Technology Report Released For Force Main Rehab

December 2010 Vol. 65 No. 12

Rehabilitation of sewer force mains
In rehabilitation, the existing pipe becomes part of the renewal work. Methods include spray-on linings, close-fit linings, CIPP and woven hose lining systems. Technologies for each of these categories are discussed in this report, including cleaning requirements prior to rehabilitation. Because only limited rehabilitation work has been undertaken to date on sewer force mains, many of these systems were originally developed for water main rehabilitation, but are adaptable to sewer force mains.

Spray-on linings are one of the easiest rehabilitation methods when the objective is to provide corrosion protection to the interior surface. They include cementitious and polymer materials. A new family of polymer spray-on linings, base on the use of polyurea, is finding rapid acceptance for lining manholes, wet wells and other structures including pipes, exposed to corrosive environments. The benefits of polyurea are its fast cure and that it can be sprayed to a thickness of up to two inches, potentially functioning as a structural or semi-structural liner, as well as providing corrosion protection.

Close-fit liners, also called modified sliplining, are another method of rehabilitation. This process involves use of a thin walled liner with an outside diameter similar to the inside diameter of the pipe being rehabilitated, in which the diameter of the liner pipe is reduced for easy insertion. Polyethylene (PE) pipe is used for the diameter reduction process known as symmetrical reduction, and PE and polyvinyl chloride (PVC) pipe are used in the fold-and-form diameter reduction process.

CIPP is the leading method for rehabilitation of gravity sewers. Many new variants have recently been introduced. The variations are primarily in tube construction, method of installation, curing method, and type of resin.

Woven hose linings are made from either polyester, glass or aramid fibers woven into a hose-like configuration. The three types of systems include adhesive backed linings, non-adhesive backed linings, and glass-reinforced thermoplastic linings.

Replacement technologies
Several technologies are available for offline and online replacement. The most common offline method is open cut, which involves the installation of new pipe without regard to the line and grade of the existing pipe.