The New Zealand standard for systematic CCTV condition assessment of gravity sewer and stormwater pipelines.

The NZPIM 4th Edition defect code system is the foundation of every pipe inspection report. Each observation recorded during a CCTV survey is assigned a single-letter or two-letter main code that identifies the defect category. The standard divides observations into three groups: Structural Defects, Service Defects, and Construction Features. Structural defects directly affect the physical integrity of the pipe wall and include Crack (C), Broken (B), Deformed (D), Joint Defect (J), Surface Damage (S), and Tomo/Void (T). The Tomo/Void code is unique to NZPIM and captures pipe wall loss or visible voids behind the pipe that indicate ground erosion or external damage not typically coded in other standards.

Service defects impair the hydraulic performance of the pipeline without necessarily compromising structural integrity. These include Roots (R), Deposits Attached (DA), Infiltration (I), and Obstruction (O). Root intrusion is the most common service defect in New Zealand's sewer networks, where mature tree roots penetrate joints and cracks to access nutrient-rich wastewater. Deposits Attached (DA) covers encrustation, grease buildup, and mineral deposits adhering to the pipe wall that reduce effective cross-sectional area. Construction Features such as Lateral (L) and Manhole (MH) are non-defect observations that record the location and condition of connecting infrastructure. General Comment (GC) provides a free-text entry for observations that do not fit the standard code categories.

This separation of structural and service codes is critical because NZPIM calculates two independent grades for each inspected pipe section: a Structural Condition Grade and a Service Condition Grade. A pipe may have excellent structural integrity but severe root intrusion, or vice versa. By maintaining two parallel grading streams, asset managers can prioritise structural rehabilitation separately from operational maintenance, targeting budgets more effectively. For comparable European sewer defect coding, see the EN 13508-2 standard.

The NZPIM 4th Edition Condition Grading system assigns each inspected pipe section a score from 1 to 5, where Grade 1 represents Very Good (as-new condition with no defects) and Grade 5 represents Very Poor (the pipe has failed or failure is imminent). Critically, NZPIM calculates two independent grades: a Structural Condition Grade based on codes C, B, D, J, S, and T, and a Service Condition Grade based on codes R, DA, I, and O. Grade 2 (Good) indicates minor deterioration such as superficial surface wear or minor staining, with no structural risk or flow restriction. Grade 3 (Moderate) marks the threshold where defects become distinct and require monitoring, such as medium fractures, displaced joints, or root intrusion blocking less than 25% of the cross-section.

Grade 4 (Poor) signals significant defects that demand rehabilitation or repair in the near term: large cracks, deformation exceeding 10% of the pipe diameter, or broken pipe sections with visible soil. Grade 5 (Very Poor / Failed) is reserved for collapsed pipes, total blockages, extensive corrosion through the full pipe wall, or deformation so severe that the pipe can no longer convey flow. The dual-grade approach ensures that a pipe with minor structural cracking but severe root blockage receives a low service grade despite its adequate structural rating. Asset managers use the worse of the two grades to prioritise capital renewal, while the individual grades inform whether the intervention should be structural (relining, replacement) or operational (root cutting, cleaning). New Zealand councils typically integrate these grades into their long-term infrastructure strategies, feeding condition data into predictive deterioration models.

The condition grading methodology is published by Water New Zealand.

What distinguishes NZPIM from simpler inspection checklists is its distance-based linear observation log. Rather than providing a single overall assessment, the inspector records each defect at its exact position measured in metres from the upstream start node. This creates a longitudinal profile of the pipe's condition that asset managers can use not only for grading but also for targeted rehabilitation design. A rehabilitation engineer can specify that relining is needed from 12.5 m to 18.3 m where multiple cracks cluster, rather than relining the entire pipe section at far greater cost.

Each observation entry consists of a distance measurement, a main defect code, an optional characterisation, an optional quantification, clock-face position references, a photo capture, and free-text remarks. The distance field must increase monotonically: entries are ordered sequentially from 0.0 metres at the start node to the total pipe length at the finish node. NZPIM also supports continuous defects, where a start and finish distance bracket a defect that spans a measurable length. A longitudinal crack running from 4.2 m to 9.8 m would be logged with a continuous flag rather than as a single point observation.

The clock-face position system records where on the pipe circumference a defect is located, using a 1-to-12 numbering system analogous to a clock face when viewed from the upstream end. Position 12 is the crown (top), Position 6 is the invert (bottom), and positions 3 and 9 are the springlines (sides). Recording both a "from" and "to" position captures the circumferential extent of a defect. A crack spanning from position 10 to position 2 passes over the crown, while a crack from 4 to 8 runs along the lower half of the pipe. This positional data is essential for rehabilitation design, particularly for patch repairs and targeted structural interventions where knowing the exact location and extent of damage determines the repair method and cost.

For a complementary manhole inspection methodology used alongside pipe surveys, see the NASSCO MACP manhole standard.

NZPIM's characterisation codes provide the second level of detail for each observation. While the main code identifies what type of defect is present, the characterisation describes how it manifests. For Crack (C) defects, the characterisation distinguishes between Longitudinal, Circumferential, Multiple, and Spiral patterns. A longitudinal crack runs along the length of the pipe and typically indicates beam loading or differential settlement, while a circumferential crack encircles the pipe and often results from shear forces at rigid connections. Multiple cracks in a localised area signal advanced structural deterioration that may soon progress to a Broken (B) condition.

Joint defects (J) are characterised as Open (gap visible between pipe segments), Displaced (angular or lateral offset between segments), or Faulty Sealing Ring (seal material visible or protruding). Root observations (R) distinguish between Fine Roots (individual filaments), Mass Roots (dense mat of root material), and Tap Root (single large root penetration). Surface Damage (S) is characterised as Wear/Erosion, Corrosion/Chemical Attack, or Spalling, each pointing to different deterioration mechanisms and material vulnerabilities.

The quantification field measures the severity or magnitude of the observed defect. For cracks, the inspector selects Small/Hairline, Medium, or Large based on visible crack width. For deformation, the quantification records the percentage of cross-sectional loss: 0-5%, 5-10%, 10-25%, or greater than 25%. Root and deposit observations use percentage of cross-section blocked to indicate flow restriction severity. This quantification data directly influences the Condition Grade calculation: a small hairline crack contributes less to the structural grade than a large crack with visible displacement, even though both carry the same main code of C. In the form, these three fields (main code, characterisation, quantification) work together to produce a complete, standardised description of each defect that any qualified inspector worldwide can interpret consistently.

For a comparable North American sewer coding approach, see the NASSCO PACP sewer standard.

The NZPIM inspection header establishes the context for every observation that follows. Start Node ID and Finish Node ID identify the manhole or access point references at each end of the pipe section, linking the inspection to the council's GIS asset register. The Direction of Survey (Upstream or Downstream) determines how distance measurements are interpreted and ensures that multiple inspections of the same pipe section can be compared regardless of camera deployment direction. Pipe Material is a required field with options including Asbestos Cement (AC), Cast Iron (CI), Concrete General (CONC), Reinforced Concrete (RC), Earthenware/Clay (EW), Polyvinyl Chloride (PVC), and Polyethylene (PE). The material code is critical because expected defect patterns vary significantly by material. AC pipes are susceptible to longitudinal cracking, EW pipes commonly exhibit joint displacement, and PVC pipes are prone to deformation under external loading.

Pipe Shape (Circular, Egg Shaped, Oval, or Rectangular/Box) and Height/Diameter in millimetres describe the physical geometry. Non-circular shapes require additional width measurements. The Inspection Method field records the technology used: CCTV (TV), Pan-Tilt CCTV (TVPT), Fixed Zoom (FZ), or Photographic (P). Pan-tilt cameras provide superior lateral and circumferential coverage compared to fixed-axial systems, and the method code allows report reviewers to assess the reliability and completeness of the observation data.

Environmental context fields include Weather Conditions (Dry, Rain, Heavy Rain, or Showers), Purpose of Inspection (Maintenance, Handover/Acceptance, Rehabilitation Design, Infiltration Investigation, or Operational Issue), and Pre-Cleaning Status (No Cleaning, Light Cleaning, Heavy Cleaning, or Jetting). The purpose field drives the level of detail expected: a handover inspection for new pipe requires documentation of every minor construction feature, while a maintenance survey focuses primarily on deterioration and blockage. Pre-cleaning status is essential for interpreting the observation log because debris or deposits visible during an uncleaned inspection may mask underlying structural defects. For a comparable approach to pipe inspection documentation used widely in the UK, see the WRC MSCC5 sewer standard.

NZPIM is maintained by Water New Zealand and aligns with the ISO/TR 11295 framework for condition classification of drainage systems.