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There are many variables to consider when designing a composite repair, including:
Finding a product that is engineered to the exact specifications of a given scenario will not only offer the best design required to provide a functional and lasting repair, but it can also reduce costs. There are many other conditions, such as bending or combined loading, that the repair must address.
These conditions can more easily be considered if the repair is custom designed instead of assuming that an off-the-shelf product has already considered these loads. “Pre-designed,” ready-made repair products should only be used to address very specific situations, which should be clearly and plainly understood by their manufacturer and communicated to you.
Read a more detailed answer under Misconception 1 in our white paper: “5 Common Composite Repair Misconceptions.”
The universal answer, no matter who the manufacturer, is yes. Inspection standards can be vague and the development on education is lacking, but it’s the responsibility of the operator, who is the final decision-maker on product selection, to know if the composites have been inspected for use.
There are several non-destructive tests (NDTs) to analyze defects within the pipe’s walls and the surrounding composite material, regardless of composite the manufacturer.
Read a more detailed answer under our Composite Inspection: Non-Destructive Tests (NDTs) document or under Misconception 2 in our white paper: “5 Common Composite Repair Misconceptions.”
The words “temporary” and “permanent” seem to mean something different to each operator, manufacturer and auditor. A general definition for both could be:
All internal wall loss defects, external abrasion or extremely high fatigue scenarios will be treated as temporary, as well as cracking in the composite or further corrosion growth under the repair. If no growth is expected, however, meaning the current and end-of-life conditions are predicted to be the same, then a permanent composite repair becomes a viable option, but not before considering composite creep and cyclic fatigue life of the composite and the pipe.
Read a more detailed answer under Misconception 3 in our white paper: “5 Common Composite Repair Misconceptions.”
As it currently stands, composite repairs should only be considered a temporary repair for situations where the crack or crack-like feature cannot be removed without additional, focused testing. As a temporary repair, composites can bridge the gap until a more permanent solution can be installed.
Read a more detailed answer under Misconception 4 in our white paper: “5 Common Composite Repair Misconceptions.”
Maintenance engineers should pay close attention to a product’s fabric or laminate construction. Uni-, bi-, tri- or quad-directional fabrics are important structural characteristics to make sure you’re selecting the right composite for your repair.
Uni-directional: The fibers in this material are oriented and aligned in a single direction, making these fabrics extremely strong in that direction but extremely weak to any loads not parallel with the fiber construction.
Bi-directional: These fabrics are created in a 0°/90° woven configuration, which can support both the hoop and axial stresses if designed accordingly, but it’s weak when exposed to torsional or shear forces along the 45° line. The thin composition of bi-directional fabrics makes them relatively flexible and easily formed to complex shapes when wet or dry.
Tri-directional: The fabric is typically engineered in a stacked fashion (great for leak repairs) with strength in the hoop direction. The alignment along the 0°, +45° and -45° lines provides greater load-bearing capabilities and makes it the best option for conforming to irregular shapes.
Quad-directional: This composite is relatively strong in every direction and is ideal for leak repairs due to its strength and sequencing. Its thick- and stiffness in all directions makes these fabrics extremely difficult to apply to complex shapes. Quad-directional fabrics have the highest average overall strength and modulus in stress but the lowest in any single direction.
Randomly oriented: These fabrics contain no directional preference and are typically used in low-stress applications in a preventative measure because their construction provides minimal strength.
Read a more detailed answer under Misconception 5 in our white paper: “5 Common Composite Repair Misconceptions.”
Tap Test: A great preliminary test to determine if further inspection is needed. An inspector uses a metal object, like a quarter, to tap along the outside of the composite and use the resulting sound to determine if a defect exists within the composite. More sophisticated methods exist for this form of testing: Tap Hammer, RD3 and CATT
Phased Array: This ultrasonic method can be used to detect defects within the pipe, voids between the pipe and the composite repair, and the voids or delamination within the composite itself. The results can be viewed as either a C-scan (2D, top-down view) or a B-scan (2D, side-on view)
EMAT: This method inspects pipes and composites by producing electromagnetic waves that interact with the conductive materials found in some composite repairs, which give off their own electromagnetic waves. The combination of the waves creates sound waves that are used to locate damages and defects. EMAT does not need to come into direct contact with the inspected area.
Pulsed Eddy Current: This electromagnetic testing method uses a transmitter to produce alternating currents that induce looping currents, or eddy currents, in nearby conductive materials—in this case the substrate. Existing defects interfere with the flow of the current and are presented in the form of a color-coded grid based on severity of wall loss.
Digital Radiography: This method, also known as X-ray, uses penetrating radiation to inspect delamination and disbanding within the tested materials and find defects in both the composite and the pipe wall. This option is primarily chosen for pipes that are already completely exposed. Transmitted waves that haven’t been interrupted by defects help form an image that gives an actual photographical representation of the insides of the pipe or composite.
Microwave: This method detects delamination and disbonds in non-conductive materials, so not carbon fiber composites. Transmitted waves are reflected back when meeting a void or discontinuation in material, and the voids are identified as areas of delamination, disbonding or gouged composite and case the microwaves to be reflected back to the inspection instrument at a different rate.
Thermography: Thermography can find defects by detecting the change of thermal activity within a material and creating a heat map of the surface of a stressed object by using an infrared camera and equipment. This method is better suited for defects closer to the surface because of the energy required is higher the deeper the defect is in the ground.
Read a more detailed answer under Misconception 2 in our white paper: “5 Common Composite Repair Misconceptions.”