Composite overwraps

If the bond between the copper tube and the A286 support tube is neglected, the centrifugal pressure of the copper on the overwrap is 2.52 MPa (366 psi) at 12,000 rpm, which produces a hoop stress of 298 MPa (43,200 psi) in the composite overwrap. The hoop stress in the overwrap itself, due to the 12,000-rpm rotation, is 150 MPa (21,700 psi). Hence, the combined hoop stress in the overwrap is 447 MPa (64,900 psi) at design speed and 541 MPa (78,500 psi) at the overspeed (13,200 rpm) condition. The observed tensile strength in the hoop direction for the composite at 77 K was —896 MPa (130,000 psi). Hence, sufficient structural protection under rotation should be provided by the overwrap. Warm tests on the complete generator were recently conducted up to 12,000 rpm with no apparent problems with the shield construction. 

Type III— metallic liner with full composite overwrap (mainly carbon fiber)... 

FIGURE 8.1 Sources of Heat Leak into a Cryogenic PropeiiantTank. Shown in the pressurant gas transfer lines are high pressure Composite Overwrapped Pressure Vessei, Pressure Control Assembly (PCA), and HEX. 

NASA (2009) Composite Overwrapped Pressure Vessels, http //www.nasa.gov/ centers/wstf/laboratories / composite/ index.html. 

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. 

Conventionally, most steel pipelines were repaired by removing the corroded section and replacing it with a new pipe or by reinforcing the defected section with an external steel sleeve (Mohitpour et al., 2003). Recently, fibre-reinforced polymer (FRP) composite overwrap repair systems have been introduced and overwhelmingly accepted as an alternative repair system for pipelines. 

The behaviour of pipes repaired with composite overwraps has been studied by many researchers in order to understand the effects of different parameters such as material properties and loading conditions. 

Freire et al. (2007) carried out an extensive experimental study to investigate the effectiveness of FRP overwrap repair on externally and internally damaged pipelines. They concluded that the use of composite overwrap could restore the burshng pressure resistance of both types of repaired pipes to the level of undamaged pipes. 

In 2006, the first revision of two international codes, one by the International Organization for Standardization (ISO), ISO/TS-24817 (ISO, 2006) and the other the ASME PCC-2 (ASME, 2006), were published to assist engineers in designing a reliable composite overwrap repair. The former is recognised as a general code that covers pipes with different materials from steel to FRP while the latter is specifically focused on steel pipes. 

Many composite overwrap repair systems have been introduced to the pipeline industry, their differences being in fibres, adhesive, resin and method of application. Carbon fibre, glass fibre and aramid fibre (Kevlar reinforcement) are the usual fibres used in these composite systems to provide for the required strength and stiffness. In general, two types of composite repair, namely layered system and wet lay-up system, are currently used for pipeline repair (Figure 10.1). 

FRP overwrap repair systems can be considered as a lifetime repair for the cases where they can retard the growth of external corrosion by isolating the external defect from the corrosive environment. During the past decade it has been proven that FRP is a viable repair system and can be performed adequately under different environmental conditions in industrial projects (Duell et al., 2008). The behaviour of pipes repaired with composite overwraps has been studied by many researchers in order to understand the effects of different parameters (Alexander et al., 2008 Alexander and... 

Saeed, N., Ronagh, H., Virk, A., Ashraf, M., 2012. Investigating the effects of pipe live pressure on the design of composite overwrap repairs. In The Australasian Stmctural Engineering Conference (ASEC 2012). Perth. 

Composite overwrap repairs can provide both strengthening and leak reinforcements to the pipe. Specially formulated resins are required for underwater applications where there are limitations with adhesion and curing. These repairs can be applied in situ without hot work, to partially or completely restore the pressure capacity of a corroded or mptured pipe, with the added corrosion protection benefit. Composite overwraps are primarily suited to onshore or offshore shallow water applications, due to the reliance on personnel to manually apply the composite onto the defect area. In addition, the overwraps require stringent surface preparation to ensure optimum adhesion and effectiveness of the repair, which is not always practical under field conditions. 

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