Pitch fibre pipes were first laid in the 1950’s as a cheap alternative to clay pipes and over the last few years have been the cause of many blockages. This is generally due to the fact that they were designed and installed in the same way as clay and concrete pipes. It became apparent that pitch fibre pipes required a higher degree of soil / back-fill compaction which subsequently led to a new philosophy (Flexible Pipe Design and Installation). By 1967/68 other publications had begun to recommend that flexible pipes, including pitch fibre, should be laid with a granular bed and surround. These included in 1967, DoE Advisory Leaflet 66 – Laying Flexible Drain and Sewage Pipes, and in 1968, CP20059: Sewerage. The use of a granular bed and surround was not included in BS 27604 until it was revised in 1973.
BS 2760 was withdrawn in August 1987. The reason the Standard was withdrawn is not known but the most likely explanation is that the pipe had not been manufactured in the UK since 1984.
Over the years the majority of serviceability failures arising from excessive deformation of pitch fibre pipes occur as a result of poor installation, either due to inappropriate and inadequately compacted surround material or through the use of bricks or other hard objects to set the line of the pipe.
The service life of pitch fibre pipe is generally assumed to be 40 years or less. However, the apparent number of failures, although significant, should be considered in the context of the large quantities of the pipe that were installed during the 1950s and 1960s. The apparent failure rate indicates that many pitch fibre pipes are likely to be serviceable for longer than 40 years.
Where the level of pitch fibre deformation is found to be 20% or less then it can be re-rounded and lined using a cured-in-place pipe (CIPP). This is because the CIPP has a greater ring stiffness than the pitch fibre pipe and therefore gives added support to resist deformation and other common problems. The same linings are used to renovate clay and concrete pipes within the water industry around the world and are designed and tested to last for 50 years providing a long lasting solution to a pitch fibre drain problem.
All Dynorod CIPP linings comply with the basic requirements of:
- BS EN 13566-4:2002: Part 4: Plastic piping systems for the renovation of underground non-pressure drainage and sewerage networks – Lining with cured-in-place pipes.
- Water Industry Specification (WIS) 4-34-04: Specification for renovation of gravity sewers by lining with cured-in-place pipes: March 1995: Issue 2, published by the Water Research Centre (WRc Plc).
Each individual lining is designed, in accordance with the Sewerage Rehabilitation Manual (SRM), to withstand the long term effect of external hydrostatic pressures (i.e ground water) acting on the lining over a 50 year period.
If you need renovation work carried out on your Pitch Fibre pipes call Dynorod on 0845 026 0994 for a free quotation from the drains experts.
Dual Access (Manhole to Manhole)
In general, the patented No-Dig method used by Dyno-Rod to renovate pitch fibre pipes are as follows:
- A steel cable is introduced through the centre of the pitch fibre pipes.
- A steel reformer / cutter is then pulled through the pipe to remove any surface blistering or delamination.
- The steel reformer is then winched through the pipe several times so as to re-round the deformed sections of the pipeline.
- Finally, a polyester lining is pulled through the pipe, inverted and then cured in place restoring the pipeline back to its original shape.
Single Access (Manhole or Excavation)
In general, the patented No-Dig method used by Dyno-Rod is as follows:
- The re-rounding head is attached to both a steel rod and a winch cable.
- The head is then pushed through the pitch fibre pipe using the steel rods.
- The head may also be vibrated through a heavily deformed section (minimum diameter is 50mm) by attaching a kango drill to the end of the steel rod.
- The steel rod is rotated anti-clockwise to unlock the re-rounding head when located at the correct position.
- The re-rounding head is then winched back to the launch manhole re-rounding the pitch fibre pipe.
- The process may be repeated several times to re-round the deformed sections of pipe.
- Finally, a polyester lining is pulled through the pipe, inverted and then cured in place restoring the pipeline back to its original shape.
With respect to the rehabilitation of pitch fibre pipes other organisations are now offering similar services, some of which are in breach of the patent and as such are being contacted by the relevant authorities.
The first pitch fibre repair was carried out in Trivills Park, Liskeard, Cornwall in the spring of 1996 in conjunction with Royal Sun Alliance. Since 1996 Dyno-Rod has renovated over 150km of pitch fibre pipes and is now an accepted approach recognised by the environmental health people, in Cornwall, in restoring full flow conditions.
Where the deformation of the pitch fibre pipes has exceeded 20% under the requirements of the Drain Repair Book, published by WRc, it is not allowed to re-round and line the section using a CIPP. In these cases Dyno-Rod would use its in2 Pipe Replacement System.
Since this time a spokes person from Royal Sun Alliance has declared that “Pitch fibre pipe drainage problems have been increasing steadily over the past few years and are proving expensive to solve, but the insitu technique is offering us huge savings, sometimes more than 50% compared with standard excavations.â€
Call Dynorod on 0845 026 0994 for a free quotation from the drains experts.
