Abstract
A process to detect damage to a bonded composite repair of metal equipment. The process includes the steps of monitoring electrical resistance in a direct current impressed current cathodic protection circuit having a power supply and an anode in electrical communication with metal equipment having a bonded composite repair thereto. Deterioration of the bonded composite repair is detected based on a change in the electrical resistance of the circuit.
Claims
1. A process to detect damage to a bonded composite repair of metal equipment, which process comprises: monitoring electrical resistance in an impressed direct current cathodic protection circuit having a power supply and an anode having a negative side connected to and in electrical communication with metal pressure vessel equipment having a bonded composite repair thereto wherein said bonded composite repair includes conductive composite materials having carbon fibers; and detecting deterioration of said bonded composite repair and detecting deterioration of contact between said composite repair and said metal pressure vessel equipment based on detection of a change in said electrical resistance.
2. The process as set forth in claim 1 wherein said change in resistance is an increase in resistance.
3. The process as set forth in claim 1 wherein said impressed direct current cathodic protection circuit is an existing cathodic protection system for said metal pressure equipment.
4. The process as set forth in claim 1 wherein said bonded composite repair includes a layer of non-conductive fiber and a layer of said conductive composite materials.
5. The process as set forth in claim 1 including the additional step of activating an alarm if said change in electrical resistance is outside of set parameters.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 illustrates a simplified diagram of a known impressed current cathodic protection system (ICCP) for a pipeline;
(2) FIG. 2 illustrates a top view and side view of a width-tapered-double-cantilevered beam used to test the invention;
(3) FIG. 3 illustrates simplified diagrams of width-tapered-double-cantilevered beam specimens representing increase in crack length used to test the invention;
(4) FIG. 4 illustrates a chart or graph showing applied load and electrical resistance measurements versus displacement changes;
(5) FIG. 5 illustrates an image of a width-tapered-double-cantilevered beam specimen used to test the invention;
(6) FIG. 6 illustrates a chart or graph of crack length propagation and resistance measurements versus fatigue cycles;
(7) FIG. 7 illustrates a graphic image of installation of a repair utilizing the present invention including use of a bare copper wire on an outer surface of the repair;
(8) FIG. 8 is an exploded view of a bonded composite repair constructed for testing of the present invention;
(9) FIG. 9 are simplified drawings showing a bonded composite repair constructed for testing before damage and after damage to the bonded composite repair;
(10) FIG. 10 is a graphic image of a bonded composite repair including embedded sensing wires for damage sensing; and
(11) FIG. 11 illustrates a chart or graph showing voltage and pressure measurements versus time.
DETAILED DESCRIPTION OF THE INVENTION
(12) The embodiments discussed herein are merely illustrative of specific manners in which to make and use the invention and are not to be interpreted as limiting the scope.
(13) While the invention has been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the invention's construction and the arrangement of its components without departing from the scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification.
(14) The present invention provides a process and system to detect damage to a bonded composite repair of metal equipment.
(15) To verify the process and system, a small prototype known as a width-tapered-double-cantilevered beam (WTDCB) specimen was created to simulate the real field of bonded composite repair systems of metal pressure vessel equipment, ship, or any metal structure. A schematic of a top and side view of a WTDCB specimen is shown in FIG. 2. The WTDCB specimen contains steel adherent which represents a wall of metal pressure vessel equipment, and composite adherent which represents the bonded composite repair that is made of carbon fibers and wet-out material. The carbon fibers are conductive so that the electrical resistance changes during quasi-static and fatigue tests, enabling the in-situ inspection of defects in a composite. The resistance measurements increase when the crack length increases because as crack length gets larger, the contact between the adherent and substrate is reduced, which simulates de-bond damage, as shown in the diagrams in FIG. 3. A fiber break inside a composite adherent increases the resistance measurement due to disconnect.
(16) For quasi-static testing, a constant current was applied using a laboratory power supply and a LabVIEW program measured the resistance change during the test. The chart or graph in FIG. 4 shows the applied load in newtons and the resistance measurements in ohms versus the vertical displacement in mm of the WTDCB specimen during a quasi-static test. The applied load and the resistance are shown on vertical axes while the displacement is shown on the horizontal axis. As the applied load curve increases, the resistance curve increases as well, which verifies that electrical resistance increases with displacement.
(17) FIG. 5 shows an image of a WTDCB specimen with the system of resistance wires. Aluminum conductive tape was used to attach the wires to specimen.
(18) In addition to confirming that the resistance monitoring approach works, a fatigue test was performed to simulate a field operation of bonded composite repair. These changes can predict, or warn, when a composite has been damaged and might fail.
(19) FIG. 6 is a chart or graph of crack length propagation in millimeters and resistance measurements in ohms versus the fatigue cycles for a fatigue test. The crack length in millimeters and the resistance in ohms are shown on vertical axes while the fatigue cycles are shown on the horizontal axis. The resistance measurement increases as the crack length increases over fatigue cycles as shown in FIG. 6. The behavior of the resistance measurements confirms how the resistance measurement behaves when fatigue cycles increase.
(20) A correlation between crack length and electrical resistance has accordingly been shown.
(21) In summary, detection of damage of a bonded composite repair of metal equipment is detected by a change in resistance of an existing cathodic protection circuit system.
(22) FIG. 7 illustrates a graphic image of installation and construction of a bonded composite repair utilizing the present invention including use of a conductive wire, such as a bare copper wire, on an outer surface of the composite repair.
(23) FIG. 8 illustrates an exploded view of a bonded composite repair constructed for testing of the present invention. A metal substrate 60 simulating metal equipment was prepared with a through-wall defect such as a hole to simulate an actual metal vessel hole or defect. A conductive primer 62 was applied to the top surface of the metal equipment to be repaired. Alternatively, a non-conductive primer to which conductive material, such as carbon black, has been added might be used. Thereafter, a non-conductive fiber 64, such as fiberglass, was applied thereon.
(24) Thereafter, a conductive fiber 66, such as carbon fiber, was laid down on top of the non-conductive fiber 64.
(25) FIG. 9 illustrates two simplified drawings showing a bonded composite repair, such as shown in FIG. 8, before damage to the bonded composite repair and after damage to the bonded composite repair. The upper drawing illustrates flow of current before defect in the bonded composite repair. The lower drawing shows current flow when a defect, such as a blister area, has propagated in the composite repair. The flow of voltage is altered due to defect in the composite repair.
(26) FIG. 10 illustrates a graphic image of a bonded composite repair including embedded sensing wires.
(27) FIG. 11 illustrates a chart or a graph showing voltage and pressure measurements versus time in seconds. The voltage change is shown due to growth of a blister or defect in the simulated pipe repair. Oil was introduced through the hole in the metal substrate and then pressurized using a pump until failure. The plot shows the applied pressure and the measured voltage drop across two of the wires in the simulated system. The plot shows an increase in voltage drop as the blister expands.
(28) The invention may be enhanced by including an alarm in the event resistance changed outside of set parameters, such as a range of parameters.
(29) The invention could further be enhanced by including an algorithm to eliminate false positives, such as from stray electrical fields generated by a local AC power source, for example.
(30) Whereas, the invention has been described in relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the scope of this invention.
