Department of water affairs and forestry technical guidelines for the development of water and sanitation infrastructure

13.21Structural design

Pipelines should be designed for internal and external pressure including surge pressure.

The structural load bearing capacity of the pipe is specified by the manufacturer and care should be taken not to expose the pipe to loading conditions other than that intended by the manufacturer.

13.22Corrosion protection

Refer to DWS 1131 in Specifications Folder.

13.23Couplings

Two major categories are generally used, namely rigid and flexible joints.

Flexible joints are defined as those joints that allow some telescopic movement or angular flexure of the adjoining pipes.

13.23.1Rigid couplings/joints

13.23.1.1Flanges

Flanges should be attached to pipes by metal-arc welding, the weld preparation being in accordance with the requirements of BS806 Type 6 unless otherwise specified.

A slip-on welded flange is suitable for all design pressure conditions covered by BS flange tables up to and including Table J and design temperatures not exceeding 425^oC, with pipes 80 mm and over.
Flanges should be in accordance with BS 4504.

13.23.1.2Welded butt joints

Butt joints welded by the metal-arc process should be in accordance with the requirements of DWS 1130 and DWS 1110.

13.23.1.3Screwed couplings

Pipes should be screwed taper and sockets parallel thread according to SANS 1109 or ISO 7/1.

Galvanized pipes may be threaded after galvanizing.
The use of parallel threads on light pipes are not recommended.

13.23.2Flexible couplings

All flexible coupling should be able to withstand an internal pressure equal to or greater than the design working pressure of the pipe.

The couplings should be able to withstand any external pressure due to installation conditions without the presence of an internal pressure.
Spigot and socket joints utilizing a rubber ring as a seal should be watertight under working pressure with a shear force equal to the expected external load applied to the coupling.
Rubber O-rings used for sealing should not elongate more than 25% of the original length when stretched over the spigot end of a pipe. See BS 2494.
Rubber o-rings should not be exposed to ultra-violet radiation or ozone for periods longer than the time required for installation.
Where a pipeline is likely to be subjected to any abnormally corrosive condition, the pipe manufacturer should be contacted in advance so that they may advise on the suitability of their joints for the purpose, or alternatively in collaboration with their rubber supplier, provide rings that will meet the requirements of the situation.
Sleeve type joints using a flexible plastic sleeve must conform to the misalignment test according to the relevant SANS standard for that specific type of pipe utilizing the coupling.
The draw and slew movement of the coupling will be in accordance with the requirements of the relevant SANS standard for that specific type of pipe utilizing the coupling.

13.24Fittings

13.24.1Reducers / diffusers and inlets

The range of angle of deflection for concentric or eccentric diffusers (enlarging diameter) should be between 2,5 – 30 degrees.

Where available NPSH is a problem, rounded inlets should provide better flow characteristics and less friction losses.

13.24.2Bends

Refer to DWS 1130.

Elbows should not have a bending radius smaller than the outside diameter of the pipe.
Medium and long radius bends should not have a radius larger than seven times the outside diameter of the pipe. Long radius bends normally have a radius of approximately three times the outside diameter of the pipe.
Standard angles of elbows are: 90, 45 and 22,5 degrees.

13.24.3Dividers

All flow dividers will cause change in flow direction and should therefore be properly anchored.

Standard angles of deviation from the main pipe are: 90, 60, 45, 22.5 and 11 degrees.

13.24.4Puddle or thrust flanges

Puddle or thrust flanges should be provided where a pipe passes through a water retaining structure or chamber.

A thrust flange will assist in the transfer of axial pipe forces due to water hammer or surges.

The flange should be designed structurally to withstand the shear forces it will experience.

Steel pipelines should be insulated with paint where they pass through concrete.

13.24.5Reinforced specials

The procedures developed H.S. Swanson et al have been incorporated into AWWA M11 - Steel pipe - A guide for design and installation, and are generally used in the design of reinforced specials.

13.25Pipeline specifications

The following DWAF specifications are applicable to pipelines and are included in the Specifications Folder.

NUMBER	DESCRIPTION
DWS 1110	Construction of pipelines
DWS 1130	Design, manufacture and supply of steel pipes
DWS 1131	Lining and coating of steel pipes and specials
DWS 1140	Design, manufacture and supply of asbestos-cement pressure pipes and joints
DWS 1150	Glass reinforced plastics (GRP) pipes and joints for use for water supply
DWS1160	Design, manufacture, supply, and installation of Polyvinyl Chloride (PVC) Pressure Pipes and fittings
DWS 2510	Supply of valves