Composite pipe repairs gain acceptance

Composite repairs have gained greater acceptance among asset owners and equipment operators because they provide an engineered, durable, and affordable solution and they comply with international engineering standards.

11/04/2010


Composite repairs have gained greater acceptance among asset owners and equipment operators because they provide an engineered, durable, and affordable solution and they comply with international engineering standards.

Three-component composite repair systems are typically composed of paste grade material, resin, and reinforcement sheet. As the composite repair system must form a bond with the substrate to be repaired, it relies upon the adhesive quality of the base material or resin for its strength. Paste grade epoxies can be used as base materials based upon their excellent adhesion, mechanical properties, and erosion-corrosion resistance when compared to other nonmetallic systems such as polyurethane, methacrylate, alkyd, vinyl, and polyester-based polymers and resins.

A resin film is applied to the reinforcing sheet to eliminate wicking and capillary failure modes along the fiber strands of the reinforcing sheet. The reinforcement sheet are usually made out of carbon or glass fibers. Carbon fiber sheets are more costly, more rigid, and difficult to cut, design, and apply, in comparison with glass fiber. Glass fiber is less rigid, often increasing the long term cycling performance for such a solution.

 

Repair standards

The growth in acceptance and usage of composite repair systems is inherently related to the availability of standardizing documentation. Two of these standards are ASME PCC-2 and ISO /TS 24817:

·                     ASME PCC-2: Repair of Pressure Equipment and Piping

Article 4.1 provides the requirements for pipework and pipeline repair using a qualified nonmetallic repair system. It defines repair systems as those fabricated of a thermoset resin used in conjunction with glass or carbon fiber reinforcement among other allowed materials.

It provides guidance in assessing defects stemming from external corrosion involving structural integrity damage or not, internal corrosion, and leaks. The standard covers the methodology to follow for designing such repair systems, along with some other design considerations such as external loads, cycling loading, fire performance, electrical conductivity, cathodic disbondment, and environmental compatibility.

·                     ISO/TS 24817 “Petroleum, Petrochemical And Natural Gas Industries-Composite Repairs For Pipework-Qualification And Design, Installation, Testing And Inspection”

This standard covers the requirements and recommendations for the design, installation, testing, and inspection for the external application of composite repairs to pipework suffering from corrosion or other source of damage. This is damage commonly found in the oil and gas industry.

This standard defines composite repair laminates as those with carbon, glass, polyester, or any other similar sort of reinforcement material in a polyester, vinyl ester, epoxy, or polyurethane matrix. The standard also provides mathematical guidance in assessing external and internal corrosion problems with or without structure integrity damage.

While both standards give extensive information and guidance on how to design, apply, test, and inspect composite repairs systems, the ISO/TS 24817 standard allows for the application of repairs onto more complex geometries such as damaged clamped surfaces, bends, T-shaped piping, reducers, flanges, and cylindrical vessels among others. It also considers the repair expected lifetime in the design equations.

 

Training

Compliant composite repairs differ from other traditional noncompliant repair systems. Not only do compliant composite repairs rely on a pre-qualified material and pre-defined mathematical design but also on competent application craftsmanship. That is why all personnel in charge of the execution, inspection, and design of such repairs shall be properly trained and validated by the composite repair manufacturer. The validation process is addressed to train and certify installers, supervisors, and designers of composite repair systems.

Potential installers and supervisors get off-job training and initial validation in a training environment where they get theoretical and practical instructions in the installation and supervision of composite repair systems. Installers complete a test piece repair that is inspected and destructively tested to determine how well the repair was performed..

 

Repairs

Composite repairs can be designed for type A and B defects. Type A defects are those within the substrate, not through-wall and not expected to become through-wall within the lifetime of the repair system (Picture 1). This type of repair is considered to be relatively easy as it only requires structural reinforcement.

Type B defects compromise the structural integrity of the system and require through-wall sealing as well as reinforcement (Picture 2).

This is why they are considered to be more complex repairs. The geometry of the repair can range from a straight pipe section, bend, tee, flange, reducer, to a cylindrical vessel. The level of complexity in the repair will increase in the same order.

Once the type of defect and geometry of the repair are confirmed, the designer calculate the repair parameters: the thickness of the composite repair, the axial extent of the repair, and number of required wraps.

 

Execution

Prior to the application, the surface must be prepared and contaminants removed. The composite application should begin as soon as the surface is prepared. Application should commence as soon as the surface preparation activity has been completed.

The first layer of paste grade material is very important as it levels the substrate, which is likely uneven or pitted due to external corrosion. Without this paste grade material, the reinforcement sheet would be less likely to bond with the substrate. This is why the paste grade material should be pushed deep into the substrate profile in order to minimize the risk of air entrapment.

The reinforcement sheet should then be wetted with the resin and wrapped over the first layer of paste, maintaining a pre-fixed degree of overlapping thorough the axial extent of the repair. In order to achieve intimate contact between layers, firm hand-pressure should be exerted in every wrap.

The angle at which the reinforcement sheet is laid should be alternated in every wrap to make the fabric fibers as multidirectional as possible, hence ensuring that the repair is strong in all directions.

The same procedure should be repeated until the required wraps and composite repair thickness are achieved. The final layer should be of paste grade material to ensure that the last reinforcement sheet wrapped around the repaired surface is completely covered and is therefore protected from mechanical damage. Picture 3 depicts a three-component composite repair after completion.

 

Conclusion

Three-component composite repair systems allow the asset owner and/or equipment operators to restore weakened and/or damaged substrates by means of an engineered and compliant solution. These systems are designed to extend the lifetime of piping systems and substitute temporary repairs.

Good communication among all personnel involved in the composite repair process is fundamental in bringing the repair to fruition. Composite repairs are indeed the right solution for extending the lifetime of equipment in an efficient and reliable manner.

 

Osmay Oharriz, C.E. has worked at Belzona, Inc for twoyears. He is responsible for the Oil & Gas Industry and is an integral part of Belzona’s Engineering team. He can be contacted at ooharriz(at)belzona.com.



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