Can You Salvage A Liner That “Sags”?

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Buckled Liner

“I shot a 268′ liner and it sagged. After reading your explanation of why it occurred, I think I understand the buckling issue. Yes, we had rain a few days before I lined the pipe and there was ground water coming into the pipe I lined, but assumed that the water would be about the same temperature as the ground. Anyway, is there any chance I can “round out” the liner and if so, how?”

Before we address the “rounding out”, let’s discuss the reason you got the sag. Understanding why it sagged may help you prevent future sags. Rain falling from the sky starts out as ice in the upper atmosphere. As it falls it heats up and by the time it melts and hits the ground may see ambient temperatures in the upper 30s to mid 40s or 10 to 15 degrees colder than the ground. This water, as it infiltrates, cools the surrounding ground. If that cooling is near a line you’ve just lined, you may see a colder temperature of the ground thus it cures at a much slower rate. If the rest of the liner achieves a cure state above the buckling point, you are good to go for those sections, but, if a section of liner is below the cure point needed to stand alone, you can experience buckling. This buckling can cause a sag, a shark fin, or other state that shows something is wrong with the lined pipe.


Now that we’ve identified what caused the sag, what are our options? We have three options available to us and I’ll run through them in the order you may want to try them. The first option is an attempt to “round out” the sag by inserting a calibration tube, heating the liner to a temperature above the point that the liner is cured to and hold it there for a period of time until it is fully rounded out to the wall of the host pipe. Each resin has a different heat deflection temperature (HDT) after it has been fully cured. This is the temperature that the liner will soften. But before it is fully cured, the HDT is less than the advertised meaning that the liner will deflect before the published temperature and depending on that state of cure, the temperature may be substantially less. If your resin advertised HDT is 197F, then any temperature you achieve in excess of that number means you may be able to remold it to a condition that fits the host pipe. If your HDT is 250F, and the liner has achieved a fully cured state, it would take a temperature of 250F+ to round out the liner. As I indicated, this would be my first approach to fixing a sag, and the sooner after you discover the sag and attempt this repair the better your chances of success. Just remember that this will require you to slowly cool down the reformed liner so you don’t stress crack it with cold water after you’ve finished rounding it out. The older the liner, the more curing it’s achieved, so timing is important here.

The next approach would be to remove the sagged portion of the liner. You can employ wire brushes, sandpaper, or carbide cutting tools to mill out the portion of the liner that has sagged. Once this has been completed, a point repair patch of liner and resin may be inserted to cover the removed portion of liner. This a pretty straight forward repair you can complete with a TPU leader welded on to a section of liner tube, wetted out, and inverted into place followed with a regular calibration tube to cure it. Or you could wrap the section of liner tube turned inside out over a pipe packer, wet it out and pull or push it into place. Fiberglass may be used in place of scrap liner tube for this application.

Excavator Removal Tool

The final approach is to dig it up. When all else fails an excavator may be your only option, although this option is used more than needed due to panic. I can’t tell you how many times the excavator was brought in because of panic and ended up costing everyone more money.

So there you go. You have 3 ways to solve an issue that you may encounter in your lining experiences. Hopefully learning why these occur can help you make sure your liner is cured enough before you pull your calibration tube. 15 minutes of added cure time may save you days of fixing the result of a sag in the liner.

Friday, April 21, 2017 at the Training Facility in Springfield, MO is another CIPP certification training for installers who want or need to be certified by the sewer agencies where they work. Please call our office to see if they can still fit you in. 817-719-7172. 

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