A+ Wrap

April 18, 2018
The Evolution of Composites: Situational Repair Setbacks

Posted by: Natalie Swift

Last month, we discussed how pre-formed fabrics used in rigid coil repair systems compared to form fitting fabric used for our composite wrap installations. Achieving intimate contact between the pipe and repair system is more difficult using a pre-formed system instead of a form fitting one. Additionally, if the repair includes a complex geometry, it’s impossible to even consider a rigid coil system.

Today we will look at other situational repair setbacks you may find using a rigid coil system, and how these difficulties can be alleviated with a composite wrap system.

Designed Repairs

Rigid coil systems use a fixed layer count repair for all defects independent of the defect severity. This means that they will be over-designed for most repair scenarios, and possibly even under-designed for some scenarios with high grade, large diameter, thick walled pipe with extensive metal loss. Some of these repair systems do not fully conform to ISO 24817 or ASME PCC-2 design standards.

A+ composite repairs designs always consider the specific defect conditions to provide an appropriate layer count based upon either the ASME PCC 2 or ISO 24817 design standards. The FormaShield and Atlas systems can be further customized to handle high temperature and chemically corrosive environments, an option not available with rigid coil systems.

Fiber Orientation

Another potential disadvantage of using some rigid coil systems instead of A+ is the fiber orientation. Most rigid coils use a unidirectional fabric with fibers only in the hoop direction, which means that the axial strength only comes from the resin matrix. The fiber reinforcement is much stiffer and stronger than the resin, so unidirectional composites will only provide support in one direction. This makes unidirectional composites less popular choices for defects with large thrust loads or bending moments—circumferentially oriented corrosion, girth weld defects and wrinkle bends. Additionally, improper handling of the coils can cause circumferential tearing.

All MIS products have multidirectional fibers. The A+ and Atlas systems are bidirectional while the FormaShield is tridirectional, so they will provide structural reinforcement in both the hoop and axial directions. This makes them better choices for defects with large axial stresses.

Splashzone and Underwater Repairs

A+ wrap is pre-impregnated with a moisture-cured polyurethane resin, so a wet application environment will actually help the system cure. A+ wrap can even be applied underwater when the standard PPR primer is replaced with Splashbond. Splashbond primer will displace the water on the pipe allowing the repair to bond to the surface. These attributes make A+ wrap a strong choice for repairs in the splashzone or underwater. Rigid coil systems cannot be applied in wet conditions.

Material Hazard

Rigid coil systems that use methyl methacryalate to bond the layers together pose a greater hazard than materials used in the A+ system. Methyl methacryalate’s fumes are not only very pungent but they are also highly flammable, with a flash point at 11 C. The adhesive and resin used in the A+ system have a mild odor and are non-flammable, with a flash point at 120 C.

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Category: Feature Articles, Pipe Wrap

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