Vitrified Clay Pipes

Clay pipe system features

General

All types of pipes used in the water and sewerage industry are subjected to an appraisal and approval system by various Authorities and meet Australian and International Standards.

In this presentation on Hepworth Clay Pipe Systems the focus is on features that exceed the requirements and which bring specific benefits to the specifier, user and asset owner.

Hepworth International has developed world’s best practice production processes to produce its SuperSleve Pipes from blended, fine ground clay fired in automatic continuous roller kilns. It is the only calsined clay pipe made from material ground to 0.25mm available on the Australian market. The process results in a pipe of longer length, more than one third lighter than conventional clay spigot and socket pipe and with consistent dimensions and straightness. These and other characteristics will give specifiers, users and asset owners a much greater degree of comfort in the control of problems such as root intrusion and infiltration which have been of major concern in sewerage systems.

Hepworth International is the world’s largest supplier of clay pipe and fittings and is recognised internationally for its innovation and solutions to problems to satisfy market demands.

Root Intrusion

The major factors involved in the control of root intrusion are:

Dimensional Tolerances

Past and current Australian manufacture of clay pipes involve the curing and handling of the pipes through vertical kilns. This process can produce variable dimensions through the length of the pipe including the jointing ends. Hepworth’s production process through continuous roller kilns produces a pipe with consistent dimensions and of low tolerances throughout the length of the barrel. The barrel can be cut at any point and used directly with the coupling with a guarantee that the ring pressure and contact area are not compromised. Austral Pipes’ laboratory conducted the following measurements on ten (10) pipes each of 100mm and 150mm diameter:-

Facet Standard Requirement Actual
Internal diameter DN100 - 97 to 103mm
DN 150 - 147 to 153mm		 DN100 - 99 to 100mm
DN150 - 148 to 149mm
Length +2 - 1% of stated length Less than -0.3% on 1.75m
Straightness Maximum permissible Deviation: 7mm on 1.75m 0.7mm on 1.75m length average
Spigot & socket size tolerance +/- 1.6mm +/- 0.5mm
End squareness Tested in accordance with App D
DN100 - 2mm
DN150 - 3mm		 DN100 <1mm
DN150 <1mm

The production process produces pipe with dimensional tolerances that are world’s best. These tolerances together with the smoothness of the pipe ensure that ring pressures are maintained throughout the circumference of the ring even when the pipe is joined at cut ends and such ring pressure ensures consistent moisture prevention barrier to deter root intrusion.

Rubber Ring Interface Pressure

Hepworth SuperSleve Pipes are joined with a Polypropylene Coupling which are manufactured to ISO 175. Polypropylene retains its properties better than PVC at high temperatures, with a quoted maximum of 100oC compared with 60oC for uPVC. The coupling is not designed to restrain the two pipe ends when they move due to ground movements but instead follows the movement and maintains the seal and so very little stress is imposed on the material or indeed on the pipe ends.

The performance capability of the sleeve joint far exceeds the standards and hence ring pressures are retained over a far greater range to maintain a watertight seal and consequently inhibit root intrusion.

The sleeve joint has been tested to 10 metres head with specified draw and deflection without leakage and thus is suitable for sewers designed for intermittent surcharge to optimise asset performance.

Facet Standard Requirement Actual
Joint deflection 3 degrees 6 degrees at 6m head
Line displacement 6mm at joint 10mm at 6m head
Withdrawal 10mm withdrawal 20mm at 6m head

Because of root intrusion problems in the Australian environment, the Australian Standard has imposed very stringent requirements on ring interface pressure and contact area.

The test results as detailed in Attachment 5 show the compliance to this Standard by Hepworth SuperSleve Pipes viz:

“The tests described here show that all the SuperSleve coupling seals create sealing pressures on the pipe which are in excess of the test requirement of 5.5 bar (0.55 MPa) of section 6.3.1 of Australian Standard AS 1741. The contact widths measured are also in excess of the 7mm requirement in the same standard”.

Porosity

Past and current Australian clay pipes have been made with clays and shales ground to a maximum allowable 2.25mm particles. Hepworth SuperSleve Clay Pipes are made from calsined materials ground to 0.25mm particles. This has led to a dense, thinner walled pipe which far exceeds Standard requirements for crushing and flexural strength.

Facet Standard Requirement Actual
Crushing strength DN100 - 39 kN/m
DN150 - 39 kM/m		 DN100 - 57 kN/m
DN150 - 57 kM/m
Flexural strength DN100 - 2.0 kN/m
DN150 - 5.0 kM/m		 DN100 - 5.45 kN/m
DN150 - 12.13 kM/m

Thus the pipe is much more tolerant to variability in construction techniques, ground movement and bedding quality when compared to conventional clay pipes and thus crushing is reduced and consequently root intrusion through the damaged pipe.

Of major importance in the restriction of root intrusion into a sewerage system is the prevention of a moist environment around the pipe so that roots are not attracted to the pipe surround. Because of the fineness of the clay material used in the manufacture of Hepworth SuperSleve Pipe, the finished product has a water permeability that is barely measurable, refer Attachment 7. The Australian Standard permeability test has been tightened over the years because of the necessity to reduce this moist environment around the pipe. It is still relatively high to suit the larger clay particle size and production processes used in Australia.

Facet Standard Requirement Actual
Permeability 0.25m max per hour per mm diameter per metre length DN100 - 0.03
DN150 - 0.01

The features of Hepworth SuperSleve Pipes in restricting root intrusion offers the asset owner a lower long term maintenance cost in clearance of blockages compared to conventional clay pipes. Because of the stiffness of the SuperSleve coupling and the rigidity of the supporting clay pipe, there is no possibility of differential deformation between spigot and socket which is a possibility in uPVC pipes. Hence, the asset owner can also expect lower maintenance costs in the clearance of blockages for a SuperSleve clay pipe system over a uPVC pipe system. In the long term as uPVC pipe ages and becomes brittle, clearance of blockages by power rodding and high pressure jetting techniques will be compromised.

Infiltration and Leakage

Infiltration and leakage occurs at cracks, joint breakages or sealing deficiencies and at manhole connections.

The strength of the Hepworth SuperSleve Pipe and flexibility of the joint are more tolerant to variability in construction techniques and ground movement and hence offer the asset owner more comfort in its long term performance in environmental control and reduction of treatment costs because of this reduction in infiltration.

Of particular concern has been the infiltration and leakage at manhole joints. Clay is an inert, rigid pipe compatible with concrete and thus joints with concrete at entry and exits to inspection/maintenance chambers will remain secure in the long term. Such is not the case with uPVC or polythene pipe even if grit coated at chamber connections as the joint is compromised as the plastic deflects and deforms.

Pipeline System

Hepworth International is the world’s largest supplier of pipe systems for the sewerage market and can offer the most appropriate clay, plastics and fibreglass solutions for the specific environment eg mining subsidence conditions, particular trade wastes etc.

There has been a paradigm shift in requirements for access inspection and maintenance chambers. Technology in video inspection equipment, power rodding and high pressure jetting for clearance of blockages has improved and will continue to improve over the years to the extent that person access to chambers is now not a mandatory requirement by some Authorities.

Rehabilitation of sewers especially for clay pipes which may be some 100 years after initial construction should not be the determining factor for initial provision of high cost person access chambers. Access for rehabilitation, as and when it becomes necessary, can be provided through an open cut pit, or technology may have improved for procedures to occur through the smaller chambers.

Hepworth International has developed a modular inspection/maintenance polypropylene chamber of 447mm internal diameter to cater for this market. These chambers are light, easy to handle and construct, have a benched, multiple entry base, are watertight and can be constructed to any depth with light or heavy lids. They have a considerable cost advantage over conventional concrete chambers. The pits are specifically designed for use with Hepworth SuperSleve pipes and are more than competitive with existing plastic chambers. The use of these inspection chambers with Hepworth SuperSleve clay pipes will provide Authorities significant savings in initial costs for sewerage schemes.

CONCLUSION

Hepworth International produces a calsined clay pipe system which is world’s best practice.

Hepworth SuperSleve calsined clay pipe system offers the specifier, user and asset owner an economic alternative with long term benefits over conventional clay and plastic pipes. It addresses the major concerns of root intrusion and infiltration/leakage.

Hepworth can offer innovative solutions to meet the market’s specific requirements in a cost effective manner.