Strengthening of Pipes

According to ASCE’s 2009 Report Card for America’s Infrastructure, leaking pipes lose an estimated 7 billion gallons (26 billion liters) of clean drinking water daily. Additionally, a large number of pipes in water distribution networks as well as in oil, chemical and power industries are badly deteriorated and require repair or strengthening. These pipes are usually pressurized, and the deterioration of reinforcement in prestressed concrete cylinder pipes or loss of thickness in steel pipes reduces the strength of the pipe to resist the internal hoop stresses. When unattended, the consequences of such failures are grave and can leave entire neighborhoods under water or force emergency shutdown of a plant.

A common strengthening approach in the last decade has been to apply one or more layers of carbon fabric to the inside surface of the pipe. The fabrics provide a pressure vessel inside the pipe with adequate strength in the hoop and longitudinal directions. While very effective, the required construction time associated with the wet lay-up method has been a major drawback for this system, especially when miles of pipeline require such repairs.

The super laminates offer several advantages over the wet lay-up system. First, the mechanical properties of the products can be independently tested prior to installation inside the pipe, allowing the owners to reject any defective products. This is a major advantage which is not possible with the wet lay-up approach; in the latter case, samples of products are prepared in the field during installation and tested days later. If found defective, significant time and money will be wasted to remedy the problem. Super laminates have a QC control at the manufacturing facility and can be ISO 9000 approved; they provide a finished product to the jobsite.

Secondly, super laminates significantly reduce the construction time by allowing the most time consuming task (i.e. saturation of fabric and removal of air bubbles) to

be done in the manufacturing plant instead of inside the pipe. The laminates marketed under the trade name PipeMedic™ by QuakeWrap, Inc. are manufactured per project design requirements in advance and are taken into the pipe through manholes. The flexibility of the laminates allows them to be wrapped into small coils that can pass through manholes that are typically 24 inches (600 mm) in diameter. Once inside the pipe, when the coil is released, the elastic memory of the super laminates forces them to snap against the surface of the pipe – like a loaded spring. There are also no air bubbles to be removed. No major resin equipment is required onsite to install the laminate. There are also issues regarding introducing mechanical equipment through the access man way to pipe.

Thirdly, it is possible to include multiple layers of fabric into a single laminate, further reducing construction time. For example, when steel pipes require strengthening, to avoid galvanic corrosion, a layer of glass fabric is typically applied to the surface of the pipe before any carbon fabric is applied. This protective layer can be incorporated in the super laminate, so that instead of two layers of fabric (one glass and one carbon) applied in the field, only a single super layer of laminate is applied. In other cases, the strengthening requirements may need more than one layer of carbon. Once again, these layers of fabric can be incorporated into a single sheet of super laminate. All of the above attributes introduce huge efficiencies in pipeline rehabilitation. Savings as much as 80% or more in construction time are not uncommon. Such significant reduction in repair time makes many larger retrofit projects possible, where the water authority, for example, could not afford the long shutdown time required for conventional wet lay-up repairs.

Installation involves applying a thin layer of epoxy putty to the back of the super laminate and attaching it to the surface of the pipe (Figure 3). No effort is required to remove the air bubbles as the super laminates are pre-cured and there are no air bubbles to deal with. Depending on the diameter of the pipe, the elastic memory of the coiled super laminate may cause it to snap inside the pipe and bond to the host pipe with little effort. Super laminates can be rapidly installed in rings up to 60 inches (1.5 m) wide along the length of the pipe. Continuity of the rings is achieved by adequate overlap lengths in the hoop and longitudinal directions. Thus, a pressure vessel having adequate strength in the hoop and longitudinal directions can be quickly constructed inside the host pipe. This is an outcome that has been impossible up to now with the narrow unidirectional laminate strips.

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