For some time the topic of the useful life for repair procedures has been a matter of controversial discussion. In the process, giving across-the-board indications of useful life for 'repair procedures' has increasingly come to be seen as indefensible. Even when, in addition, a separate approach for different groups of repair procedures - 'robot procedures' for example - is suggested, this kind of generalisation is still not satisfactory. Previous experience with different robot systems suggests the conclusion that a more in-depth qualification is required.
Long-term experience with the various robot procedures is very different, however, depending on the procedures and the materials used. A qualified consideration of different procedures therefore leads to different predictions of useful life.
In this, the robot procedures are to be considered both as independent repair procedures as well, increasingly, as supplementary procedures for a renovation with the pipe liner. Especially in the latter cases, a qualified statement about the useful life is important in order to be able to make reliable statements about the overall useful life of the 'entire' renovation with the pipe liner.
Until now a determination of useful life has basically been a prediction based on a qualified assessment of the procedure and the materials used. In the past this was the only option, as there was no real long-term experience over extended periods. But now this long-term experience does exist for some procedures. This offers the possibility of comparing the predictions with real experience.
Long-Term Experience From Göttingen And Schwerte
In this article a comparison like this will be considered for the KATE procedures. For this purpose long-term experience from the cities of Göttingen and Schwerte will be presented. This experience will be assessed in the context of the preceding theoretical consideration.
Generally, a long useful life can only be achieved through a controllably high quality level. Furthermore, all renovation work must satisfy the requirement for optimal cost-effectiveness. In principle, the procedures differ from one another in the following main characteristics
- Process engineering
- Material used
The KATE procedure is distinguished by clear procedural control. Such a clearly specified procedure means that sources of error are excluded to the maximum extent possible.
The material used is a qualified epoxy resin that, because of the procedural requirements, can be 'cold' hardened by the specific decoupling of the formwork for the KATE procedure. This also reduces sources of error, which are significantly higher in heat-supported hardenings or when fast-hardening materials are used. Thus the prerequisites for predicting a longer useful life exist. So now the question of what long-term experience / market penetration there is for the procedure is of interest.
Long-term experience is extremely helpful in determining the reliability of a procedure. In this consideration, the market penetration of the procedure plays an additional role, as the amount of experience - the statistical raw material so to speak - is larger and thus more meaningful. An example should demonstrate that:
Experience values from more than 20 years now exist for the KA-TE procedure. If the average fleet size (market penetration) and the - verifiable - resin consumption of this fleet are taken into account, the result is that with this procedure alone 40,000 to 50,000 repairs have been carried out annually in the last ten years, that is a total of approx. 400,000 to 500,000 repairs, without serious faults having been noted. Conclusions and experience of this type say more about quality and useful life than predictions and estimates.
It was possible to determine comparable experience values for other procedures, in which the values for long-term experience and market penetration are lower with the other procedures, and for some procedures the assessment of freedom from faults is not as positive. The following experience reports from Göttingen and Schwerte confirm this fundamental 'statistical' experience.
Experience Report From The City Of Göttingen(GEB)
Göttingen can now look back on more than 20 years' experience of sewer renovation and is pursuing the objective of having demonstrably 'leakproof' sewers by 2035. According to DWA leaflet M 143-14 (Sewer renovation strategies), the Göttingen Disposal Company (GEB) listed all renovation procedures used since 1993 and subjected them all to a comprehensive quality inspection. As a certified company, the GEB consistently uses only procedures that guarantee long-term renovation success.