KEEPING UP with Lateral Reinstatement

Video inspection cameras are an important component when reinstating the lateral connections, assisting the air- or hydraulic-driven cutters.

Back in the 1970s — when pipe relining was in its infancy — one of the major questions that raised was: How do we re-open the laterals?
A Swedish liner system used short pipe sections, which were pushed into place from one side until the first lateral was reached. Next, the laterals were pre-measured and cut before the remaining sections were driven in from the other side. This was obviously cumbersome so the race was on to develop a remote-controlled cutter that could travel in a relined 8-in. pipe and had at least a 300-ft reach.

By the 1980s, the field had developed into either air- or hydraulic-driven cutters, assisted by standard sewer inspection cameras. Some of the issues in older sewer pipes were break-ins, or hammer taps and mineral deposits. Here, cutters with strong motors provided an option for removal by grinding or cutting to produce a pipe free of restrictions.

The next task was determining how to find the lateral in the relined pipe. Some of the liners would normally dimple outside the lateral but this could not be relied upon so attempts were made to place a locating device inside the lateral or use ultrasound or radar, but the way that survived was pre-measuring.
The two standard methods of pre-measuring were:

1) Dragging the cutter through the line prior to lining and marking the cable by the laterals

2) Making a separate line with markings. This second method allows for pre-measuring of several lines as part of the pre inspection.

Everyone who has cut laterals will agree that getting an exact measurement is time well spent. When the lateral is located in the relined pipe, the procedure starts by placing the cutting head in the center of the lateral and then backing up the camera 3 to 4 ft away while a hole is punched and the lateral is drained.

Next comes the actual cutting. Cutting heads comes in many variations, depending on liner materials and power of the cutting motor. I prefer large heads as these produce a cleaner edge without “shark teeth” that requires a second brushing. It further makes the “coupon problem” a non issue. Large heads grinds the liner material in such a way that bigger pieces don’t find their way to the lift stations.

In felt liners without a pre-liner bag, it can happen that resin is squeezed out of the felt and creates a resin slug in the lateral. Most common cutters, which move straight up and down, can only reach a couple of inches into the lateral and are unable to reach through the slug. Cutters that move up and down under an angle can reach further into the lateral and can, in most cases, alleviate this problem.

Another challenge is reopening the laterals where the lateral pipe is PVC. As opposed to clay or cast iron pipes in which sparks fly when you hit the wall, just a quarter-inch too far takes you straight through the wall in a PVC lateral.

To reduce this risk, heads have been developed with a ball bearing larger than the cutting edge and mounted on the top of the head. This requires a two-step cutting where a small hole close to the center of the opening is cut with a standard head to drain the lateral and give access for the second head, which is then following the edge of the opening.

The final item in the cutting scenario is the use of steel wire brushes to remove “shark teeth” around the edge of the cut. As these brushes make a water fog, they are dangerous when used in PVC laterals. In my work to repair holes through the pipe wall, I found that brushing was the most common culprit.

When it comes to development of more efficient cutters, European companies have approached the market in a more radical way than U.S. manufacturers. American-made cutters are all winched though the pipe and cut with relatively small air motors.

European cutters are in most cases self propelled and use a variety of cutting motors, which can be air-, hydraulic- or electric-driven. They further include built-in rotating cameras with lens cleaning devices and most have different movement options beyond the straight up and down, such as an elbow movement or even with a second movement like a wrist.

American-made cutters are all winched though the pipe and cut with relatively small air motors, such as a Bowman Dominator 4-30 cutter in 8-in. setup configuration with a 2.5 hp-geared air motor.

This means the requirements for operators and maintenance personnel for these cutters have changed from the standard crew member who will stand long days, not being afraid of getting dirty or being away from the family, to someone who is more of an electronic mechanic working in the field. Because of the general view in the American public that sewer workers stand in sewage to the waist, it is very difficult to attract people with sufficient education to operate in this field.

One more thing that is different between the United States and Europe is that by now more than half the liners in Europe are fiberglass with an outside foil. This ensures that the resin is contained and does not leak out in the lateral opening.

Felt liners, which are dominating in the United States, normally do not have outside foil. This may cause uncured resin to mix with water in the lateral to a “syrup.” This cannot be removed by the normal lens cleaning devices but requires a trip out of the line and cleaning with acetone The initial drain zone from the lateral is, therefore, not the most desired spot for your camera.

This brings us to the final chapter: What to do when there is a hole out in the ground either caused by the cutting action or caused by an old “break in” that has lost contact with the main line?

Earlier, the answer was always: dig a hole. Today, the problem can, in most cases, be corrected by bringing in lateral sealing equipment that places a hat profile in the lateral opening. This equipment uses a felt or fiberglass material impregnated with a polyester or epoxy resin and cured ambient or with heat or UV light. During the curing, the soft hat is held in place by a temporary bladder.

With the continued development of fast curing resins, the limitation for most lining jobs is still the lateral cutting so there is still incitement to develop better cutters

Erik H. Nielsen is owner of AMerik Engineering LLC, Marietta, Ga.