Q: How many CIPP samples should be tested for a project?

A: The number of samples depends on the number of MH to MH sections. The inspector typically dictates when tests should be performed and authorizes payment directly by the owner. The contractor, by contract specified requirement, should provide a sample for every line section installed.


Q: Why is CIPP water inversion and curing considered to have a 50 year design life?

A: The long term life of a CIPP is predicted to be 50 years based on a documented installation about 40 years ago. Water is definitively the oldest curing technique, but more efficient methods such as steam and UV light have been developed and will achieve the same end result when executed properly. Regardless of the method, the achievement of a fully cured pipe is what is important.


Q: Are wrinkles/fins in CIPP a problem?

A: It depends on their location and configuration. Removal of wrinkles or fins is recommended when they exceed a certain height and are located in the invert and affect the flow characteristics of the pipe or can cause excessive flow backup or maintenance issues. Wrinkling is often the result of excess of liner material, for instance installing a 15 inch liner into a 12 inch pipe. Wrinkles in the radial (circumferential) direction are typically more critical than the ones in the longitudinal direction. Radial wrinkles affect the flow characteristics and may allow for debris build‐up in the pipe. Radial wrinkles located at the pipe invert generally create more issues than the ones located at the pipe crown.


Q: How are wrinkles/fins removed?

A: Wrinkles or fins can be readily removed on thin liners using a wire brush technique and on thicker liners using a cutting blade. If the wrinkles or fins have cured in a tight configuration causing the resin to be contiguous in the fin crosssection then removal of the fin should require no additional repair. If they have not cured in a tight configuration and the resin is not contiguous across the wrinkle, a short liner repair should be installed where the wrinkles or fins have been removed. If the repair is extensive the contractor may choose to install a thin liner into the entire section instead of multiple short liner repairs.


Q: Why do some publications require the CIPP liner to be cooled to 100 degrees Fahrenheit or lower after curing and before relieving the internal pressure?

A: The cool down temperature should be 100 degrees Fahrenheit or cooler whenever possible. A plastic, such as the CIPP liner, will continue to shrink as it cools down to sewer pipe ambient temperatures. The greater the temperature differential between the release of the pressure and the ambient sewer temperature, the more shrinkage will occur. It is generally understood that the cooler the temperature upon the release the tighter the fit of the finished product.


Q: What dictates the minimum liner thickness?

A: There are three criteria that dictate the thickness design of a CIPP liner:

1) Structural capabilities of the liner to withstand the design pressures imposed on it. The higher the physical properties, the thinner the product that will be capable of carrying the load.
2) Minimum thickness that is required for the liner to hold up against erosion and abrasion from the flow in the pipe over time.
3) Minimum thickness required to have sufficient strength to withstand installation forces, pressures and temperatures The greater of these three will dictate the thickness installed.


Q: How do I become a certified inspector?

A: You can attend any of a number of scheduled Inspector Training & Certification Programs offered by NASSCO. Simply check our website for a location near you. If there is no location near you, you can sponsor a training program in your area. Check the training schedule or email for details.


Q: Is it practical/possible to re‐line a lateral by accessing it from inside the building and terminating it at the mainline?

A: There are technologies available that can line a lateral from the building to the mainline. Recommended that you read "Overview of Lateral and Main/Lateral Connection Lining and Sealing Technologies" prepared by the NASSCO Lateral committee that reviews in detail all of the methods available in the industry for lateral rehabilitation.


Q: Can air testing be done on a 48 inch rehabilitated pipe?

A: Typically pipelines larger than 30 inches in diameter are not air tested but visually inspected due to the unsafe high pressure created while air testing a pipe of this size.


Q: How can I measure the CIPP resin volume in the field?

A: The resin volume can be confirmed during the wet‐out of the liner at the contractor's wet‐out facility. The alternative is to require that a certified wet‐out report be submitted by the contractor for each liner length to be installed for the project. The inspector can check the wet‐out report quantities against the contractor's submittals. A trained and certified NASSCO inspector will learn how to review all contract specified quality control requirements to ensure that the owner's expectations are achieved by the contractor.


Q: Should the specifications require a 400,000 psi resin or higher number than the usual 250,000 psi?

A: Resin strengths have improved significantly over the years. The 250,000 psi minimum flexural modulus has been in specifications since the beginning. If a higher strength minimum is specified, then the pipe will calculate out at a thinner thickness. In all cases, the resin manufacturer should be consulted to determine what resin strength is reasonably achievable in the field for their resin systems.


Q: Can a house connection address be added to a lateral liner for identification purposes?

A: Yes, there are some systems that will have the address printed on the inside of the mainline section so that it can be identified with a CCTV camera inspection.


Q: I am unfamiliar with CIPP end seals. What is their principle?

A: End sealing techniques have been used successfully for many years where the liner pipe enters the manhole. The seals are produced from hydrophilic rubber, which absorbs water and thereby swells to many times its original size, stopping water from entering the manhole from between the liner and the host pipe. This type of seal has been used to seal construction joints in a variety of applications including sewer pipe and manhole joints. There are a number of sources, including Hydrotite from Greanstreak Group Inc., and Insignia from LMK Industries, which has produced a product specifically for liner applications.