A closer look at the history of conduit coding and the importance of correct coding in
delivering accurate CCTV inspection reports.
The interpretation of photographic and CCTV conduit inspections in Australia started in 1965, when film cameras came onto the market, first using black and white then colour film.
Picture quality was good due to plenty of light sourced from a high lumen xenon flash light and high resolution film, and the picture was captured at the camera head rather than having to send the signal up through a cable to the camera truck.
The disadvantage with film was that after the inspection the film had to be processed and then calibrated to show a longitudinal reference point (LRP).
CCTV was introduced sometime in 1974 when the Melbourne Metropolitan Board of Works purchased an IBAK forward viewing CCTV camera mounted on skids, with a very heavy 35 mm diameter cable.
Hand winches were mounted on the upstream and downstream manholes, the camera was winched through, and anything of interest was photographed off the screen.
The best part of this practice was the fact that the problem could be identified straight away. Unfortunately it was slow and due to the poor resolution available at the time it was very easy to miss a defect.
Surveys of newly constructed reticulation areas were introduced as a requirement before handover to sewer and stormwater authorities, which greatly improved the standard of construction.
CCTV was responsible for discovering inadequacies in polyvinyl chloride (PVC) when it was introduced as an alternative pipe material for sewers.
A change in construction techniques and an increase in the wall thickness of PVC was required to avoid deformation.
Since then a properly constructed PVC pipe has proven to be a successful material for use in sewerage and drainage construction.
Sewer maintenance
Early camera and CCTV inspections were commonly used as a post-inspection tool after an event, like a blockage or collapse.
These inspections revealed that there were some types of pipe, mainly concrete of a certain age and make, that were deteriorating very quickly and required urgent attention.
Repair budgets were small and repair methods were limited to various methods of sliplining using PVC and a short polyethylene liner that could be installed from a manhole.
Monier and Humes would later introduce a cured-in-place pipe (CIPP) fiberglass full length type-liner.
Preventative maintenance CCTV programs were established and it quickly became apparent that most of the areas inspected needed urgent repair or replacement.
Operators were tasked with grading the pipe repairs from ‘urgent’ (which would require immediate replacement), to ‘not too bad’ which would require action in at least a couple of years.
In order to create a level of consistency in these determinations CCTV inspectors began to deliver hand-written reports on condition assessments.
Reports sheets were made up with space for header information and an histogram for a score at every meter between 1-10.
A dot was marked on the histogram in line with the LRP and the score given to the structural defect in concrete and also a score for a service defect that included roots, grease, obstructions, infiltration etc.
At the end of the survey the dots were joined and a peak and average score for that conduit length could be calculated.
If there was only one bad peak score the pipe was put on a dig out or point repair list, extending its service life.
Pipes with a high average score and many high peak scores were put on the ‘urgent’ list for full relining or replacement, the rest were given a grade for re-inspection in 2-15 years and beyond.
The ‘urgent’ list for immediate replacement was always the biggest, but it was an efficient way of spreading the available rehabilitation budget.
The reports were labour intensive, portable personal computers were only just starting to appear on the market and they were very expensive and not very reliable.
It wasn’t until around 1986 that the reports, including the histogram, were successfully produced on computers.
By this time more CCTV contractors were appearing on the scene and this was good for production but not so good for the consistency of the reports.
Operators all appeared to have a different way of describing or coding a defect and differences in the final grade of the inspected length were common. It became apparent that training was required to maintain consistency of coding.
Consistent reporting
After meeting with other major authorities in 1988, Sydney Water embarked on a similar CCTV inspection program, which tackled the coding inconsistency in a different way by bringing out a software coding package called Sewrat.
Large CCTV contracts were advertised and the contract specified that all operators were required to attend a two-day certificate course based on the Sewrat manual that contained defect codes, defect descriptions and pictures, scores, maximum speeds through the pipe, and header information. This subsequently improved the quality of the reports.
The program was similar to the European WRC codes, the computer program at the end of a survey would calculate a peak and mean score and grade the pipe from one to five.
Today the CCTV industry uses the WSA versions of the conduit condition codes after the Water Services Association of Australia (WSAA) decided the industry needed an official national based coding system that covered sewer and storm water more effectively, with a greater choice of codes and descriptions.
The latest edition, WSA 05-2013 manual has been released but, until now, a software package to run this edition has not been not available due to a number of discrepancies in the coding and scores.
Auscodes, in collaboration with PipeTech, will be introducing a WSA-05 2013 version in September.
Discrepancies in the code and scores have been addressed and on acceptance by the industry will be forwarded to WSAA for amendments to the manual.
For more information visit the Auscodes website.
Part two of this article will be published in the December edition of Trenchless Australasia and will cover guidelines for delivering useful and accurate CCTV reports.
This article was featured in the September edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet, or mobile device, click here.