One of the largest concerns municipalities have when sliplining an existing pipe structure is if the liner pipe will fit inside the host pipe. There are a myriad of potential host pipe problems which determine liner pipe clearance: misaligned joints, out of roundness, protruding laterals, long radius curves, elbows, or pipeline breaks/deflections. These unforeseen complications can drastically slow down a project while a plan of action is formulated.
Situations like this are avoidable, primarily by improved planning early in the condition assessment phase.
Contech doesn’t perform condition assessments on existing pipelines, but we are frequently asked about required information necessary to determine if one of our solutions will fit. Below are three of the primary inspection methods used to determine pipe conditions: visual inspection, closed circuit television video, and laser profiling.
As I describe each option in more detail below, think through the required safety steps to take in each of these inspection operations. Always follow OSHA guidelines.
- Visual inspections are the most economical way to survey the condition of a pipe. For visual inspection to be a valid option, the pipe is typically 48” and larger, straight, and relatively short. Since most storm and sanitary sewers require confined space entry, visual inspection is mostly used for open ended culverts. The inspection is usually completed by municipality maintenance crews when the project is being designed and by the contractor to verify the measurements. Measurements are taken at pre-determined intervals and where the crew notices a condition which could create an issue with clearance. The purpose of the measurements is to determine the minimum inside dimension of the host pipe. From there, the maximum outside dimension of the liner pipe can be determined. With good measurements, determination of vertical and horizontal angles in the pipe can be made. Overall, culverts with multiple curves/angles, or closed end pipes should use a more exact form of inspection.
- Closed Circuit Television Video (CCTV) is used frequently for pipe inspection. A small cart outfitted with cameras traverses the pipe via remote operation. The inspection is typically completed by specialized contractors, although some municipalities have their own CCTV equipment and crews. Because of the required equipment and specialized crews, it is more expensive than visual inspections, but it also provides more information. Locations of existing conditions such as laterals, misaligned joints, pipeline deflections and alignment curves can be determined. While these trouble spots can be located, determining the degree of the trouble spot and exact dimensions can still be challenging.
- Laser profiling of existing pipe provides what I refer to as the “no doubt” fit. Like CCTV, a small cart is used to travel through the host pipe. In this case, the cart is outfitted with laser emitters which locates and measures all deflections, protrusions, elbows, etc. Special contractors perform the work, and it is more expensive than CCTV. But the payoff is enormous – plotting all the known points provides the designer and contractor with an exact model of the existing pipe. They can then model the liner pipe and make sure it fits through the host pipe long before liner material is purchased. The primary drawback of laser profiling is that the laser does not penetrate water, meaning invert information could be tricky to locate. To overcome that, try to laser profile in low flow conditions. Other contractors have used SONAR to see through the water in the pipe. While generally overkill for culverts, laser profiling is ideal for any pipe with multiple elbows, deflections, and other pinch points.
Determining which inspection method to use depends on factors such as pipe use, diameter, pipeline layout, existing conditions, and budget. From a pipe manufacturer’s perspective, the more information we have, the better off we will be.