure equalisation by-pass around such components. Any by-pass shall be suitable to withstand the pressure.

Appropriate instruments shall be provided to evaluate the test as follows, duplicated where necessary:

  

pressure recorders pressure gauges temperature recorders.

4.5.6

Gauges and recorders shall be certificated for calibration and, if appropriate, zeroed before use.

4.5.7

An exclusion zone, in accordance with Table 6, shall be set up around the area of any installation for which STP exceeds 1 bar. Personnel shall not be within this distance while pressurising or during the stabilization and test periods. Note:

In general, this will mean that the pressurisation equipment and test instruments are also outside this area, the latter being piped into the area in small bore pipework. The distances detailed in Table 5 are based on the centre-line of fittings and components and extend both sides.

For STP exceeding 7 bar, a suitable risk assessment shall be carried out to determine the distance required. STP (bar) >12 >25 >57

DISTANCE (m) 1 2 2.5

TABLE 6 - SAFETY DISTANCES EACH SIDE OF AN INSTALLATION FOR STRENGTH TESTING AT STP EXCEEDING 1 BAR



4.5.8

A final inspection of the section to be tested shall be carried out to ensure that it is ready for the test (it shall be ensured that any exclusion zone is clear of all personnel - see Table 6).

4.5.9

If STP exceeds 2 bar, a check for general integrity, for example for open ends, shall be carried out at a pressure of 350 mbar. The section shall be pressurised slowly. For STP exceeding 2 bar, after reaching 2 bar, the pressure shall be increased in 10% stages up to STP leaving a short period between each increase.

4.5.10

The pressure in the installation should be maintained at STP over the stabilization period.

4.5.11

At the end of the stabilization period, the pressure source shall be disconnected from the installation and the strength test duration (STD) (see Table 5) shall start. The gauge shall be monitored for the full test period.

4.5.12

If the installation fails the strength test (see Table 5 – permitted drop), the pressure shall be reduced to no greater than 1 bar prior to allowing personnel into the exclusion zone to test joints, glands, etc. for leakage, using LDF. Before work commences to remedy any leakage, the test pressure within the pipeline should be reduced to zero, by safely venting to atmosphere. Once any repairs are complete, a further strength test shall be carried out which shall be in accordance with the above procedures.

4.5.13

Following a satisfactory test (see Table 5 – permitted drop), the pressure in the installation should be reduced to OP if a tightness test is to be carried out immediately. If not, the pressure shall be vented and the installation left in a safe condition until the tightness test is to be carried out. Any exclusion zone then can be re-opened for all site personnel.

4.5.14

The strength test shall be documented and included in any site Health and Safety File. Results should be recorded on a formal certificate, a copy of which should be given to the MAM of the installation. STP and MOP shall be recorded clearly and be available for reference by any party subsequently working on the installation. Note:

IGEM publishes suitable triplicate certificates in pads.



START

GO TO TIGHTNESS TEST (5)

YES

FULLY PRE-TESTED, UNMODIFIED AND DOCUMENTED? (4.1.2 and 4.1.3)

YES

NEW INSTALLATION?

EXISTING. IS IT NECESSARY TO CARRY OUT A STRENGTH TEST? (4.1)

NO

YES

NO SELECT METHOD, STP AND STD (TABLE 5)

REMOVE AND REPLACE/SEAL

GO TO TIGHTNESS TEST (5)

NO

YES

YES

IS IT SAFE TO STRENGTH TEST? (4.5.1 and 4.5.2)

RE-ASSESS CONSTRUCTION AND TEST METHOD. ELIMINATE UNACCEPTABLE RISK OR ELIMINATE NEED TO STRENGTH TEST. RETURN TO “START”.

NO

DO COMPONENTS OR SUB ASSEMBLIES NEED TO BE REMOVED? (4.5.3) NO APPLY PRECAUTIONS AND TEST (4.5)

TEST PASS? (TABLE 5)

NO

DE-PRESSURISE AND REPAIR

YES DOCUMENT AND GO TO TIGHTNESS TEST (5)

Note:

This algorithm does not show all necessary steps and the full procedures in Section 4 apply.

FIGURE 5 - FLOW-CHART/DECISION TESTING

ALGORITHM

FOR

STRENGTH



SECTION 5 : TIGHTNESS TESTING Even if a tightness test result is satisfactory, any smell of gas or a gas detector reading indicating the presence of gas is not acceptable. However, for an existing installation, the test may be against isolation valves which could be relatively old and worn, so a defined maximum level of leakage is permitted. Some LDFs have an adverse effect on certain installation materials. Consequently, any residual fluid shall be washed off thoroughly and subsequently be dried. LDFs containing more than 30 parts per million of halogens shall not be used on stainless steel components. If necessary, for example when joints are broken, temporary continuity bonds shall be installed before testing. 5.1

DECISION WHETHER TO TIGHTNESS TEST Tightness testing is required under the following circumstances:

   

prior to a new installation being commissioned with gas, where a leak is suspected to exist on an existing installation, where a new section has been added into an existing installation, where there has been a complete loss of pressure, for any reason, for example component replacement, section replacement, etc.

When repairing/modifying/replacing components on an existing installation which has resulted in a loss of pressure due to opening the gasways, it is only necessary to undertake a tightness test on the section that has lost pressure. As such, particularly on larger installations, as much of the meter installation as possible should be kept pressurised, along with the consumers system, (see Figure 3). Where the downstream installation pipework is being kept live the pressure should be maintained at OP. It should be ensured that there are no major leaks on the temporary pipework supplying the gas, by using LDF or a gas detector, as appropriate. 5.2

GENERAL

5.2.1

A thorough survey of the section to be tested shall be carried out before testing, to detect and correct any major integrity defect.

5.2.2

For any installation of tightness test pressure (TTP) exceeding 1 bar, either the safety distances given in Table 6 shall be applied or the test carried out when the premises are unoccupied.

5.2.3

If an installation contains fuel gas, it should be tested with fuel gas unless a complete purge to air is carried out (see Section 6) before testing with air.

5.2.4

Where an installation containing air is pressurised with fuel gas, and following a satisfactory tightness test, it shall immediately be purged to fuel gas. If the tightness test should fail, the leak shall be traced and repaired. If it is necessary to open the gasways to do this, the installation shall be depressurised and purged to air (see Section 6).



5.3

DETERMINATION OF TTP The tightness test is normally undertaken with a TTP of OP. The majority of meter installations incorporate a pressure regulator, and as such will normally incorporate a pressure break, and have sections operating at different OPs, which result in different TTP requirements. The section downstream of the pressure break shall be tested with a TTP ≥ OPmi. Any section on the inlet side of the pressure regulator(s) that can be tested as a separate section at OPu, shall be tested with a TTP equal to OPu. The section incorporating the pressure regulators and safety devices is more problematic. The pressure regulators will have to be by-passed and the whole section tested at either OPu or OPmi:

 

where all components within the section to be tested can withstand OPu, the whole section should be tested at OPu. where components may be damaged by pressurising the downstream side of the pressure regulators to OPu, the whole section shall be tested with a TTP equal to OPmi, and all the joints upstream of the pressure regulators subsequently tested with LDF at OPu.

FIGURE 6 (a) - DOWNSTREAM PRESSURE BREAK, NO ISSUES WITH COMPONENT STRENGTH (MIV FITTED)

FIGURE 6 (b) - DOWNSTREAM PRESSURE BREAK REGULATOR DIAPHRAGMS NOT CAPABLE OF WITHSTANDING MOPU (MIV FITTED)



FIGURE 6 (c) - DOWNSTREAM PRESSURE BREAK, METER NOT CAPABLE OF WITHSTANDING MIPU, REGULATOR DIAPHRAGMS NOT CAPABLE OF WITHSTANDING MOPU (NO MIV FITTED) FIGURE 6 - PRESSURE BREAKS. TIGHTNESS TEST REQUIREMENTS 5.4

TIGHTNESS TEST DURATION (TTD)

5.4.1

The TTD shall be either:

 

as specified in Tables 7, 8 or 9 as appropriate or, for those installations and gauges not covered by Tables 7, 8 or 9 the TTD shall be calculated in accordance with Appendix 4. DESIGNATION OF METER G4/U6 G10/U16 G16/U25 U40 G40/U65 G65/U100 U160 RD or turbine up to 100mm NB and up to 5 m length

NG 2 2 2 3 4 7 11 2

TTD (mins) PROPANE 2 4 5 9 13 23 See Note 2 5

Note 1: If adopting the concept of NPM, TTD can be calculated by dividing the durations given above by 2 and rounding up to the nearest minute, with a minimum test time of 2 minutes. Note 2: TTD would be above 30 mins, and IGE/UP/1 needs to be consulted. Note 3: Further TTDs for larger installations are shown in Tables 8 and 9.

TABLE 7 - TIGHTNESS TEST DURATION (MINS) FOR TYPICAL INSTALLATIONS AND USING A PRESSURE GAUGE WITH A GRM OF 0.5 MBAR



5.5

PROCEDURES - TIGHTNESS TESTING

5.5.1

By-passing components

5.5.1.1

If there is any component in the section to be tested that could trap pressure, for example a regulator, a non-return valve (NRV), etc., the component concerned shall be by-passed temporarily to equalize the pressure either side of the component. All valves shall be open, or by-passed.

5.5.1.2

When constructing a by-pass, particular care shall be taken to use materials/components and security (via anchorage, etc.) suitable for the test pressure (IGEM/UP/2 provides requirements). Care shall be taken to avoid damage to regulator diaphragms, filters, etc.

5.5.2

Ambient conditions

5.5.2.1

Where a section to be tested includes exposed pipework, the test shall be carried out taking account of ambient conditions i.e. when ambient conditions are stable. Testing shall not be carried out if any part of the installation would be exposed to direct sunlight during the test period.

5.5.2.2

For an installation in a building, testing should take place when the temperature will not change over the test period.

5.5.3

Section and valve isolation

5.5.3.1

Testing with nitrogen/air All valves in the section to be tested shall be spaded off, plugged or capped and left in the open position, in order that the test will include the valves and will be made against sealed ends. The ECV shall be spaded off on the downstream side.

5.5.3.2

Testing with fuel gas A let-by test shall be carried out on the section inlet and outlet valves.

5.5.4

Testing

5.5.4.1

The following tightness test procedure shall be followed: (a)

If testing an installation with fuel gas, a let-by test of the installation isolation valve(s) shall be carried out, ensuring the valve(s) is/are closed, by adjusting the pressure to approximately 50% OP. If, over the same test period as calculated for the tightness test (TTD), a rise in pressure of more than GRM is observed, the isolation valve may be letting-by. Any defective isolation valve shall be repaired/replaced before proceeding to the tightness test. If let-by is confirmed on an ECV, the Gas Emergency Contact Centre (for Propane, the gas supplier) shall be notified and the installation made safe, suspending the test until a repair has been made.

(b)

If TTP exceeds 2 bar, a check for general integrity, for example for open ends, shall be carried out at a pressure of 350 mbar. The section shall be pressurised slowly. For TTP exceeding 2 bar, after reaching 2 bar, the pressure shall be increased in 10% stages up to TTP leaving a short period between each increase.



(c)

The temperature should be allowed to stabilise for TTD or for 15 mins, whichever is the longer. The source of pressure shall then be isolated.

(d)

The gauge shall be monitored as necessary for the duration of the test. Any movement of the gauge shall be less than GRM (Table 16). If greater movement is detected, the test has failed and the leak(s) shall be located and rectified and the test repeated. Note:

(e)

For the scope of this Standard, correction for atmospheric pressure and temperature variations is not needed.

If spades, etc. are fitted, the installation shall be de-pressurised, the spades, etc. removed and any disturbed joints checked with LDF.

5.6

COMPLETION

5.6.1

If testing on air the pressure shall be released in a safe and controlled manner, and the section may be purged to fuel gas immediately following a successful tightness test. If purging is not carried out immediately, a further tightness check must be carried out immediately prior to purging.

5.6.2

Where a section containing air has been tested with fuel gas, following completion of a satisfactory tightness test, the section shall be immediately purged to fuel gas. If the test should fail, the leak shall be traced and repaired. If it is necessary to open the gas ways, the section shall be de-pressurised and purged to air prior to undertaking repairs.

5.6.3

After proving tightness, any purging shall be carried out as detailed in Section 6.

5.6.4

The tightness test shall be documented and included in any site Health and Safety File. Results should be recorded on a formal certificate, a copy of which should be given to the MAM of the pipework tested. OP shall be recorded clearly and be available for reference by any party subsequently working on the installation. Note:




START

YES STRENGTH TEST CARRIED OUT OR PRE-TESTED AND/ OR ALL EXISTING EQUIPMENT CERTIFICATED?

NO

STRENGTH TEST, PASS?

NO

DO NOT TIGHTNESS TEST, RECONSTRUCT

YES

FIT TEMPORARY BY-PASSESS FOR COMPONENTS THAT WILL TRAP GAS

FIT SPADES/PLUGS TO ALL VALVES AND TEST IN OPEN POSITION

IS THE SITE SURVEY SATISFACTORY?

NO

COMPLETE REMEDIAL WORK

YES

SELECT TTD (5.4) OR CALCULATE TTD (APPENDIX 4)

ADJUST PRESSURE TO TTP

ALLOW TO STABILISE

TRACE LEAK, REPAIR AND RE-TEST

REPAIR AND RE-TEST

YES CARRY OUT TIGHTNESS TEST, TOTALLY GAS TIGHT? YES

NO

GAUGE READING DROP LESS NO THAN PERMITTED DROP AND NO SMELL OF GAS?

CAN LEAK BE TRACED AND REPAIRED WITHOUT DE-COMMISSIONING?

NO

DE-PRESSURISE

YES

COMPLETE DOCUMENTATION (5.6) AND PURGE (SECTION 6)

Note:


FIGURE 7 - FLOW CHART/DECISION ALGORITHM TESTING WITH AIR OR NITROGEN

FOR

TIGHTNESS



START

YES STRENGTH TEST CARRIED OUT OR PRE-TESTED AND/ OR ALL EXISTING EQUIPMENT CERTIFICATED?

NO

STRENGTH TEST, PASS?

NO

DO NOT TIGHTNESS TEST, RECONSTRUCT

YES

FIT TEMPORARY BY-PASSESS FOR COMPONENTS THAT WILL TRAP GAS

FIT SPADES/PLUGS TO ALL VALVES AND TEST IN OPEN POSITION, EXCEPT SECTION ISOLATION VALVES

IS THE SITE SURVEY SATISFACTORY?

NO

COMPLETE REMEDIAL WORK

YES

SELECT TTD (5.4) OR CALCULATE TTD (APPENDIX 4)

CARRY OUT LET-BY TEST ON NO SECTION ISOLATION VALVE(S), SATISFACTORY?

REPAIR VALVE OR ISOLATE SECTION BY OTHER MEANS (5.5.4.1 (a))

YES

ADJUST PRESSURE TO TTP

ALLOW TO STABILISE

TRACE LEAK, REPAIR AND RE-TEST

REPAIR AND RE-TEST

YES CARRY OUT TIGHTNESS TEST, TOTALLY GAS TIGHT? YES

NO

GAUGE READING DROP LESS NO THAN PERMITTED DROP AND NO SMELL OF GAS?

CAN LEAK BE TRACED AND REPAIRED WITHOUT DE-COMMISSIONING?

NO

DE-PRESSURISE AND PURGE TO AIR OR NITROGEN

YES

COMPLETE DOCUMENTATION (5.6) AND PURGE (SECTION 6)

Note:


FIGURE 8 - FLOW CHART/DECISION ALGORITHM FOR TIGHTNESS TESTING WITH FUEL GAS



LENGTH (m) DIAMETER (mm)

Note:

1

2

3

4

5

6

7

8

9

10

40

2

2

2

2

2

2

2

2

2

2

50

2

2

2

2

2

2

2

2

2

2

80

2

2

2

2

2

2

2

2

2

2

100

2

2

2

2

2

3

3

3

3

4

150

2

2

3

3

4

5

5

6

7

7

200

2

3

4

5

6

8

9

10

11

12

250

2

4

6

8

9

11

13

15

16

18

300

3

5

8

10

13

15

18

20

23

25

If adopting the concept of NPM, TTD can be calculated by dividing the durations given above by 2 and rounding up to the nearest minute, with a minimum test time of 2 minutes.

TABLE 8 - TIGHTNESS TEST DURATIONS (MINS) FOR RD AND TURBINE METERS USING A GAUGE WITH A GRM OF 0.5 MBAR (NATURAL GAS)

LENGTH (m) DIAMETER (mm)

1

2

3

4

5

6

7

8

9

10

40

2

2

2

2

2

2

2

2

2

2

50

2

2

2

2

2

2

2

3

3

3

80

2

2

2

3

3

4

5

5

6

6

100

2

2

3

4

5

6

7

8

9

10

150

3

5

7

9

12

14

16

18

20

23

200

4

8

12

16

20

24

28

Note 2

Note 2

Note 2

250

6

12

18

24

30

Note 2

Note 2

Note 2

Note 2

Note 2

300

9

17

25

Note 2

Note 2

Note 2

Note 2

Note 2

Note 2

Note 2

Note 1: If adopting the concept of NPM, TTD can be calculated by dividing the durations given above by 2 and rounding up to the nearest minute, with a minimum test time of 2 minutes. Note 2: TTD would be above 30 mins, and IGE/UP/1 needs to be consulted.

TABLE 9 - TIGHTNESS TEST DURATIONS (MINS) FOR RD AND TURBINE METERS USING A GAUGE WITH A GRM OF 0.5 MBAR (PROPANE) 23 IGEM, IGEM House, High Street, Kegworth, Derbyshire, DE74 2DA. Website igem.org.uk.


SECTION 6 : DIRECT PURGING This section deals with direct purging with air or fuel gas. If, for any reason, the purge is not complete, it will be necessary to carry out an indirect purge using nitrogen (N2), guidance on which is provided in Appendix 3 (see also clause 6.1.2 and Sub-Section 6.8). This Standard assumes that the installation will be pressurised during purging. 6.1

GENERAL

6.1.1

The environmental impact of releasing methane into the atmosphere shall be considered and the volume of any vented gas should be minimised, for example by minimising the section to be purged through the use of appropriate isolation valves, only purging the section being worked on and not significantly exceeding the calculated purge volume.

6.1.2

For propane, reference should be made to the advice contained in Appendix 5 when assessing safety. If the assessment indicates that safety would be compromised, the heavier-than-air gas shall be purged indirectly seeking specialist advice if necessary. Heavier-than-air gases shall be flared.

6.1.3

A tightness test must be carried out immediately prior to any purge admitting gas. Vent points shall be leakage tested. Note:

This equally applies when admitting N2 to be followed by NG/Propane (see Appendix 3).

6.1.4

The pressure created during purging shall not exceed MOP of any component being purged.

6.1.5

If compressed air/nitrogen from a cylinder is used for purging, the air shall be supplied through high capacity regulators, appropriate precautions being taken for example pressure gauges, safety devices and multi stage regulation. Note:

6.1.6

This is to prevent icing of regulators and excess pressure being applied.

Where an installation is to be taken permanently out of use, it shall be isolated physically, for example by spading or removing a component and sealing the ends. Any de-commissioned installation shall be left purged to air.

6.1.7

Where an installation is to be taken temporarily out of service for repairs or alterations, a let-by test shall be carried out on any valve(s) to be used to isolate the installation (see clause 5.5.4.1(a)). Where an installation is left unattended, it shall be isolated physically, for example by spading or, where not practicable, by reliably locking off to prevent unauthorised operation.

6.2

PLANNING AND SUPERVISION

6.2.1

The meter installation shall be checked to ensure that it has all necessary valves and sufficient access points to allow the purging operation to take place safely.

6.2.2

Purging of a meter shall be carried out only with the agreement of its owner prior to the purge.



6.2.3

Purging shall be planned carefully and the following procedures shall be undertaken as appropriate:

 

determine the required number of gas operatives



for complex purging operations, prepare a written procedure for the operation. If it is anticipated that cutting or welding of any part of the installation may take place after completion of purging, consideration shall be given to the use of a “permit to work” system.

survey the installation to establish that it is in a satisfactory condition. Any defect shall be corrected before any purging is undertaken, unless decommissioning

6.2.4

During the purging operation, all other work on the installation being purged shall be prohibited.

6.2.5

The complete purge procedure shall be continuous and the minimum purge flow rate, and hence the minimum velocity, given in Table 10 shall be achieved. Note 1: This is to prevent stratification and, hence, low or zero flow of one of the contained gases. Note 2: It is not a requirement to purge at OP. In general, if purge points are sized adequately, the minimum required velocity will be achieved more easily at lower pressures (see Table 10, column 5).

If it becomes immediately apparent that a direct purge will not achieve the required flow rate, the restriction may be removed and the purge re-started. Otherwise, an indirect purge using N2 shall be carried out (see Appendix 3). Consequently, planning shall take into account the need for sufficient quantities of N2 to be available. 6.2.6

Purge points shall be located at the remote ends of the section to be tested.

6.2.7

Purge points shall be located as close as possible to the extremities of the installation to enable a complete purge.

6.2.8

When purging with air, it must be ensured that air will not enter the GT’s or any other distribution network.

6.3

SITE PRECAUTIONS

6.3.1

Warning notices and labels

6.3.1.1

Appropriate “No smoking” and/or “No naked lights” signage shall be displayed prominently around any vent and the overall area where purging will take place.

6.3.1.2

Any valve to or from the installation to be purged shall be labelled clearly, for example “Do not operate – purging in progress”.

6.3.2

Electrical and fire

6.3.2.1

Where appropriate, due regard shall be paid to the intrinsic safety of any electrical equipment used in the vicinity of the vent points.

6.3.2.2

Any fitted electrical continuity bonds shall be maintained throughout the purging operation.

6.3.2.3

Sufficient and appropriate fire extinguishers should be situated near the vent point(s).



6.4

DESIGNING AND POSITIONING PURGE POINTS, HOSES AND VENT STACKS

6.4.1

Precautions shall be taken to reduce, as far as possible, the hazards associated with venting, for example by avoiding venting close to property air intakes, or to any potential sources of ignition such as street lamps and electrical plant. If there is any doubt about the minimum clearance to ignition sources, reference should be made to IGE/SR/23. Any electrical switch or isolator in the vicinity of the vent outlet shall not be operated during purging. Consideration shall be given to potential complaints of smell arising from any purging operation and prior notice should be given to any persons identified as liable to notice purged gas by smell.

6.4.2

Purge points, associated vents, hoses and vent stacks shall be sized to permit sufficient flow in order to maintain the required purge rate/velocity, Table 10, columns 4 and 5 should be used. Note:

Where the minimum required size of purge hose and vent stack cannot be achieved, multiple vents may be used. These may be operated simultaneously, provided each point is supervised and communications are adequate to enable a safe purge.

Any valve used in the purge process should be full bore, where possible. 6.4.3

Any vent stack should terminate with a suitable flame arrestor. Note:

Where the purge velocity can be guaranteed, it may not be necessary to fit an arrestor but suitable additional precautions are required.

6.4.4

Any vent stack shall incorporate a full bore control valve and sample point.

6.4.6

The purge hose shall be:

  

suitable for containing the fuel gas gas tight secured firmly to the purge point Note:



Unsecured push-on connections are not acceptable.

earthed suitably to avoid sparking, if necessary, for example for externally armoured hose.

Hose materials that may generate static electricity, for example PE, shall not be used. Note:

The possibility of generating static electricity increases as the purge velocity increases.

6.4.7

Any vent outlet should be located in open air, terminate at least 2.5 m above ground and be located at least 5 m downwind of any potential ignition source.

6.4.8

Precautions shall be taken to prevent vented gas drifting into buildings.

6.4.9

When purging small volumes, purging may be carried out directly into a well ventilated internal area without the use of a purge hose, vent stack or flame arrestor, but only if all the following criteria are satisfied:

  

OP of the section being purged shall not exceed 21 mbar the total volume of the pipework to be purged shall not exceed 0.02 m3 with the exception of an external purpose built meter house, the volume of the internal area shall not be less than 30 m3 Note:

The exception for purpose built meter houses is only applicable where there is no means of gas entering the building from the housing.





the internal area shall be well ventilated, for example with windows and doors open and any mechanical ventilation in operation



the purge point(s) shall be located in a well ventilated section of the internal area and shall not exceed 25 mm

 

there shall be no potential ignition sources within 3 m of any purge point



the valve used to control the purge shall be in the same internal area as the purge point(s) the gas concentration in the area shall be monitored and, as far as is possible, it shall not be permitted to exceed 10% lower flammability limit (LFL). If it does, the purge shall be stopped immediately and the system purged to outside.

6.5

VERIFICATION OF PURGE VELOCITY

6.5.1

A method of verifying that the required purge velocity (Table 10) is achievable shall be available and shall be one of the following:

 

a suitably sized “volume” meter (used in conjunction with a timer to enable the flow rate to be calculated) already fitted in the section of pipework to be purged a suitably sized “rate of flow” meter, i.e. capable of passing well in excess of the purge flow rate or other suitable flow measuring device fitted downstream of the purge point(s), such as an independent positive displacement or turbine meter.

Note 1: Usually, the meter being purged will fulfil this function. However, for short purge times, the purge gas passed may not register. Note 2: Provided there is confidence (see also clause 6.2.5) that the required purge velocity (Table 10) will be achieved, a timed passage of purge gas (see clause 6.9.4) may be used at the discretion of a responsible, competent person.

6.5.2

A test of the vent gas shall always be carried out (see Sub-Section 6.10).

6.6

IDENTIFICATION OF PURGE GAS CYLINDERS When the purge gas for example, air/nitrogen is supplied from a cylinder, special care shall be taken to ensure that the cylinder does not contain the wrong gas, for example oxygen. Cylinders shall be checked in this respect, before use. Note:

6.7

This can be achieved, for example by using an oxygen detector or by confirmation of the contents of the cylinder by the supplier, etc.

GAS DETECTORS, OXYGEN ELECTRONIC EQUIPMENT

MEASURING

DEVICES

AND

OTHER

Any gas detector, oxygen measuring device or other electronic equipment shall:

 

comply with Sub-Section 3.4

 

have its batteries tested prior to use



be tested, overhauled and calibrated in accordance with the manufacturer’s instructions.

be operated in accordance with the manufacturer’s instructions and by a trained competent person capable of interpreting the results obtained be zeroed at the commencement of each test and have its zero checked at the finish of each test



6.8

DETERMINATION OF THE PURGE VOLUME, MINIMUM PURGE FLOW RATE AND PURGE TIME

6.8.1

The purge volume (PV) of the installation and purge hose/vent pipe shall be calculated as follows: Note:



The volume of the purge hose may be significant in relation to small volumes of installation and this needs to be taken into consideration.

PV of a diaphragm meter = 5 x cyclic volume (Table 14) Note:

The cyclic volume (capacity per revolution) is shown either on the index plate of modern meters or, on older tin case meters, on the badge plate.



PV of a RD, turbine or ultrasonic meter = 1.5 x volume of an equivalent length of pipe (see Table 14)



PV of the remainder of pipework and components within the installation = 1.5 x (IVp + IVf) (see Appendix 4)



PV of a purge hose/vent pipe = 1.5 x volume of hose/pipe (Table 14).

The total purge volume (PV) is the sum of the above. 6.8.2

It should be confirmed that the velocity of the purging medium through the pipe is above a minimum level, to ensure that the effect of stratification does not impair the purging. Note:

6.8.3

The minimum purge flowrate (Q) shall be determined from Table 10. For an installation including significant volumes of pipe, the largest diameter pipe shall be used to determine Q. Note:

6.8.4

Although velocity is not easily measured in such a situation, it can be related to purge flow rate which can be monitored with a flow meter or a timing method.

If Q is not achieved, the purge time and volume of purge gas required will be excessive and, even then, a satisfactory purge may not be achieved as the minimum velocity required, the key factor, will also not be achieved.

Where necessary (see clause 6.5.1), the maximum purge time (PTmax) shall be calculated as follows: PTmax (secs) = Note:

PV(m3 ) x 3600 Q (m3 h1)

This is the maximum time (purge time) it will take before a vent gas test should indicate a sufficient quantity of fuel gas or air as appropriate to indicate completion of the purge.

Example: A single filter and regulator within a section of 80 mm pipe of total length 0.8 m. An RD meter with no by-pass, fitted in a section of 100 mm pipe of total length 1.2 m. 6 m long purge hose of 40 mm diameter. PV PV PV

= = =

(1.5 X 0.8 X 0.0054) + (1.5 X 1.2 X 0.009) + (1.5 X 10 X 0.0015) (0.00648) + (0.0162) + (0.0225) 0.0452 m3

Minimum purge flow rate from Table 10 for 100 mm pipe is 0.33 m3/min PTmax is therefore 0.0452/0.33 – 0.137 mins = 9 secs.


IGEM/UP/1C – Draft for Comment (2nd Consultation) 2

3

4

5

NOMINAL PIPE DIAMETER TO BE PURGED

1

MINIMUM PURGE VELOCITY

MINIMUM PURGE FLOW-RATE (Q)

PURGE HOSE/ VENT STACK NOMINAL BORE

FLAME ARRESTER NOMINAL BORE

mm

m s-1

mm

mm

20 25 32 40 50 80 100 125 150 200 250 300 400

m3 min-1

m3 h-1

0.01 0.02 0.03 0.05 0.08 0.19 0.33 0.5 0.7 1.32 2.35 3.6 7.9

0.7 1.0 1.7 2.5 4.5 11 20 30 38 79 141 216 473

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.7 0.8 0.9 1.0

20 20 20 20 40 40 40 50 50 100 100 150 150

20 20 20 20 50 50 50 50 50 200 200 200 200

TABLE 10 - MINIMUM PURGE FLOW RATE AND VELOCITY WITH RECOMMENDED MINIMUM PURGE POINT, ASSOCIATED VENT AND FLARE STACK DIMENSIONS 6.9

VENT GAS TESTING The criteria given in Table 11 shall be used when testing the vent gas. Note:

FUEL TYPE (GAS OR VAPOUR)

Table 8 is intended to ensure safe conditions, but not necessarily efficient combustion performance.

SPECIFIC GRAVITY: AIR = 1 (See Note 1)

NATURAL GAS PROPANE

0.6 1.5

FLAMMABILITY LIMITS LOWER UPPER LIMIT % LIMIT % GAS IN GAS IN AIR AIR 4.5 15.5 2.1 10.1

SAFE PURGE END POINTS DIRECT PURGE FROM AIR TO GAS

DIRECT PURGE FROM GAS TO AIR (see Note 4)

90% fuel gas See Note 2

1.8% gas See Note 2

Note 1: Specific gravity of gases in relation to air, <1 being lighter-than-air and >1 being heavierthan-air. Note 2: It is recommended that these gases be purged using N2 rather than air due to their low LFLs or high specific gravity. Refer to Appendix 3 for N2 purging. Note3:

Gas detectors used for differing gases need to be calibrated for the particular gas being tested. For NG, most instruments are calibrated for methane which, normally, forms well over 90% of NG.

Note 4: This end point is at 40% LFL.

TABLE 11 - FLAMMABILITY LIMITS AND SAFE PURGE END POINTS 6.10

PURGING PROCEDURES

6.10.1

Direct purging from air to gas i.e. commissioning The procedure assumes that, prior to purging, any purge point and any valve on any connected vent stack is closed, that the installation isolation valve(s) is/are closed and that any other valve within the installation is open.



Throughout the purge operation, steps should be taken to ensure that any upstream pipework or appliance will not be affected by the purging operation. Note:

On larger installations at higher pressures, for example exceeding 2 bar, it may be necessary to use a valved rider to bypass the installation isolation valve, in order to enable a satisfactory level of control of pressurisation. It also may be necessary to introduce a pressure regulator into the rider to control the supply pressure to prevent overpressurisation of attached purge hoses and vents.

The following procedure shall be carried out: (a)

Ensure that a satisfactory tightness test (Section 5) has been carried out, immediately before starting the purge.

(b)

Open all purge points and open valves on connected vent stacks and the installation isolation valve to admit gas. Simultaneously, start the chosen method of measuring the flow of purge gas (see clause 6.5.1), i.e.;

 

start a timer and read the in-line meter or read the flow meter rate.

Note:

(c)

After half the estimated purge time (see clause 6.9.3) has elapsed (or earlier if desired – which may limit the wastage of gas), start testing the concentration of fuel gas in the vent gas using a suitable gas detector. Note:

(d)

If using a flow meter, it will be immediately apparent if the minimum required purge volume rate is not being achieved. In this case, it may be possible to stop the purge, rectify the reason for the incomplete purge and re-start the purge (from the beginning) without resorting to an indirect (N2) purge (see (d) below).

For an RD meter, the purge time could be very short and it may not be practical to start testing so early in the purge.

Stop the purge by closing the vent stack valve(s) (and record the in-line meter reading, if applicable) when a level of fuel gas, as indicated in Table 11 for safe purge end point, is achieved, or the metered purge volume has passed. Note:

Any method has to be verified by a satisfactory vent gas sample.

If Table 11 concentrations are not achieved within the purge time (or by the time the purge volume has passed) an incomplete purge is indicated. In this case, close the installation isolation valve(s) and immediately purge the section with N2 in accordance with Appendix 3. Before repeating steps (a) to (d), identify and rectify the reason for the incomplete purge. Note 1: For any "partially complete" purge, the pipework will contain a mixture of gas and air that is potentially hazardous. If it is possible to rectify the problem without opening the gasway, then it may be acceptable to so rectify and re-start the purge from the beginning. In the intervening period, it is imperative that the gasway is not opened, that any installation isolation valve is not opened, that the installation is not left unattended and that site precautions (see Sub-Section 6.3) remain in place. An overall risk assessment is required which, if sufficient assurance of safety is not indicated, will lead to an indirect purge using N2 (see Appendix 3). Note 2: The reason for an incomplete purge is likely to be insufficient velocity of the NG. Check the purge time recorded against any meter reading/ flow rate recorded. Any metered reading less than PV is suspect (see clause 6.9.1). Any flow rate less than PV expressed as a flow rate is also suspect (see clause 6.9.2). If both are satisfactory, re-check the calculations (see Sub-Section 6.9). If no problem is found, it is likely that the actual design of the section is not as assumed when calculating PV. Note 3: In conjunction with a stopwatch for metered flow, all the above methods will serve to confirm that the purge velocity is the minimum required (see Table 7).



(e)

Close all purge points, disconnect vent stacks, remove all purge equipment and plug or cap the open ends with an appropriate fitting. Test any disturbed joints with LDF or a gas detector. Note 1: A gas detector is not permitted to move from zero or 0% LFL on the 0% to 10% LFL scale. Note 2: Disconnected purge equipment (hoses, meters, etc.) will need to be purged of NG.

(f)

Rectify the cause of any detected escapes or smell of gas.

(g)

Seal with an appropriate fitting the outlet of the installation and label to indicate that gas is turned on and purged up to that point.

(h)

Complete an appropriate purging certificate. Note:

6.10.2


Direct purging from gas to air i.e. de-commissioning The following procedure assumes that, prior to purging, any purge point and any valve on any connected vent stack is closed, that the installation isolation valve is closed and that any other valve within the installation is open. Any appliance attached to the section shall be turned off. Throughout the purge operation, steps should be taken to ensure that any upstream pipework or appliance will not be affected by the purging operation. The following procedure shall be carried out: (a)

Carry out a let-by test on the installation isolation valve(s), to prove its/their integrity (see clause 5.5.4.1 (a)).

(b)

Ensure the installation isolation valve(s) is/are turned off.

(c)

Ensure OP of the section will not be exceeded. Note:

(d)

Open all purge points and valves on connected vent stacks and admit air. Simultaneously, start the chosen method of “measuring” the flow of air (see clause 6.5.1) i.e.  start a timer and  read the in-line meter, or read the flow meter rate. Note:

(e)

If using a flow meter, it will be immediately apparent if the minimum required purge volume rate is not being achieved. In this case, it may be possible to stop the purge, rectify the reason for the incomplete purge and re-start the purge (from the beginning) without resorting to an indirect (N2) purge (see (f) below).

After half the estimated purge time (see clause 6.9.3) has elapsed (or earlier if desired) start testing the concentration of air in the vent gas using an appropriate instrument. Note:

(f)

This will require a suitable pressure gauge to be fitted as close as practicable to the air inlet point. Limiting the pressure can, normally, be achieved with the use of a low-pressure air blower(s) or, in the case of refillable cylinder(s)/tank(s), with the use of a suitable regulator that can be accurately set to a pressure at or below OP. Low-pressure air blower(s), cylinder(s)/tank(s), and regulator(s) need to be sized to pass the required purge flow rate.

For an RD meter, the purge time could be very short and it may not be practical to start testing so early in the purge.

Stop the purge by isolating the air supply (and record the in-line meter reading, if applicable) when a level of air, as indicated in Table 11 for



safe purge end point, is achieved or the metered purge volume has passed, whichever occurs first. Note:

Any method has to be verified by a satisfactory vent gas sample.

If Table 11 concentrations are not achieved within the purge time (or by the time the purge volume has passed) an incomplete purge is indicated. In this case, close the installation isolation valve(s) and immediately purge the section with N2 in accordance with Appendix 3. Before repeating steps (a) to (d), identify and rectify the reason for the incomplete purge. Note 1: For any "partially complete" purge, the installation will contain a mixture of fuel gas and air that is potentially hazardous. If it is possible to rectify the problem without opening the gasway, then it may be acceptable to so rectify and re-start the purge from the beginning. In the intervening period, it is imperative that the gasway is not opened, that any installation isolation valve is not opened, that the installation is not left unattended and that site precautions (see Sub-Section 6.3) remain in place. An overall risk assessment is required which, if sufficient assurance of safety is not indicated, will lead to an indirect purge using N2 (see Appendix 3). Note 2: The reason for an incomplete purge is likely to be insufficient velocity of NG. Check the purge time recorded against any meter reading/ flow rate recorded. Any metered reading less than PV is suspect (see clause 6.9.1). Any flow rate less than PV expressed as a flow rate is also suspect (see clause 6.9.2). If both are satisfactory, re-check the calculations (see Sub-Section 6.9). If no problem is found, it is likely that the actual design of the installation is not as assumed when calculating PV. Note 3: Provided there is confidence (see also clause 6.2.5) that the required purge velocity (Table 10) will be achieved, a timed passage of purge gas (see clause 6.9.4) may be used at the discretion of a responsible, competent person.

(g)

Close all purge points, disconnect vent stacks, remove all purge equipment and plug or cap the open ends with an appropriate fitting. Test any disturbed joints with LDF. Seal or disconnect pipework from the gas supply, sealing all ends with an appropriate fitting. Note:

Disconnected purge equipment (hoses, meters, etc.) will need to be purged of NG.

(h)

Label all pipework to show that it has been de-commissioned.

(i)

Complete an appropriate purging certificate. Note:




AIR TO GAS Commissioning Ensure that a satisfactory tightness test has been carried out Carry out all preparation work (6.2, 6.3, 6.4, 6.6, 6.7)

Vent stacks and hoses correctly located. Notices, barriers, fire extinguishers available and checked. Test meters and gas detectors checked.

Calculate:  purge volume  purge flow rate  purge time (6.9) Isolate potential ignition sources and erect warning signs (6.3)

Open vent point valve(s)

Immediately admit fuel gas at correct flow rate (6.11.1 (b))

Monitor gas pressure

Monitor gas flow rate

If correct flow rate cannot be achieved, abandon purge and use indirect method (Appendix 3)

Sample at vent point after purge time

After satisfactory vent gas test, close vent point valve and remove purge hose from vent

Check purge is complete (Table 11)

Test all disturbed joints and joints in ducts for leaks. Seal all outlets

Complete records and inform responsible person of position

FIGURE 9 - FLOWCHART FOR DIRECT PURGING OF AIR TO GAS



GAS TO AIR De-commissioning Carry out all preparation work (6.2, 6.3, 6.4, 6.6, 6.7)

Calculate:  purge volume  purge flow rate  purge time (6.9)

Vent stacks and hoses correctly located. Purge gas (air) supply available. Notices, barriers, fire extinguishers available and checked. Test meters and detectors checked.

Isolate potential ignition sources and erect warning signs (6.3)

Open vent point valve(s)

Immediately admit air at correct flow rate (6.11.2(d))

Monitor pressure

Monitor air flow rate

Sample at vent point after purge time

After satisfactory vent gas test, close purge gas (air) inlet valve vent and remove purge hose from vent. Seal all outlets

Do not allow to exceed original operating pressure. If correct flow rate cannot be achieved, abandon purge and use indirect method (Appendix 3)

Check purge is complete (Table 11).

Complete records and inform responsible person of position

FIGURE 10 - FLOWCHART FOR DIRECT PURGING OF GAS TO AIR



APPENDIX 1 : GLOSSARY, ACRONYMS, ABBREVIATIONS, SUBSCRIPTS AND SYMBOLS

UNITS,

GLOSSARY All definitions are given in IGEM/G/4 which is freely available:

 

as a CD, with the purchase of any IGEM Standard, upon request by downloading a printable version from IGEM’s website www.igem.org.uk.

Recommended and legacy gas metering arrangements are given in IGEM/G/1 which is freely available:

 

with the purchase of any IGEM Standard, upon request by downloading a printable version from IGEM’s website.

Downloading from the website ensures access to the latest version. ACRONYMS AND ABBREVIATIONS ACS ACoP DMIP DP ECV GB GM GRM GS(I&U)R GT HSE IV IGEM LDF LFL LPG LR MAM MIP MIOV MOP MOV MPLR NDT NG NRV OP PT PV RD PE SG SN/NVQ SP st SSV STD STP TTD TTP UKAS

Nationally Accredited Certification Scheme Approved Code of Practice design maximum incidental pressure design pressure emergency control valve Great Britain gauge movement gauge readable movement Gas Safety (Installation and Use) Regulations gas transporter Health and Safety Executive installation volume Institution of Gas Engineers and Managers leak detection fluid lower flammability limit liquefied petroleum gas leak rate meter asset manager maximum incidental pressure meter installation outlet valve maximum operating pressure meter outlet valve maximum permitted leak rate non-destructive testing Natural Gas non-return valve operating pressure purge time purge volume rotary displacement polyethylene specific gravity Scottish National/National Vocational Qualification Set point standard slam-shut valve strength test duration strength test pressure tightness test duration tightness test pressure United Kingdom Accreditation Service.



UNITS in m mbar min mm m3 m3 h-1

inch metre millibar minute millimetre cubic metre cubic metre per hour

SYMBOLS Q > 

flow rate greater than less than or equal to

ø

nominal diameter volume is valve (normally open) valve (normally closed)

V

regulator safety device appliance

A

`M

meter filter blanking device

d L

diameter length nitrogen

N2 SUBSCRIPTS c f m mi p t u

consumer fittings, etc meter meter installation pipe total upstream



APPENDIX 2 : REFERENCES Care needs to be taken to ensure that the latest editions of the relevant documents are used. A2.1

LEGISLATION

 

Gas Act 1986 (as amended by the Gas Act (1995) Health and Safety at Work etc. Act 1974 Note:

      

This applies to all work activities. It places general duties on employers to ensure, so far is reasonably practicable, the health safety and welfare of their employees and the health and safety of members of the public who may be affected by the activity.

Petroleum Act 1962 Confined Spaces Regulations 1997 Construction (Design and Management) Regulations 2007 Control of Substances and Hazardous to Health Regulations 2002 Dangerous Substances and Explosive Atmospheres Regulations 2002 Electricity at Work Regulations 1989 Gas Safety (Installation and Use) Regulations 1998 Note:

    

Management of Health and Safety at Work Regulations 1999 Manual Handling Operations Regulations 1995 Personal Protective Equipment at Work Regulations 1992 Pressure Equipment Regulations 1998 Pressure Systems Safety Regulations 2000 Note:

 A2.2

For cylinders etc., Carriage of Dangerous Goods (Classification, Packaging and Labelling) and Use of Transportable Pressure Receptacles Regulations 1996 (as amended), the Transportable Pressure Vessel Regulations 2001 may also be relevant.

Provision and Use of Work Equipment Regulations 1998.

HSE ACOPS AND GUIDANCE NOTES

  A2.3

These apply to domestic and commercial premises. For industrial premises, the requirements of these Regulations could be considered relevant in any investigation under the Health and Safety at Work etc. Act. The Regulations set out detailed requirements for gas installation work. In particular, they require that anyone carrying out such work must be competent to do so. They also prescribe circumstances in which a tightness test and purge must be carried out.

HSG48

Human factors in industrial safety. Guidance.

HSL56

Safety in the installation and use of gas systems and appliances. ACoP and Guidance.

BRITISH STANDARDS (ABBREVIATED TITLES)

 

BS 5482-1

Domestic butane and propane gas burning installations

BS EN 60079

Electrical apparatus for explosive gas atmospheres.



A2.4

IGEM STANDARDS



IGE/UP/1 Edition 2 RWA

Strength and tightness testing and direct purging of industrial and commercial gas installations

IGE/UP/1A Edition 2 RWA

Tightness testing and direct purging of small low pressure industrial and commercial gas installations

IGE/UP/1B Edition 2

Tightness testing and purging of Natural Gas installations

IGE/UP/2 Edition 2

Gas installation pipework on industrial and commercial premises

IGE/SR/22

  

Purging operations for distribution and storage

IGE/SR/23

Venting of Natural Gas

IGE/SR/24

Risk assessment techniques

IGEM/G/1

Defining the end of a network, meter installation, and installation pipework

 

IGEM/G/4

Definitions for the gas industry

IGEM/GM/7B

Electrical connections and hazardous area classification for gas metering equipment.

   

fuel

gases

in

transmission,



APPENDIX 3 : INDIRECT PURGING WITH NITROGEN An indirect purge is to be carried out only and if:

  

the direct purge has been unsuccessful a direct purge is unlikely to be achieved successfully for example where inadequately-sized purge points are fitted a risk assessment indicates that heavier-than-air gas has to be purged indirectly.

A3.1

If a direct purge has been unsuccessful, make the installation and the surroundings safe, before implementing fallback plans. Check the calculations, survey the installation and inspect equipment to endeavour to identify the cause of failure to direct purge. If the cause is identified and can be rectified, (for example following calculation error, block hose, closed valve, restrictive purge points etc.), the direct purge can be repeated. Note:

A3.2

Take additional care at purge gas vent point due as a flammable mixture may occur at a different stage in the operation.

Ensure the indirect purge is a complete displacement purge using volume based measurement of inert gas and vent gas testing. Pay particular attention to any dead-legs. Take precautions to prevent asphyxiation, especially in basements and confined spaces. Take precautions to prevent the purge gas entering the GT’s or any other distribution network.

A3.3

Start with the largest diameter pipe and progress to the smallest. Ensure a minimum volume of N2 (equal to 1.5 x IV) of the installation is available (see Table 12 and Appendix 4). PIPE NOMINAL SIZE (mm) 100 150 200 250 300 350

MINIMUM QUANTITY OF NITROGEN GAS PER 1 m LENGTH (m3) 0.013 0.03 0.05 0.08 1.12 2.16

TABLE 12 - MINIMUM QUANTITY OF N2 PER 1 m LENGTH OF PIPE A3.4

As a guide, a standard 1.5 m long nitrogen bottle usually has a capacity of 6.5 m3. The maximum flow rate through a high capacity single-stage regulator is, typically, 60 m3 h-1.

A3.5

The criteria given in Table 13 apply when testing the vent gas.

A3.6

Following the indirect purge, if hot work is to be undertaken, take care in case small pockets of gas remain in the pipe due to the effects of stratification or due to the effect of dead-legs.

A3.7

When undertaking any work following an indirect purge, take suitable precautions to account for the presence of nitrogen.



FUEL TYPE (GAS OR VAPOUR

Natural Gas Propane

SPECIFIC GRAVITY AIR = 1

0.6 1.5

FLAMMABILITY LIMITS LOWER UPPER FLAMMABLE FLAMMABLE LIMIT % IN LIMIT % IN AIR AIR

4.5 2.1

15.5 10.1

SAFE PURGE ENDS POINTS INDIRECT INDIRECT PURGE FROM PURGE FROM NITROGEN FUEL GAS TO TO FUEL GAS NITROGEN SAFE END SAFE END POINT POINT % GAS IN N2 % GAS IN N2 7.5% gas in N2 90% Fuel Gas 3.5% gas in N2 90% Fuel Gas

TABLE 13 - FLAMMABILITY LIMITS AND SAFE PURGE ENDS POINTS FOR INERT PURGE A3.8

Once the purge to nitrogen is complete, it is advisable to then purge to air and ensure the oxygen level is at least 20%.



APPENDIX 4 : CALCULATION OF TIGHTNESS TEST DURATION A4.1

INSTALLTION VOLUME (IV)

A4.1.1

General The estimation of IV involves surveying the whole of the section to be tested. Note has to be taken of the relevant dimensions of all components including any:

   

meter pipe fitting, including any regulator, bend, tee, etc . pipework exposed to direct sunlight or high temperature Note:

The tightness test result is valid only if the temperature of the section remains stable throughout the period of the test.

A4.1.2

Calculations

A4.1.2.1

The following formula can be used to calculate the total installation volume (IVt) (m3) of the section to be tested: IVt = IVm + IVp + IVf Note:

The IVt (m3) needs to be calculated to two significant figures with “rounding” being upwards only. It is not advisable to round the calculations of IV of individual parts of a section as this may cause the test to be more onerous than necessary.

A4.1.2.2

IVm, IVp and IVf can be calculated as follows: (a)

IV of meters (IVm) Use Table 14 or consult the meter manufacturer for any other meter. DESIGNATION OF METER

G4/U6 G10/U16 G16/U25 U40 G40/U65 G65/U100 U160 RD or turbine

IVm (m3) 0.008 0.025 0.037 0.067 0.100 0.182 0.304 0.79d2L*

CYCLIC VOLUME m3 ft3 .002 0.071 .006 0.2 .01 0.35 .02 0.71 .025 1.11 .057 2.0 .071 2.5 N/A N/A

BADGED RATING m3h-1 6 16 25 40 65 100 160 N/A

ft3h-1 212 565 883 1412 2295 3530 5650 N/A

* or equivalent length of pipe d = diameter, i.e of meter connection (m) L = length, i.e flange to flange dimension (m).

TABLE 14 - INSTALLATION VOLUME (IV) OF METERS



(b)

IV of pipe (IVp) For a 1 m length of pipe, obtain the volume of the particular pipe from Table 15. Multiply the value given by the length of the pipe in the section. NOMINAL SIZE OF PIPE (mm) (in) 25 32 40 50 65 80 100 125 150 200 250 300 350 Note:

VOLUME OF 1 m LENGTH OF PIPE (m3)

1 1¼ 1½ 2 2½ 3 4 5 6 8 10 12 14

.00064 .0011 .0015 .0024 .0038 .0054 .009 .014 .02 .035 .053 .074 .089

For sizes not shown, go to the next larger size given.

TABLE 15 - VOLUME OF 1 m LENGTH OF PIPE (c)

IV of valves, fittings, pressure vessels, accumulators, etc. (IVf) Add any additional volume caused by such components. In the event that IVf cannot be calculated, add an additional 10% of the pipe volume (IVp).

A4.2

TIGHTNESS TEST PRESSURE (TTP) TTP is equal to OP, see Sub-Section 5.3 for more information.

A4.3

SELECTION OF PRESSURE GAUGES

A4.3.1

The sensitivity of any pressure gauge determines the gauge readable movement (GRM). The gauges listed in Table 16 are typical of the instruments used for tightness testing and have to be used (for the gauges listed) to determine GRM. The list does not preclude the use of other types or ranges of gauge but the gauge used needs its GRM specified. Note:

If an inferential gauge is used then, to ensure accuracy, care needs to be taken regarding rounding errors caused by using the last decimal place.

TYPE OF GAUGE

Water (SG 1.0) High SG (SG 1.99) Electronic (1 decimal place) Electronic (2 decimal places) Electronic (1 decimal place) Note:

TYPICAL RANGE (mbar)

0 0 0 0 0

– 120 – 200 - 200 – 200 – 2,000

TYPICAL READABLE MOVEMENT (GRM) (mbar)

TYPICAL MAXIMUM TTD (mins)

0.5 1 0.5 0.1 0.5

Longer tightness test durations (TTD) are possible if an absolute gauge is used.

TABLE 16 - SELECTION OF PRESSURE GAUGES (typical data)


30 45 30 15 30


A4.3.2

When using a gauge, the following shall be undertaken:



for all gauges, refer to the manufacturer’s instructions for details but, in the event that no manufacturer’s instructions are available, calibrate the gauge at an interval not exceeding 12 months. A calibration certificate shall be available for any instrument used for tightness testing

  

ensure that any gauge is suitably ranged for the installation being tested ensure an adequate level of accuracy of any gauge ensure that, where necessary, any electronic gauge is certified for use in a hazardous area (see Sub-Section 3.4) and operated within the manufacturer’s specification with regard to ambient temperature



stabilize any electronic gauge at the temperature of the area where it is to be used for 30 mins, or as specified by the gauge manufacturer, prior to the test being carried out Note:



Electronic gauges are prone to drifting due to changes in ambient temperature changes.

if appropriate, zero any gauge at the start of the test at atmospheric pressure. Note:

Any movement from zero at atmospheric pressure at the end of the test invalidates the complete tightness test which then needs to be carried out again.

A4.4

MAXIMUM PERMITTED LEAK RATE (MPLR)

A4.4.1

An MPLR of 0.0014 m3 h-1 applies irrespective of the location of the installation. Note:

In the interest of simplification and taking account of the size of metering installations, new and existing installations have been treated the same.

A4.5

TIGHTNESS TEST DURATION (TTD)

A4.5.1

To calculate TTD, use the formula as given in A4.5.3. GRM and the factor F1 can be obtained from Table 16 and Table 17 respectively.

A4.5.2

TTD needs to be rounded up to the next full minute and not less than 2 mins.

A4.5.3

Table 16 specifies the maximum TTD for particular gauge types, which minimise the effect of normal variations in barometric pressure and ambient temperature. TTD = GRM x IV x F1 F1

=

as derived from Table 17 FACTOR F1

GAS TYPE NATURAL PROPANE

TEST USING FUEL GAS AT OP 42 102

TEST USING AIR OR NITROGEN AT OP 67 221

TABLE 17 - FACTOR F1 TO APPLY WHEN CALCULATING TTD



APPENDIX 5 : PURGING HEAVIER-THAN-AIR GASES – RISK ASSESSMENT A9.1

FLAMMABILITY RANGE Differing fuel gases have very different flammable ranges and, when working with these various gases, it is essential that the range is understood as well as having gas detection equipment suitable for the gas being monitored.

A9.2

DENSITY (SPECIFIC GRAVITY) The densities of gases vary dependant on their temperatures, so it is normal to refer to density relative to air. Air has a density of 1. Gases with lower density are lighter-than-air and gases with a higher density are heavier-than-air.

A9.3

PROPERTIES OF LPG The most common of the heavier than air gases in use are known as Liquefied Petroleum Gas, or LPG, (3rd family gases). BS 4250 is the specification for commercial butane and propane, but gases outside this specification are often used for special purposes. They are stored in the liquefied state under pressure. The actual pressure in the storage container, known as the vapour pressure, is dependent upon the specification of the actual LPG and the temperature of the stored liquid. These procedures apply only to the pipework downstream of the first stage pressure regulator in a vapour system. They do not apply to the storage tank, the high pressure pipework feeding the first stage regulator, or to any part of a system containing LPG in the liquid phase. LPG vapour is, normally, used for gas supplies to gas fired equipment. This vapour may be generated by natural vaporisation of the liquefied LPG, or for large industrial offtakes by the use of an in line vaporiser where the latent heat required is provided from an external source. Some LPG may contain small quantities of heavy hydrocarbons that do not readily vaporise, often described as "heavy ends". Where they are present, these heavy ends will concentrate in the bottom of storage vessels used for natural vaporisation systems, or in the base of external vaporisers. In abnormal situations, or where the plant operators fail to drain the system regularly, they may be carried over into the gas supply pipework. Where heavy ends are found in downstream pipework specialist advice is required to ensure that they are removed and disposed of in a safe manner. A permit to carry out such work is required to be issued by an authorised competent person. Note:

Heavy ends are, normally, only associated with LPG produced from refinery operations and are not present in LPG produced from natural gas liquids.


Back cover – Blank IGEM

IGEM-UP-1C Draft for Comment - 2nd Consultation (IGEM-TSP-10-122)

Recommend Documents