How to install and maintain low pressure gas installation pipework

Peter Mason of Blue Flame Associates Ltd reviews the significant proposed changes to BS 6891 – Specification for the installation and maintenance of low pressure gas installation pipework of up to 35mm (R1¼) in premises.

Arevised British Standards Institution (BSI) standard, BS 6891:2013, is currently in the ‘draft for comment’ stage.

The revised standard is intended to replace BS 6891:2005, and the relevant parts of BS 5482–1:2005. The revised standard is intended for use by those involved in the design, installation, commissioning and maintenance of gas installation pipework (both natural gas (NG) and Liquefied Petroleum Gas (LPG)) up to 35mm or 1¼ inch steel pipework. The pipework may be installed in premises including residential park homes with a maximum flow rate of 16m 3/h (a U16 or G10 gas meter).

Table 1. The scope of pipework covered by BS 6891:

Gas

Pipework

Maximum pipe diameter

Operating pressure (mbar)

Natural gas

Downstream of the primary meter installation to the inlet of any appliance isolation valve or a self-sealing connector of a flexible connection.

R1 ¼ steel DN 32 PE

DN 35

21

LPG

Downstream of the ECV located on the outside of the property where no meter is fitted.

Downstream of the outlet of the final regulator where located downstream of the ECV.

Downstream of the outlet of the final regulator where located downstream of any cylinders.

Downstream of any primary meter installation.

(to the inlet of any appliance isolation valve or a self-sealing connector of a flexible connection).

R1 ¼ steel DN 32 PE

DN 35

37 (Propane)

28 (Butane)

The following pipework is excluded from BS 6891:2013:

  • Service pipework and distribution systems
  • Pipework operating at pressures greater than those in the above table
  • Pipework within an appliance
  • Bulk storage vessels
  • Caravans, recreation vehicles and leisure accommodation vehicles
  • Mobile heaters (LPG)
  • Catering installations to BS 6173.

Terms and Definitions

These have been significantly expanded to include:

  • New technologies
  • Revised terms and methods for buildings and building constructions
  • Additional scope (inclusion of LPG)
  • Changes to working practices

Some of the original terms and definitions are subject to minor detail change:

Emergency Control Valve (ECV) – now includes service pipework to address the inclusion of LPG.

Duct – an enclosed space specifically designed and constructed for the passage of building services.

Intermediate joisted floor – now known as an intermediate floor.

Protected shaft – now referred to as a protected area consisting of either a common stairway, corridor or lobby providing an escape route or a service shaft or duct which may contain electrical and water services.

Sleeve – protective gas tight pipework forming an annulus embedded in the structure through which pipework can be inserted and withdrawn.

Competence – updated to reflect the standard BS competence definitions including the requirement for individual’s knowledge to be kept up to date with changes in law, technology and safe working practice.

Competence requirements by country are also listed.

Design and planning

Exchange of information – a minor change to the requirement to tightness test installation pipework before covering adds ‘painted’ to the other covering methods.

Pipe sizing – changes to the requirements for all pipework mean that the gas must be at a suitable pressure at the inlet of any gas appliance to ensure that it meets the required appliance input. Pipe sizes may be calculated using the methods in Annex A.

The maximum pressure loss for all pipework must not exceed 1 mbar for:

  • New installations
  • Pipework modifications or extensions
  • Installation of a new appliance
  • Increasing the heat input of an existing appliance.

The maximum heat input of a range-rated appliance must be considered when sizing pipework to meet the requirements.

For a variable-rated appliance, the system heat input requirements need to be established to ensure that the pipe size is adequate.

All connected appliances need to be considered when calculating pipe sizes.

Natural gas – Although the meter and pressure regulating installation (PRI) are outside the scope of BS 6891, it is the responsibility of the designer or pipework installer to ensure that the meter and regulator is of sufficient capacity for the existing or proposed installation.

The design pressure drop between the outlet of the primary meter installation, and any appliance inlet must not exceed 1 mbar at the required installations flow rate.

Liquefied Petroleum Gas (LPG) – Although not normally the responsibility of the pipework designer or installer, the storage vessel, service pipework, regulators, meter and other supply equipment needs to be confirmed to be of sufficient capacity for the existing or proposed installation.

The design pressure drop between the outlet of the ECV or the outlet of the final stage regulator when fitted after the ECV, and any appliance inlet must not exceed 1 mbar at the required installation flow rate.

Materials – pipes are now referred to as tubes. Corrugated stainless steel tube (CSST) is now referred to as pliable corrugated tubing.

References to the standards concerning the manufacture of tubes and fittings have been updated to reflect changes in the original manufacturing standards – many of which have been superseded by European (EN) versions of the original standards.

Copper compression fittings are now referred to as mechanical fittings – the definition of which is a joint in which gas tightness is achieved by compression (with or without a seal) and that can be disassembled and reassembled.

Jointing materials need to conform to BS EN 751 and BS 6956.

Valve lubricants need to be suitable for use with the fuel in use.

LPG plug valves need to be spring-loaded.

Jointing – new statements include:

  • Joints need to be made in such a manner as to avoid undue stress on the fitting.
  • Pipework ends need to be square-cut and de-burred.
  • Finished joints need to be visually inspected for defects.
  • All joints must be mechanically strong and gas tight.

Union joints need to be of the ground face or compression type. Pliable corrugated tubing and fittings need to be assembled and installed in accordance with the manufacturer’s instructions.

Installation

New general statements include:

  • Pipework needs to be installed so as not to impair the structural stability, fire resistance, damp proof course, or thermal and sound insulation of the building.
  • Pipework needs to be situated such that, in the event of a gas escape, gas is not capable of entering cavities within the structure where the gas escape could remain undetected.
  • Pipework must not be installed in any location where any future maintenance could affect the structural stability of the building.

Safety precautions

These have been included as a sub-section and involve the application of a risk assessment prior to any work being carried out on the pipework installation.

The possibility of stray electrical currents and voltages now needs to be determined.

The use of a voltage detector on exposed metal parts may help to identify harmful voltages but is not designed to detect current flow. If there is any doubt regarding the safety of an electrical installation, a competent electrician should be consulted.

A further risk assessment is required to determine whether work on a temporarily-isolated installation that may contain fuel gas is safe.

A revised procedure has been included to cover occasions where there may be a risk of gas in the pipework being ignited when using a blowlamp:

  • Carry out a tightness test to IGE/UP/1B and ensure that the isolation valve is not letting-by.
  • Disconnect the gas supply to the installation or section.
  • Remove any meter from the installation or section.
  • Seal all gas ways with an appropriate fitting.
  • Increase ventilation in the work area.

A risk assessment needs to be carried out when decommissioning an installation to determine whether fuel
gas needs to be purged from the installation.

Pipework that is no longer required should be disconnected as close to the live supply as possible. Pipework must be sealed with appropriate fittings, and parts that may still contain fuel must now be labelled.

Pipework must not be installed in a ventilation or air-conditioning duct and must be physically spaced from other services.

Main equipotential bonding is known as a main protective bonding conductor. The requirements for connection are:

  • Connected to fixed rigid pipework.
  • Located as near as is practicable to the point of entry into the premises.
  • Located before any branch in the pipework.
  • Positioned where it is accessible, can be visually inspected and fitted with a warning label stating ‘Safety electrical connection. Do not remove.’
  • Fixed with a mechanically and electrically sound connection that is not subject to corrosion.

A recommendation for temporary continuity bond construction is now included. The temporary continuity bond should be at least 1.2m long flexible cable of at least 250V AC rating, feature a cross-sectional area of not less than 10mm2, be of multi-strand construction and have a robust clip or clamp firmly attached at
each end.

AECV requirements remain unchanged. An accessible AECV is now regarded as one that is installed at a height not greater than 1400mm.

Pressure test point requirements are essentially unchanged apart from the consideration that the test point location should allow for ease of tightness testing.

A pressure test point must be installed when one is not provided on an appliance. The point may be incorporated with the appliance isolation valve.

Sleeves

There are significant changes to this section because pipework passing through a wall or a floor, whether or not it contains a cavity, must now pass through a sleeve.

The material used for sleeves needs to be:

  • Resistant to corrosion
  • Impermeable to gas – e.g. copper, steel, polyethylene (PE) or polyvinyl chloride (PVC)
  • Capable of protecting the pipework against failure caused by movement of the structure.

No sleeve may have joints along its length.

Where pipework is required to be enclosed in a sleeve, the factoryapplied coating or covering is not deemed to be adequate. Sleeves must pass through the full width of the wall or the full thickness of the floor.

The outside of the sleeve must be secured and sealed at each end to the structure of the building with a suitable building material – e.g cement mortar.

Sleeves must not impair the structural stability, fire resistance, thermal and sound insulation of a building. The annular space between the pipework and the sleeve needs to be sealed at one end to the pipework with a flexible fire-resistant compound.

Where a sleeve passes through an exterior wall, the sealing of the annular space between the pipework and the sleeve must be on the inside of the wall.

The internal diameter of any sleeve should allow for an annular space around the pipework to enable satisfactory insertion and withdrawal of the pipework and to allow adequate sealing between the pipework and the sleeve.

Screwed, push-fit and mechanical joints must not be located on the pipework within a sleeve.

Pipework support

A new pipework support table reflecting larger pipe diameter support intervals is introduced.

There is now a requirement to use supports to prevent pipework coming into contact with surfaces that may cause corrosion.

Pipework locations

Changes to the requirements mainly reflect the inclusion of LPG in the standard. Advances in construction practices are also considered.

LPG pipework installed in a void without sufficient adventitious ventilation needs ventilation to be provided at low level. Ventilation rates and cross-sectional areas remain unchanged.

Solid timber joists less than 100mm or greater than 250mm may not be notched unless deemed acceptable by a
structural engineer.

Pipework may not be installed within a compartment floor that separates dwellings.

If pipework is installed in roof spaces, roof rafters, purlins, trussed rafters and bracing may only be notched if approved by a structural engineer.

Roof spaces without specific ventilation provision must be treated as unventilated voids for gas pipework installations. At least two ventilators must be installed of at least 50cm2 each.

Pipework must not be laid below or within the roof space insulation material.

Pipework buried in solid floors must run in the direction of the walls.

Pipework must not be buried in power-floated floors forming part of the structure.

Pliable corrugated tubing buried in a floor screed should conform to BS EN 15266 or BS 7838.

Pipework within acoustic floors may only be installed with the agreement of the designer.

Pipework within walls must take the shortest practicable route – horizontally or vertically. Diagonal
pipework runs must be avoided.

Where copper and pliable corrugated tubing is installed between wall battens and within 50mm of the plasterboard face, it needs to be protected against penetration with a steel plate 1mm thick.

The section on timber and light steel framed partition walls has been expanded to cover protection of pipework installed within 50mm of the surface.

Restrictions on the amount to be notched from bottom plates of wall frames and sole plates mean that no more than one third of the width of the plate may be removed. Several new drawings have been included to address
the installation requirements and restrictions for pipework in timber and light steel framed walls.

Buried external pipework must be corrosion resistant or adequately protected against corrosion. The section covering buried pipework is now extensive and includes the following aspects:

  • Soil types and their corrosive effects
  • Resistance to the loads imposed by any backfill
  • Assessment for pipework condition and periodic tightness testing
  • Metallic pipework – consideration of damage to protective coatings by backfill (unless installed within a sleevetype outer cover)
  • Joints – kept to an absolute minimum and readily accessible (except for welded joints or PE fusion welds)
  • Mechanical fittings must not be installed below ground.

Depth of cover for buried pipework is shown in Table 2.

Burying concrete slabs below ground level at approximately 100mm above the pipework may suffice when ground conditions do not permit the full depth to be excavated.

Buried pipework must be identified by the use of yellow marker tape buried 100mm to 300mm above the pipework.

Above ground external pipework must be protected against the risk of mechanical damage.

PE pipework may only be used outside and must be buried except for short risers for entry into a building.
Where the PE pipework is exposed to daylight, it needs to be shrouded and protected against mechanical damage. Pipe must be fusion welded by a competent person.

Ventilation

  • Ventilation openings must lead to a safe place – preferably outside.
  • Ventilation openings must allow air movement to occur in a duct.
  • Ducts must be sealed from cavities, walls or floors that they pass through.
  • The fire resistance of any pipe duct needs to be equal or greater than any void through which it passes.

Multi-occupancy buildings

Any pipework passing through any building other than the one it supplies with gas needs to be located in a purpose-provided duct designed to prevent damage to the pipework.

Protected areas

Pipework passing through a protected area needs to be one of the following options:

  • Steel pipework with screwed joints
  • Steel pipework with welded joints
  • Copper pipe with no joints
  • Pliable corrugated stainless steel with no joints

A protected area needs to be ventilated at high and low levels direct to outside air (mechanical ventilation may not be used).

If pipe in a duct has an inspection opening into a protected area, the opening must be sealed on all edges to prevent gas escaping into the protected area.

Pipework inside timber framed and light steel framed buildings

If pipework is to pass through a vapour control layer, the hole cut in the layer needs to be as small as possible to prevent gas passing through. A hole in the VCL must be made good with adhesive tape.

No air movement is allowed into the inner leaf framework.

Allowance for movement or shrinkage between two wall structures may be made with a length of pliable corrugated tubing installed within a length of PE pipe, which is sealed to the wall at both ends and sealed to the gas pipe at the inside only.

Protection against corrosion

Principal changes are that electroosmotic damp proofing systems are covered and, in such cases, metallic pipework should be above ground level.

Carbon steel pipework may not be used below ground.

Buried pipework should preferably be installed without joints where practicable.

Commissioning

If an appliance is range or variable rated, the installer needs to permanently mark on the data badge the heat input at which the appliance is to be set.

After work, the installation needs to be tightness tested and purged in accordance with IGEM/UP/1B.

Meter and regulator installations (both NG and LPG) need to be installed and commissioned in accordance
with the relevant standard.

Pipe sizing needs to be checked when appliances are connected.

Maintenance

Following commissioning, the responsible person has a duty to ensure that pipework is maintained in a safe condition. Filters, if fitted, need to be periodically cleaned.

Annexes

Annex A addresses pipe sizing procedures for both NG and LPG Annex B provides information regarding sulfidation of NG installations and recommends solutions such as filtration or the use of alternative materials to copper.

Annex C details the rationale regarding ‘Gas in Intermediate floors’ for NG installations only.

Annex D defines protected areas according to the Building Regulations in both England and Scotland.

Annex E is normative and details the requirements for LPG final stage regulators and safety devices:

  • The installation needs a regulator with overpressure shut off and a limited relief no greater than 5% of the regulator capacity.
  • Regulators need to be installed in accordance with the manufacturer’s instructions.
  • The regulator and safety device needs to be located as near as is practicable to the ECV or AECV outlet.
  • Devices should be pre-set and deliver an operating pressure listed in the table within Appendix E.1.

Location of LPG regulators

Information contained in BS 5482-1 and BS 6400-3 has been incorporated into Annex E.

Regulators and other controls must be mounted above the level of the cylinder valves.

Regulators connected downstream of an ECV or AECV need to be connected as near as possible to the ECV/AECV.

Vent tips need to be kept away from ignition sources and the possibility of blockage, water ingress and interference.

Vent holes and limited relief valve outlets must be protected against water ingress, blockage and allow for drainage.

Regulators with a relief valve must not be located within a building.

The limited capacity relief valve must be positioned so that the vent is located according to the proximity distances listed in Appendix E and BS 6400-2/3.

Table 2. Depth of cover for buried pipework:

Pipework location

Depth (mm)

Private gardens including pathways (no vehicular traffic)

375

Private drives with light vehicular traffic

450

Private drives where there is a likelihood of heavy traffic (LPG road tankers)

600

Other fields and agricultural land

1100

Other private ground

600

To sum up

Principle changes are:

  • Redefining of terms and adoption of new building methods.
  • Recognition that pipework needs to be maintained in a safe condition.
  • Inclusion of LPG pipework and pressure controls.
  • Use of metallic pipework below ground is discouraged.

The standard should be consulted if further clarification of the numerous changes is required.