Balancing Hitting Your Mark and Minimizing Wrinkles In Liners

For those of you new to this blog, you can find all of the previous blogs regarding the CIPP lateral lining industry at if you would like to browse and read any that have an interest to you. We also have a certification training session at the Springfield, MO office, Friday, April 21, 2017. Call 417-719-7172 for details.

Wrinkled Liner

Many of you get tugged between having a lateral liner look “perfect” around corners while expecting to hit a mark within a +-2″ ending location. This isn’t something new and before continuing let’s eliminate under cured liners that have buckled from pulling the calibration tube too early. We’re talking about wrinkles caused by excess liner material that bunches around a turn on the inside of the turn. We’re also talking about using liners that expand  to transition from one dimension to another (4″ to 6″).  The materials used in the areas that you are addressing turns and size transition is usually stretchy and often referred to as a high loft product with more space between the fibers than you’ll find in the higher density materials that are stiffer.

Scrim Liner

So let’s look at the most widely used material, the material that minimizes stretch and is used when wanting to “hit a mark” in the sewer line. As we’ve discussed this material tends to bunch in turns. To minimize the bunching appearance, we’ve instructed users to follow these guidelines: After insertion of the calibration tube, and before setting the curing pressure, raise the pressure to 30 psi for approximately 30 seconds. This procedure will stretch the material to fill in any voids between the material and host pipe, and will flatten out some of the excess materials. After this procedure, reduce the cure pressure to 5 to 8 psi and finish curing the liner with ambient air temperature/pressu, hot water or steam. While this will not eliminate all of the wrinkling, it will give you the best appearance you can expect with this material. Educating your customer may be the simplest way to “sell” the appearance as the wrinkling on the inside of the turn doesn’t impede the flow in the line and isn’t an area that catches solids.

Stretchy Liner

If wrinkling around a corner is unacceptable, you may want to look at stretchy liners. The softer higher loft materials that tend to be stretchy are a different story from the high density materials described above. We can expect both stretch and shrinkage with this material. If using a  4.5″ to 5″ diameter material inside a 4″ pipe that transitions to 6″ pipe, the 4″ material will elongate, and will shrink as it expands into the 6″ material. We’ve tried to quantify this with a stretch calculator, but the variables can make the outcome still unpredictable. More pressure causes more stretch and expanding the material to fit the larger dimension causes it to shrink. Ambient temperature of materials affect the stretch factor. Turns modifies the landing spot as well as which stretchy material you choose to use. It’s still a good practice to increase pressure to 30 psi for approximately 30 seconds to push out any wrinkles left from the inversion or pull in place process and to expand the liner to the voids between the host pipe and the lining material. You will be tasked to either add a point repair to fill in a short landing or employ a cutter to lop off a liner that goes long.

Welded Hybrid Liner – Stretchy & Non-Stretchy

So here’s a new approach that I’ve tried and it works but requires some preparation to help you execute it correctly. You will need to know the location of each turn and the area where the liner transitions in size, if any. Knowing that the higher density material can hit a mark within a margin of error, we will plan the majority of the install with this material. Plotting where the turns and transitions are, we can cut a section of stretchy material to make the turn or transition. By minimizing the length of liner we’re using for those areas to a couple of feet of material at each turn or transition, we can predict where our liner will end a little easier. In other words, when you only have a few feet of stretchy material to deal with, stretch won’t fluctuate as wildly as it would in a 100′ shot that may leave you to deal with 10′ +- of where you want to end. If I’m dealing with 4′ of material and I’m guessing a 10% stretch factor for that material, I’ve only got a few inches to deal with as far as stretch and can predict where my liner will end with a high degree of confidence. This process uses our TPU material to weld high density liner to the stretch material where it’s needed and back to high density liner.

So there you have it. 3 different approaches to lining your lateral job. As will each choice, planning will ensure your success. If you have questions, call us for more details.