Internal composite repair system

Analytical methods are important for internal composite repair systems to ensure that damaged pipelines are properly analysed to evaluate the system against performance measures. Existing methods specifically focus on external repairs of pipelines with internal repairs still unexamined, even though the concept could potentially be applied to internal repairs. Therefore, the concepts and approaches that could be adopted for analysing unbonded and bonded repairs are considered below. 

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. 

Rehberg, T., Schad, M., Green, M., 2010. Non-metallic Composite Repair Systems for Pipes and Pipelines. Pipe Technology 3R International. Special Edition. 

Alexander, C., Cercone, L., Lockwood, J., 2008. Development of a carhon-fibre composite repair system for offshore risers. In The 27th International Conference on Offshore Mechanics and Arctic Engineering, OMAE2008. The American Society of Mechanical Engineering, Estord, Portugal. 

The unbonded composite repair system can be either rigid or flexible. A rigid composite pipe is installed and cured inside the corroded steel pipe, using the damaged pipe as a form or mould, but is not bonded to the pipe. In this system, the internal composite finer acts as the pipe, with no or minimal contribution from the original pipe. There is no load transfer between the internal composite pipe and the external steel pipe. Therefore, the composite pipe must be capable of carrying the full internal pressure load as well as bending and other external loads. 

To overcome the limitations in the Lame theory when applying to orthotropic composite repair systems, a new modified version of Lame s equations (MVLE) was developed by the authors to undertake the analysis of infinitely long orthotropic cyhnders subjected to internal and/or external pressure. The hoop and radial stresses at any point in the wall cross section of an orthotropic cylinder at radius r are given by the following equations ... 

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

Duell, J.M., Wilson, J.M., Kessler, M.R., 2008. Analysis of carbon composite overwrap pipeline repair system. International Journal of Pressure Vessels and Piping 85, 782—788. 

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. 

Unbonded repair systems for internal pipelines using composite technologies are discussed, by Heavens and Gumbel (2004), on the basis of installation processes, which are the fold-and-form and the slip finer processes. 

Internal repair systems using earbon and glass fibre (GF) composites were reviewed and evaluated by Bmee et al. (2006). Carbon fibre (CF) liner repair was seen as the more promising proeess, having better strength and stiffness characteristics than GF liners. However, the developed and investigated CF liner systems were patch repair only (sectional liners) and bonded to the steel pipelines. The details of these tests are discussed in the following sections. 

Some novel analytical methods that can be used to effectively design composite materials for internal repair were presented. Finally, available experimental studies conducted on internal FRP repair rehabilitation systems for steel pipe were discussed, demonstrating the high potential of composite materials for restoring the pressure capability of damaged pipelines. 

Alexander C, Fracini B (2006) State of the art assessment of composite systems used to repair transmission pipelines . Proceedings of the 6th International Pipeline Conference, Calgary, Alberta, Canada. 

If included in the SAR, detailed OLCs for operation should contain numerical values of limiting parameters and operability conditions of systems and components. The corresponding requirements for surveillance, maintenance and repair to ensure that these parameters remain within acceptable limits and that systems and components are operable should also be specified and, where appropriate, justified by means of a PSA. The actions to be taken in the event that operational limits and conditions are not fulfilled should also be clearly established. In some cases, essential administrative aspects, such as the minimum shift composition and the frequency of internal reviews, are also covered by these conditions. Reporting requirements for operational events should also be covered. Further discussion on matters to be covered in this chapter of the SAR is provided in Ref. [39]. 

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