Substance classification: deciding which pipe comes first
Why condition class leaves the question open
Condition class is an extreme value: it reflects the single worst observation in a pipe section. That makes it right for spotting acute risk, and insufficient for planning investment.
A utility looking at three hundred sections all rated the same condition class has no basis in that number for deciding where to start. A sharp single defect and widespread wear across thirty metres can carry the same condition class while leaving entirely different amounts of usable substance behind.
Substance is a balance, not an extreme
Substance classification expresses how much wear reserve a pipe section still holds, measured across its whole length rather than at its worst point. Condition class answers how bad it is right now. Substance class answers how much is left and what kind of measure the section warrants. The two are complementary, you need both.
The six substance classes
Substance equals one minus wear, so the number reflects what is left: class 5 is the best state, class 0 the worst. The right-hand column describes tendencies rather than a fixed rule, the class narrows the range of sensible measures, it does not select one.
How wear is calculated
Wear is derived from the coded observations themselves. Each observation contributes a damage length, weighted by the geometry of the damage and by the severity class assigned to it, and the total is set against the length of the inspected section.
Severity here refers to the class of each individual observation, assessed separately for watertightness, structural stability and operational safety, with the most critical of the three governing. This is a different thing from the condition class of the whole section, even though both use a nought-to-five scale.
Identical damage overlapping at the same point is condensed rather than counted twice; different damage categories at the same location contribute separately. Normalising against section length is what makes the result comparable across sections of different length and diameter.
What the calculation needs
The calculation runs on the coded inspection data itself: the position of each observation, its code to DIN EN 13508-2 including characterisation, whether it is a longitudinal damage, its severity class to DWA-M 149-3, its damage length, and the inspected length of the section. Material, age and diameter are not inputs to the substance figure — they come into play later, when the measure is chosen.
Scope
Substance classification in Pallon covers mainline sewers, on inspection data coded to DWA, VSA or ISYBAU. Manholes, laterals and NASSCO-coded data are not currently covered.
The method was developed in the SubKanS research project as a transparent, practice-oriented procedure, built by analogy to condition classification so that it fits established workflows.
Substance classification and rehabilitation planning
The two are related but distinct. Substance classification produces one figure: how much wear reserve a section holds. Rehabilitation planning uses that figure as one input among several, alongside defect types and counts, condition class, boundary conditions and your own cost catalogue, to propose measures and compare plans.
What this requires from the coding
Substance classification is only as good as the coding underneath it. Where observations are summarised into groups or minor severities are left out, the calculated substance shifts. This is the practical reason complete and consistent coding matters beyond compliance: it is the input every downstream planning figure depends on.
Pallon codes each observation individually and quantifies area and severity from the image-based 3D reconstruction of the pipe, which is what makes a substance figure comparable between two inspections ten years apart.
Frequently asked questions
Does the substance class decide the rehabilitation method?
No. The class narrows the range of sensible measures — higher classes point towards repair, lower ones towards capital work — but it does not select one. The actual choice draws on defect types, condition class, boundary conditions and your own cost catalogue, and the engineer decides.
Does Pallon calculate substance class for manholes?
Not currently. Substance classification covers mainline sewers, on inspection data coded to DWA, VSA or ISYBAU. Manholes, laterals and NASSCO-coded data are not covered.
Is substance class 0 good or bad?
Class 0 is the worst state – the substance is fully consumed. Class 5 is the best. Substance equals one minus wear, so the number reflects how much is left rather than how much damage there is.
What is the difference between condition class and substance class?
Condition class is an extreme value – it reflects the single worst observation in a pipe section. Substance class is a balance across the whole section, expressing how much wear reserve is left. Two sections with the same condition class can hold very different amounts of substance. Both use a nought-to-five scale, which is why they are easily confused.
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