Host Pipe Factors

Host Pipe

The term "host pipe" describes the existing pipe that Duraliner™ will renew. There are properties of the host pipe that are very important to understand, such as material, physical dimensions, system properties, system temperature, and depth.

Material

The material type of the host pipe has little effect on the application of Duraliner™. Duraliner™ can be installed in all major water system material types, including cast iron, ductile iron, steel, cement-asbestos, concrete, etc. The host pipe must be cleaned to the appropriate inside diameter, and be free of sharp protrusions and points.

Physical Dimensions

The physical dimensions of inside diameter, outside diameter, and wall thickness must be known early in the project to be able to select the appropriate starting stock.

The inside diameter (ID) of the host pipe is critical for three reasons:

1. The starting stock selection is influenced by the ID because this dimension controls the outside diameter (OD) of starting stock that can be inserted in the host pipe. Generally, the starting stock OD selected is approximately 2" smaller than the host pipe ID. This has been shown by experience as the dimensional relationship necessary to assure successful insertion. This is especially important with longer runs of host pipe that may have sweeps and curves in the alignment.
2. The ID of the host pipe determines the amount of overall flow area reduction when Duraliner™ is installed. Duraliner™ flow characteristics are discussed in the Flow section, however in general, flow is not impeded, and in some cases, is improved.
3. In some cases, usually with larger diameter systems, the ID of the host pipe may determine the size and type of fittings that will be used to reconnect the host to its system.

The outside diameter becomes important when the starting stock is to be expanded to this dimension. It is common practice to expand Duraliner™ to the host pipe OD to allow standard host pipe fitting to be used in reconnection. This sets the maximum dimension that figures prominently into the operating pressure calculation for the Duraliner™ system (discussed the Strength and Operating Pressure section). The OD also determines the sizing sleeve needed to transition the Duraliner™ from the inside diameter to the outside diameter. The sizing sleeve is a custom-made fabrication required for installation.

Wall thickness is important to confirm because some wall thickness may be lost to corrosion, etc. This will be reflected in the expanded Duraliner™. Duraliner™ is installed whith a transition collar that provides a smooth expansion from host pipe ID to OD.

In general, cast iron and ductile iron dimensions will vary based upon age and type of material. Some background on the characteristics, history, and development of water pipe and materials is helpful in determining the host pipe material when records become unclear or nonexistent.

Cast iron dimensions are different than ductile iron. Ductile iron has a thinner wall and larger ID than cast iron. This is because cast iron is considered rigid for design purposes and ductile iron is considered flexible. Flexible pipe design principles take into account more properties of the material, allowing its true strength to be recognized.

Prior to 1902, there were no common standards for cast iron pipe--it was made to specific customer requirements. The American Water Works Association (AWWA) implemented the first national standard for cast iron pipe in 1908, with regional standards becoming the norm between 1902 and1907. Up until 1928, cast iron was pit cast. After 1928, centrifugal cast pipe became the standard. This cast method produced a more dimensionally uniform product.

In 1965, ductile iron standards were adopted. The oldest operating cast iron pipe is in France and was installed to provide water to the gardens at Versailles in 1664. Cast iron life has not been fully determined, but 100 years is normally accepted as its life span. Pipe installed prior to 1910 is deemed to have a life of 120 years, from 1911 to 1945, a life of 100 years, and after 1945, a life of 75 years.

The primary difference between cast and ductile is metallurgy. Ductile iron contains more magnesium and contains graphite in a nodule form. Cast iron contains graphite in a flake form. Cast iron usually has a larger wall thickness than ductile iron, and some classes of cast iron will have larger OD as well.

In some areas of the country, cast and ductile iron pipes are cement-lined. This is done to reduce the amount of reaction between metal and water that produces incrustation called tuberculation. Tubercules are normally cleaned out of a water pipe prior to insertion of Duraliner™ starting stock.

System Properties

The operating pressure of the host pipe system must be clearly understood because Duraliner™ starting stock is selected to meet the operating conditions of each installation. Duraliner™ can handle a wide range of operating pressures with applications of 200+ psi possible. Operating pressure of 150 psi for a municipal water system is standard, but pressures can vary greatly, with a range of 75 to 200 psi covering most of the cases UGSI has seen recently. Duraliner™ is sized to provide stand-alone pressure capabilities with no contribution from the host pipe.

It is not unusual for a system pressure to have been reduced over time to compensate for aged/worn components. The client preference may be to return the system to a higher pressure upon completion of rehabilitation. Duraliner™ can be engineered for future operating pressure considerations as long as they are understood early in the selection process.

UGSI will typically select the proper starting stock wall thickness to meet the operating pressure of each application. In this manner, the most cost-efficient material will be used. Both CIOD and IPS sizes are used for starting stock.

Host pipe system temperature

Municipal water systems are considered to operate at ambient temperatures, defined in standards as 73.3° F (23°) C. PVC strength capabilities diminish as temperatures rise above ambient. The operating temperature can be other than ambient in some isolated cases, and this possibility must be recognized very early for starting stock selection. An example could be where the pipe being renewed carries water that is pulled from a heated aquifer and then cooled before distribution.

Depth

The depth of the host pipe determines whether the starting stock is fused above ground or in an access pit. Normal depth for a host pipe is approximately 4 feet. Most starting stocks can be fused above ground, and pulled in continuously at this depth. As the pipe insert location becomes deeper, fusion may move from above ground into the pit, which is a significant change to normal operating practice. Length of starting stock may change as a result.

Below a depth of 4 1/2 feet, shoring is required for proper bracing of the excavation. Depth in relation to the water table will also play a role in defining the host pipe because Duraliner™ should be inserted and expanded in a relatively dry pit. Some expansions have been done in a flooded host, with the access pits kept free of water. A dewatering operation may have to be considered if the water table is above the host pipe invert.