A CCTV inspection provides information about the condition of a pipe through the eyes of the camera lens; a 2D view of the inside pipe surface above the water level. This technology is perhaps the best inspection system available because of the breadth of information that it can provide, wide availability, cost-effective use and easy-to-understand output.

A CCTV investigation provides multiple levels of inspection including identifying the general information and conditions of the pipelines investigated as well as prioritising pipes for further rehab investigation. On a second level, the product can focus on the defects and features of specific lines for an appropriate rehabilitation design for each pipe.

Identifying pipe information

CCTV inspection is a very good means of identifying information about the pipe system. This information can be used for planning a rehabilitation project by helping utilities better understand their system and to determine the general condition of the pipes inspected, and enabling the works to be prioritised.

Figure 2 provides an example of the information captured on a CCTV log sheet. This information identifies the pipe and its attributes, and can be used to update utilities’ GIS and asset management databases. This data includes:

• Connectivity; identification of the upstream and downstream manholes
• Location; identification of the position of the nodes
• Laterals; identification and confirmation that the status – live or dead – of the laterals and their connectivity
• Length; confirmation of the length of the pipe
• Material; confirmation of the pipe material
• Diameter; confirmation of the pipe diameter

Most CCTV data management software systems will automatically calculate the grading of the pipe from the observations recorded. This is designed to provide an assessment of the overall condition of the assets in the system, as well as a trigger to indicate possible problem areas for further intensive study. In addition, it allows an indication of any changes in condition from previous inspections.

Identifying defects

CCTV can also be utilised as a more focused rehabilitation planning tool by identifying and qualifying the defects and service problems in each pipeline to produce specific rehabilitation designs. To obtain quality information, certain issues need to be considered.

The first pertains to the level of skill required for the camera operator, as CCTV relies on the skill of the camera operator for both recoding observations and capturing an image of the pipe that allows suitable diagnosis of any defects.

The second refers to different materials presenting different types of defects. It is important to consider the type of problems that could be expected and whether additional inspection methods are needed to complete the investigation.

CCTV versatility

CCTV inspections cannot prove that a pipe does not leak if there is no evidence of leakage available, however at the North Shore City Council in Auckland New Zealand, CCTV is being used to identify leaky private laterals.

The council was hydrostatically testing private wastewater service connections to identify pipes that allowed leakage into the system, but the testing posed a few problems. The testing was expensive to undertake and could only test the service connection up to the lowest gully trap. Furthermore, property owners found the test results hard to understand and were not sure which sections of pipe required repair.

The council therefore decided to rely solely on CCTV inspections for determining whether pipes were acceptable or not. A grading system was developed by adjusting the standard condition rating scores – from the New Zealand Pipe Inspection Manual – for each defect code to reflect the impact it had on the leakiness of the pipe. Applying scoring analysis, property owners were required to repair drains with peak scores above 15 or a mean scores above 0.5. Trialling this system found that it gave similar results to hydrostatic testing.

Limitations of CCTV

A CCTV image provides qualitative information on the pipe condition, but not quantitative information. Therefore, the technology has some limitations as to what information it can provide that is necessary before conducting an investigation.

For example, CCTV technology cannot provide information beyond the inside surface of the pipe being inspected – it cannot provide information on the condition or thickness of the pipe wall material, nor can it determine whether there are cavities behind the pipe wall – unless it is visible through an opening in the pipe wall. In addition, the product cannot measure the dimensions of a defect or pipe attribute or accurately determine any loss or deformation of the pipe surface.

In short, CCTV inspections rely on being able to clearly see the pipe and the presence of ‘evidence’ – such as displacements, roots or infiltration – to determine the severity of most observations.

Developments to overcome limitations and improve diagnosis

Since the introduction of pan and tilt cameras, there has been some significant developments of camera and software technology that extend the capabilities of CCTV inspections.

The development of the digital CCTV camera has made significant improvements to the quality and amount of information available through digitising the images and allowing the measurement of defects and intelligent analysis capabilities. Certainly, digital camera technology is the way of the future and eventually will leave analogue video to disappear the way of VHS tapes.

Pipe wall loss or the deformation of a pipe can be identified by CCTV, but the visual evidence generally needs to be pronounced for it to be seen. Deformations in non-flexible pipe are usually easy to see due to characteristic longitudinal cracking, however quantifying the severity of wall loss or pipe deformation in flexible pipes is very difficult. Increasingly, laser profiling equipment is being utilised in conjunction with CCTV inspections, giving a third dimension to CCTV images.

Similar to the laser profiling equipment, sonar technology is also becoming a more common tool in applications where flow within a pipeline is significant and an image below the water surface is needed.

Measurement of pipe defects

The IPEK Supervision camera provides an advancement more commonly available and at a similar cost to a standard CCTV inspection. Whereas picture distortion and magnification on a standard CCTV image makes measurement of pipe defects entirely inaccurate, the supervision camera operates with the addition of two inbuilt lasers that project straight beams of light onto the pipe surface. The beams are positioned 45 mm apart, providing reference distance within the video picture that can be used to calibrate measurement equipment.

When analysed with the Cleanflow Laser profiling software – the same software used for profiling – it is possible to reliably measure to accuracy of up to 0.1 mm sensitivity; enough to easily measure crack widths. Open joints are possible to be measured off the screen with a scale rule. See page 44 for further information.

CCTV is the most versatile inspection method available for rehabilitation investigations. New technology is becoming more readily available that either will enhance the information that we can get from CCTV, or in the near future improve its capabilities to overcome a number of current limitations.

Consideration needs to be given to ensure operators and engineers are suitably skilled to capture and interpret the information gathered. The limitations of CCTV inspections must also be understood so that additional investigations may be undertaken in order to provide quality information for the rehabilitation program.