Trenchless Technology Center
Louisiana Tech University

Water Environment Research Foundation

Rehabilitation of defective sewer laterals restores impaired structural integrity and reduced hydraulic capacity of these pipes, as well as improves the leak-tightness of pipes and connections and hence eliminates or minimizes groundwater infiltration into the sewer system and/or exfiltration of wastewater into the surrounding soil. Rehabilitation also prevents root intrusion through defects into the pipes, which is a serious problem for many agencies.

Sewer laterals can be repaired or replaced either over their entire length or only in selected parts.

A number of trenchless rehabilitation methods have been developed for the purpose of lateral repair—the principal methods in use today being cured-in-place (CIP) relining products, replacement by pipe bursting, chemical grouting, and flood grouting. Robotic repairs are a relatively new method, whereas mechanical repair sleeves for sectional repair of laterals are less frequently used.

The lateral rehabilitation methods shown below are included in our database. Click on the link to see details.
CIP Relining
  CIP, Standard Liners
  CIP, Remotely Inverted Standard Liners
  CIP, T-Liners
  CIP, Short T-Liners
  CIP, Top Hats
Pipe Bursting
  Static Pull
  Pneumatic Bursting
Lateral Chemical Grouting
  Grouting, Mainline Packers
  Grouting, Push Type Packers
Flood Grouting
Robotic Repairs
  Robotic, Pressure Applications
  Robotic, Non-Pressure Applications
Mechanical Repair Sleeves
CIP, Top Hats

Top Hats are short connection liners that are shaped to seal the connection of the lateral with the mainline. They create a brim (about 3 in.) around the lateral connection in the mainline and extend for a short distance (usually about 6 in.) into the lateral. These liners are installed through the mainline.

These liners are often used when only lateral-to-mainline connections need to be repaired, e.g., in those situations when the mainline and/or lateral have already been CIP relined but the annular space at the connection has not yet been sealed against infiltration. Access to private property is not needed.

CompanyCosmic Tophat LLC AMerik Engineering LLC
Product/System NameTopHat® Top Seal
Product Material
InstallationRemote inversion Remote inversion
Product CureUV-light cure UV-light cure
Lateral, Pipe TypeAny Any
Lateral Dia, Min3 in. 4 in.
Lateral Dia, Max10 in. 6 in.
Lateral Dia, Transition- -
Repair in Lateral, Max18 in. 8 in.
Mainline Dia, Min6 in. 6 in.
Mainline Dia, Max21 in. 21 in.
Repair in Mainline3 in. brim 3 in. brim
Bends in Lateral, 90s- -
Offset of Joints, Max- -
Lateral Protruding, Max< 1/4 in. < 1/4 in.
Active Leaks (Heavy)No No
Lateral CleaningYes Yes
Cleanout (1 or more)Yes No
Pit(s) ExcavationNo No
Entering Private PropertyNo No
Lateral PluggingNo No
Mainline PluggingNo No
Structural RepairYes Yes
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