Composite repair system materials

The use of fiber-reinforced composite materials for pipeline repairs was developed during work at Southwest Research Institute and Battelle in the late 1980s (Fawley, 1994 Stephens and Kilinski, 1994). There are two basic types of composite repair systems preformed (composite sleeves) and wet lay-up (composite wraps). The first commercially available system was Clock Spring , which consists of an E-glass/polyester resin-based composite material preformed into a multilayer coil that is installed using an adhesive (Figure 4.4). 

The modified Lame s coefficients and the corresponding MVLE for common available orthotropic material cylinders were studied, and it was concluded that, for currently available orthotropic materials, the values of a and jS are not equal to each other. For isotropic materials, a and jS are equal to 0 and —2, and Eqns (13.7) and (13.8) convert to Isotropic Lame s form as Eqns (13.3) and (13.4). Internal composite repair systems can be split into two cylinders using contact pressure, as depicted in Figure 13.7. Then the system can be analysed by considering strain compatibility at the composite—steel interface and appropriate boundary conditions. 

Fabricating and repairing complex materials systems. Mechanical methods currently in use (e g., riveting of metals) cannot be applied reliably to the composite materials of the future. Chemical methods (e g., adhesion and molecular self-assembly) will come to the fore. 

Gurit has developed and launched the RENUVO blade-repair system (see Section 10.1.2) which overcomes the above disadvantages, Cripps (2011). Depending on the thickness of the composite laminate, a high intensity UV cure of 60-180 s cures the material to its full value. The RENUVO materials are specially formulated, and exhibit excellent handling, adhesion and cured properties at temperatures as low as +5°C and at high humidity... 

Unlike the case of a composite clamp which is manufactured under shop-floor conditions that allow close control of the curing process, overwrap repairs are applied and cured in the field. Hence, it is not always practical to replicate laboratory cure conditions and the surface preparation of the substrate that have been used to determine the properties and performance of the overwrap repair system. To this end, a good understanding of the cure behaviour of the overwrap composite material and the composite—substrate interface properties is essential to ensure that repairs are properly applied and the acceptable performance is achieved in the field. 

However, most internal repair methods are used for low operating pressure pipelines and only to restore leak tightness (Toutanji and Dempsey, 2001). Also, these internal repair systems are considered to cause reductions in the inside diameter of pipelines that may hinder the ability to clean and inspect them using traditional tools. Thus, the use of composite materials for internal repair of pipes presents a number of difficulties that have yet to be fully explored. 

A limited number of stodies have been conducted on the internal repair of steel pipelines using composite material systems. As a consequence, only a few industries have used composite technologies for internal repair. In their report, Bruce et al. (2006) indicated that internal repair would have the best economics for underwater repair locations as it reduces out-of-service time and does not require divers and habitats. Such economics arise because the majority of the gas transmission line companies in the United States consider the ability of the pipeline to remain in service during internal repair to be very important. Moreover, they would considCT internal repair, even if the pipeline needs to be out of service (no flow), only if the pipeline remains pressurised and the line can still be inspected by a pipe inspection gauge after repair. However, these companies have indicated that they would consider performing a repair from inside the pipe once a proven and accepted internal repair system becomes available. Thus, the selection of the most appropriate technique of renovation, particularly on the internal repair of high-pressure and deep water pipeline applications, is a critical and ongoing issue. 

Figure 13.7 (a) Internal composite repair components and (b) structural idealisation and composite material axis system. 

Advanced materials systems based on polymers, ceramics, and composites are constmcted by assembling components to create stmctures whose properties and performance are determined by the form, orientation, and complexity of the composite stmcture. The properties of these assemblages are determined not by the sum of weighted averages of the components but rather by synergistic effects in intercoimected phases. For this reason, the study of fabrication of hierarchical assemblages of materials, as well as the study of mechanisms for repairing defects in assembled stmctures, must be supported by fundamental research. 

Polymer resins were first introduced in the early 1940s as an aesthetic alternative to repair defects in anterior teeth. Some of the first resins were unfilled polymers of methyl methacrylate. Presently, these unfilled resins have been replaced by filled composite materials that limit the problems associated with polymerization volume shrinkage, abrasion or wear resistance, mechanical properties, water sorption, solubility, and thermal expansion. Polymeric composite materials generally consist of a monomer resin, a ceramic filler, a polymerization initiator or initiating system, and a coupling agent which binds the polymer... 

One of the most exciting fields of research involves the study of composites, materials with two or more components with properties different from those of the components. Composites have revolutionized fields as diverse as sports and recreation and air transportation and military equipment. Another active field of research focuses on biomaterials, synthetic or semisynthetic products that have applications in living systems. Today researchers are developing artificial skin, blood, nerves, and other body components that can be used for the repair of damaged tissues. Nanotechnology is perhaps the most revolutionary of all areas of materials research. The subject deals with components of very small dimensions, comparable to those of atoms and molecules. Smart materials are yet another topic of... 

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