This article will explore how cured-in-place pipe (CIPP) is being utilized to assist in the rehabilitation of pressurized pipelines. The article provides a brief historical background of CIPP development, compares regular and pressurized CIPP, and illustrates a step-by-step process of a pressurized CIPP.

Generally, regular CIPP is as a rehabilitation method on gravity-fed pipeline sewer system. To differentiate, pressurized CIPP is defined as a rehabilitation method on pressurized pipelines.

CIPP technology was introduced about 50 years ago. It quickly became a popular trenchless technology for pipe repair or rehabilitation. At that time, its application was limited to a gravity-fed system for sewer pipelines. Industry evolution led to a CIPP technology for pressurized pipelines.

Pressurized CIPP was first implemented on a small diameter pipe several decades ago. In the mid-1990s, a semi-structural CIPP was completed on a 60-inch diameter pressurized pipe at a nuclear plant. In 2012, a pressurized CIPP was installed to convert a sanitary sewer to become a force main with 15 psi operating pressure.

How it Differs from Other CIPP Applications

Let's review the differences between regular CIPP on sewer or gravity-fed systems and CIPP on pressurized pipelines. The comparison will be based on its applications, materials, design considerations, and product characteristics. (Read also: Is a CIPP Liner The Right Fit for Your Trenchless Rehabilitation Project?)


Regular CIPP is typically used in gravity-fed systems such as stormwater, sanitary, and combined sewers that have low operating pressures. It is accessible by manholes or underground structures upon completion of the construction. Its physical pipe characteristics can be circular or non-circular, in a straight alignment with a uniform slope. We often find this application in residential projects.

Pressurized CIPP is utilized in sanitary force mains or water mains that have higher operating pressures. It is a closed system with connections to lift stations or air release valves. It’s usually used in a circular pipe with an alignment following the existing terrain.


Regular CIPP is a traditional pipe liner and has the option of using a reinforced liner to reduce its thickness in a large diameter pipe. Resins used for regular CIPP are unsaturated polyester (UP), vinyl ester (VE), and epoxy. Regular CIPP material can negotiate bends up to 90 degrees in the pipeline.

Pressurized CIPP requires a reinforced liner to attain the tensile properties required for its application. As such, the traditional liner is not recommended. Resins used for pressurized CIPP are vinyl ester and epoxy. Pressurized CIPP material can tolerate bends up to 45 degrees only in the pipeline alignment.


During the design stage, regular and pressurized CIPP have different considerations. Most of the standard considerations are taken into account in both CIPP designs. Standard considerations would be:

Unlike regular CIPP design, pressurized CIPP design should consider internal pressures under operation, testing, and any other scenario with potential surcharges added to the analysis. Pipe filling, draining and vacuum conditions should also be considered for pressurized CIPP. (Read also: 4 Factors to Consider During Your Pipe Lining Project.)

CIPP Product Characteristics

Physical properties of regular and pressurized CIPP appear to be equivalent. Both have similar flexural strength, abrasion resistance, chemical resistance, and hydraulic capacity. However, only pressurized CIPP has a tensile strength up to 3,000 psi approximately.

Table 1: Summary of Comparison between regular and pressurized CIPP

Regular CIPP

Pressurized CIPP


Pipeline system

Gravity-fed (sewer)


Operating pressure

Less than 40 psi

Up to 200 psi




Pipe characteristics

Circular, non-circular



Straight (typically)

Following terrain


Traditional liner


Not used

Reinforced liner

Used to reduce liner thickness

Used to attain tensile properties


Unsaturated polyester (UP), Vinyl ester (VE), Epoxy

Vinyl ester (VE), Epoxy

Allowable bends

0 to 90 degrees

0 to 45 degrees


Hydraulic capacity



Structural service lifetime









soil (dead) loads



traffic/live loads






internal pressures (operation, surcharges, pipe filling, draining, vacuum)

Not considered


CIPP Product characteristics

flexural strength



abrasion resistance



chemical resistance



hydraulic capacity



Tensile strength


Yes, up to 3,000 psi

CIPP helps to complete repairs without disrupting other parts of the plant or other existing utilities. (Read also: CIPP and the Asian Rehabilitation Market.)

The size required for a workzone/excavation for a CIPP access pit is minimal compared to conventional methods. The spacing in the host pipe should be 2.5 times the nominal pipe diameter at minimum.

An addition of 1 meter all around is typically needed to provide adequate space for the workers on a trenchless worksite; however, the space required is mostly dictated by the pipe diameter. The larger the pipe is, the larger the work zone needed.

An example of a non-disruptive CIPP process for a pressurized system is illustrated below:

  • Step 1: Composite materials are first saturated with a thermosetting epoxy resin system. This can be completed either at the site or in an authorized wetout facility.

  • Step 2: Using water or air pressure, the CIPP tube is inserted into the host pipe. This can be performed by either a pull-in or inversion method.

  • Step 3: Next, hot water or steam is circulated throughout the tube to cure the thermosetting resin.

  • Step 4: Once the pipe is cooled, both pipe ends are cut off and the pipe can be returned to service. Lined sections are connected to the existing system. This can be completed using standard pipe fittings. Any necessary site repair on the pipe should be performed at this stage as well.

  • Step 5: Service connections on the existing host pipe can be robotically restored from inside the lined main pipe.

The use of the robotic mechanism described above focuses the repair process in the host pipe and refrains from interfering or disrupting other existing pipe or systems in proximity of the repair area. It also provides the convenience of remote operation for the workers.


In conclusion, pressurized CIPP developed to date has been an advanced technology in the pipe rehabilitation industry. It has allowed us to provide lining or repair in pressurized pipelines with product characteristics that a regular CIPP is unable to achieve.

Comparison between regular and pressurized CIPP is provided in Table 1. Furthermore, the use of robotic machinery minimizes disruption to existing pipes in the proximity as well as provides remote access for the operators.