BS 6891:1988 download.Specification for Installation of low pressure gas pipework of up to 28mm (Ri) in domestic premises (2nd family gas).
1 Scope
BS 6891 specifies design parameters, materials and methods of installing steel or copper low pressure gas pipework, in sizes not exceeding DN 25 or 28 mm respectively for the supply of 2nd family gas in domestic dwellings. This standard applies to low pressure gas installations having a maximum pressure of 75 mbar’(30 in w.g.).
COMMENTARY AND RECOMMENDATIONS on clause 1.
Steel pipework of nominal size DN 25 is that size which is threaded to RI in accordance with BS 21. The provision of service pipes to the consumer’s gas meter is covered by the Institution of Gas Engineers’ Recommendations IGE/TD/4: Edition 2.
The installation of low pressure gas meters (2nd family gases) is covered in BS 6400. Liquefied pet roleuin gas installations are covered in
BS 5482.
Installation pipework in larger sizes or at higher gas pressures are detailed in British Gas publication
IM/16.
Gas, as defined in BS 1179, is normally supplied to the public in accordance with statutory requirements. The provisions of this standard apply to installations supplied with 2nd family gases including natural gas and mixtures of liquefied petroleum gases (LPG) and air.
NOTE The titles of the publications referred to in this standard are listed on the inside back cover.
2 Definitions
For the purposes of BS 6891 the definitions given in BS 1179:1967 and in BS 1179-6:1980 apply, together with the following.
2.1
installation pipes
that or any part of the installation pipework from the first fitting or joint after the primary meter outlet union connection to points at which appliances are to be connected
COIMENTARY AND RECOMMENDATIONS on 2.1. This definition varies from that given in the Gas Safety (Installation and Use) Regulations 1984
2.2
duct
a purpose designed enclosure to contain gas pipes and having a cross-sectional area greater than 10 000 mm2
COMMENTARY AND RECOMMENDATIONS on 2.2. This definition is in accordance with BS 8313
2.3
emergency control
a cock or valve for shutting off the suppiy of gas in
an emergency
COMMENTARY AND RECOMMENDATIONS on 2.3. The application of such valves is given in 7.11
2.4
meter control
the valve fitted upstream of, and adjacent to, a meter to shut off the supply of gas to it
COMMENTARY AND RECOMMENDATIONS on 2.4. This defines the term “meter control” in relation to a primary meter. A similar control may be fitted before the inlet to a secondary meter (see BS 6400)
2.5
primary meter
a meter connected to the service pipe, the index reading of which constitutes the basis of charge for all gas used on the premises
2.6
service pipe
a pipe connected to a main to provide a supply of gas to one or more consumers and terminating at and including the primary meter control(s)
2.7
sleeve
a duct, tube or pipe embedded in the structure for the reception of an installation pipe
3 Exchange of information and time schedule
3.1 At the initial stages of building design and planning the interested parties shall verify that the installation pipes will be adequate for both immediate and probable future requirements.
A time schedule for fixing the installation pipes shall be agreed as early as possible and any subsequent changes be notified to interested parties at the earliest opportunity.
3.2 All necessary information regarding the routing of installation pipes and positions of controls and installation points to serve the appliances shall be made available to those concerned as early as possible by means of drawings, specifications and consultations.
COMMENTARY ANI) RECOMMENI)ATIONS on 3.2. The drawings should also include:
a) the position of ducts and chases when installation pipes are to be concealed;
b) special requirements of a precautionary nature, e.g. limitations on proximity to other services;
c) sizes and materials and position. of all installation pipes and controls.
3.3 Any installation pipe fitted as erection of a building progresses, and which will subsequently be inaccessible, shall be tested for soundness before being buried, covered or wrapped.
3.4 Any work to be done by the gas installer that requires attendance by other trades shall be clearly defined.
4 Design considerations
4.1 Sizes
4.1.1 When designing an installation, the sizes of all installation pipes shall be determined from the maximum gas rate of the appliances to be connected, allowance being made for the maximum demand likely to occur at any time.
COMMENTARY AND RECOMMENDATIONS on 4.1.1.
Allowance should also be made for the possibility of future extensions, especially if the pipes are to be buried. Appendix A gives a method of calculating pipe sizes in a system.
4.1.2 The pressure drop between the outlet of the meter and the points to be connected shall not exceed 1 mbar at maximum flow conditions (see Table 1 and Table 2).
Where wrapping tape is to be applied, the pipe should he clean, dry and prepared in accordance with the manufacturer’s instructions. An overlap of greater than 50 % should be used to provide a protective layer or double thickness.
Where possible, wrapping should be coloured yellow ochre in accordance with BS 1710.
Some pipe sheathing and wrapping tapes suffer from colour fade and surface cracking when exposed to direct sunlight.
Copper pipe should not be located where it is liable to be subjected to temperatures in excess of 100 °C.
8.1.2 Pipework in fireplace openings shall be factory sheathed and/or wrapped on site.
COMMENTARY AND RECOMMENDATIONS on 8.1.2. Soot and debris can be highly corrosive.
8.1.3 Assembled pipework shall be tested for soundness in accordance with clause 9 before any additional protection against corrosion is applied on site.
8.2 Buried pipework
8.2.1 Internal environment
8.2.1.1 Pipework that is to be buried in a solid floor or wall shall be factory wrapped or sheathed or protected on site by wrapping or suitable additional bituminous paint protection.
The entire section of pipe and fittings to be buried shall be protected. Any sheathing or wrapping shall be examined for cuts or other defects and made good prior to use. Joints and fittings shall be cleaned and wrapped or bituminous painted after the satisfactory completion of the soundness test.
Galvanized or painted pipes shall not be buried without additional protection as previously specified.
COMMENTARY AND RECOMMENDATIONS on 8.2.1.1.
Protective measures are applied as a precaution against electrolytic and/or chemical corrosion. The use of factory bonded wrapping or sheathing is recommended.
8.2.1.2 Where installation pipes are to be buried in magnesium-oxy-chioride cement or magnesite flooring, they shall be of copper, with a factory bonded sheath and jointed with copper capillary fittings.
Bends and joints shall be further protected by wrapping with a suitable plastics tape. All surfaces shall be clean and dry before the additional protection is applied with a 50 % overlap to provide a layer of double thickness.