StifPipe

StifPipe®is the latest patent-pending technology developed by QuakeWrap, Inc. President, Professor Mo Ehsani for repair of deteriorated pipes, culverts and tunnels. This revolutionary product is a customized per-manufactured Carbon FRP pipe that can be delivered to the job site in any length for quick final assembly inside the pipe. StifPipe® can cut pipeline and tunnel repair costs to a fraction of that by conventional materials and techniques. The evolution and advantages of this product is described below. For a complete description of StifPipe®, please click here and print this 4-page article. Background: Cured-In-Place (CIP) solutions for repair of water and sewer pipelines, storm-water pipes and culverts have become very popular in recent years. These techniques are often trenchless, meaning little or no excavation is necessary to repair the pipe or culvert. In particular, for repair of pressurized pipes, such as Prestressed Concrete Cylinder Pipe (PCCP), the use of Carbon Fiber Reinforced Polymer (CFRP) is a very effective technique. The tensile strength of CFRP is about 2-3 times that of steel and in repair of pipelines that are subjected to internal pressure, two or three layers of CFRP fabric is often sufficient to resist the internal pressures after the host pipe loses its capacity due to corrosion of reinforcing steel wires.

In recent years, however, an increasing number of our clients are seeking a CFRP liner that would meet a more stringent requirement, namely that in the event the host pipe or culvert fails completely, the liner should act as a stand-alone pipe capable of resisting all external loads, such as soil pressure, traffic loads, etc. The design of liners for such loading conditions is controlled by the ring stiffness (rather than tensile strength) of the liner; i.e. the thickness of the liner governs the design. Consequently, for such projects CFRP’s high tensile strength is not as important. Many such projects require a CFRP liner ½ inch or thicker which results in 10 or more layers of CFRP to build up enough thickness (and stiffness) that would resist the external loads without buckling of the liner.

Problem

The Challenge we face is to create a new CIP liner for stand-alone pipe applications with following attributes:

Resist internal pressures

Resist external gravity loads

Lower cost than conventional CFRP liners, and

Faster installation time than conventional CFRP liners.

Solution

To overcome the above short comings, we have developed a truly innovative product called StifPipe®. In doing so, we have combined the results of many years of our R&D and experience in pipeline renovation with decades of R&D in the aerospace industry where honeycomb construction was originally developed. Honeycomb construction simply realizes that the stiffness of an element is determined by the distance between the outer layers; the same principle that makes an I•beam very stiff.

Rather than compiling layer after layer of expensive carbon fabric, we use a specially-designed honeycomb core and bond the carbon fabric to the outer surfaces as skin reinforcement. The result is an extremely lightweight and stiff pipe. For pressurized pipes, the number of layers of carbon fabric on the interior surface of StifPipeo will be designed to resist the internal pressure only, while the entire stiff assembly will resist the gravity and traffic loads.

Unique Advantages: Below is a list of some of the unique attributes of StifPipe®:

Manufactured to any size; unlike conventional pipes, we are not limited to available “round” pipe diameter sizes only. For example, it is possible to line a 60 inch diameter pipe with a StifPipe® having an inside diameter of 58 inches, thereby maximizing the flow capacity.
Made to any profile for maximum capacity; For repair of non-circular pipes, StifPipe® can be constructed to match the existing pipe profile, reduce the loss of cross section and thus maximize the flow capacity. Conventional slip-lining of these pipes with commonly available cylindrical pipes leads to significant loss of capacity.
No lifting equipment; StifPipe® is so light that it can be hand-carried to its final position.
Shorter repair time; Manufacturing the pipe sections off-site before repairs begin will significantly reduce the on-site repair time. The time savings are enormous when compared to installing many layers of carbon fabric inside the confined space of a pipe and delivering the raw materials to the workers under those adverse conditions at locations that could be hundreds of feet away from the access points.
Less volume to grout; By constructing the pipe profile to closely fit that of the existing pipe, little volume will be left to be grouted or filled with resin. This results in materials and time savings during the installation.
Virtually no lead time required; For emergency repairs, unlike conventional pipes, no time is lost waiting for the manufacturing of pipes; the raw material is always available and pipe sections can be ready in 24 hours!
Non-corroding materials; FRP products do not corrode and have excellent chemical resistance.
Can be installed inside leaking tunnels & canals; StifPipe® can be used to line a leaking tunnel or canal and grouted or epoxied in place to eliminates leaks into the tunnel or out of the canal.
Quality Assurance; StifPipe® sections can be tested before they are installed to ensure that they meet the design specifications. In contrast, for wet layup CFRP liners, only witness panels of the fabric are made daily can be tested at a later date. There is a high possibility of substandard installation when so many layers of fabric are to be installed under such adverse working conditions.
Lower Cost; StifPipe® costs less than conventional carbon FRP liners.