Patent Application
20210040623
This disclosure relates to cathodic protection, and specifically to a safety system and method of de-coupling cathodically protected structures, e.g., pipelines.
Cathodic protection of structures, for example pipelines, is known in the art (https://en.wikipedia.org/wiki/Cathodic_protection#Applications, accessed 6 Aug. 2019). Cathodic protection is a method of corrosion control whereby the corrosion is transferred to a known body, such as a partially inert anode, away from the structure under its protection. In addition, the Applicant is aware of a current practice whereby, where required, solid-state de-couplers incorporating AC mitigation methods are deployed on structures and pipelines where alternating current (AC) needs to be de-coupled to ground and Direct Current (DC) thresholds need to be preserved and when exceeded DC currents need to be contained and controlled, especially where cathodic protection has been applied.
Cathodic protection generally utilizes two methods, namely sacrificial anode cathodic protection and impressed current cathodic protection, the latter being utilized where higher driving voltages are required. The former method, sacrificial anode cathodic protection, has a limited source impedance and may be benign with regard to generation of hazardous voltages.
Techniques to determine a level of cathodic protection and/or a condition of coatings of buried infrastructure comprise a switching technique applied whereby the cathodic protection current is regularly interrupted to ascertain an “off and on” waveform. The results of the wave form are utilized to determine whatever it is the application requires.
For safety reasons, structures under cathodic protection (i.e., cathodically protected structures) may need to, or it may be desired to, de-couple the structures, with respect to AC and/or DC, relative to ground. De-coupling safety systems, for example, solid-state devices, have been created to perform this de-coupling.
Capacitances utilized in solid-state de-couplers however modify the applied waveform and distort the evidence obtained from the interruption process. In order to avoid the waveform modification, the solid-state de-coupling devices are disconnected from the infrastructure for the duration of the testing and thereby the very reason for installing the de-couplers, to prevent human accident and shocks, is compromised.
Accordingly, the disclosure provides a safety system for de-coupling of a cathodically protected structure, the safety system comprising:
The disclosure extends to a method of de-coupling of a cathodically protected structure, the method comprising:
The switch may be in the form of an isolator.
There may be plural AC components and/or DC components.
There may be additional electrical or electronic components connected or connectable between the structure and ground, for example, connected in parallel with the AC component and the switch. Actuation or disconnection of the switch may not disconnect the additional electrical or electronic components. The additional electrical or electronic components may include circuit elements, like diodes, trigger circuits, resistive and/or reactive elements, etc.
The DC component may include at least one diode, gas discharge tube, thyristor, a DC mitigation circuit and/or a DC control element. The AC component may include a reactive element, an AC mitigation circuit and/or AC de-coupler.
The safety system may be provided by one, or at least one, solid-state device package. The switch may be accessible from an exterior of the solid-state device package. The switch may be actuated by wire or wirelessly.
The method may comprise:
The disclosure will now be further described, by way of example, with reference to the accompanying diagrammatic drawings.
In the drawings:
The following description of the disclosure is provided as an enabling teaching of the disclosure. Those skilled in the relevant art will recognize that many changes can be made to the embodiment described, while still attaining the beneficial results of the present disclosure. It will also be apparent that some of the desired benefits of the present disclosure can be attained by selecting some of the features of the present disclosure without utilizing other features. Accordingly, those skilled in the art will recognize that modifications and adaptations to the present disclosure are possible and can even be desirable in certain circumstances and are a part of the present disclosure. Thus, the following description is provided as illustrative of the principles of the present disclosure and not a limitation thereof.
The circuit satisfies the following formula:
(Icp×Rp)+Vp+Vs=Vg+Vd (1)
Icp may need to be interrupted to obtain values or reading for one or more of:
Also, Vd will change by Icp×Rp after Icp is interrupted.
In clustered rights-of-way and sharing of servitudes in today's times, buried pipelines are often subjected to induced currents from overhead powerlines and the associated imbalances within those powerlines may cause unwanted currents to flow in the pipelines. With presence of high-quality coatings, pipelines are largely insulated and wherever testing facilities are installed to determine the level of cathodic protection, these very test facilities and operation appurtenances become hazardous to those operating and handling equipment in the process of their work on the pipelines.
In order to ensure that any AC voltage induced onto the pipeline or overvoltage condition that arises is effectively removed, solid state de-couplers are deployed. For the AC component to be effectively dealt with, inductive and/or capacitive reactance's connected between the structure and ground provide a pathway for AC to be connected to ground without bleeding of the necessary DC injected by the cathodic protection system.
In some PRIOR ART solid-state de-coupling devices deployed, a further DC mechanism is added to ensure that should the DC rise above or below a specified level, it too, gets shunted away to ground thereby limiting the possible voltage that could appear on the structure pipeline to ground both AC as well as DC.
Various PRIOR ART de-coupling systems for cathodically protected structure exist, which are typically in the form of solid-state or electrolytic de-couplers. Variants of which the Applicant is aware are illustrated in
The de-coupling system for a cathodically protected structures system is usually connected between the structure (the pipeline, in these examples) at contact point A and ground at contact point B.
The DC component 12 is provided between contact points A and B and is thus configured to be connected between the pipeline (contact point A) and ground (contact point B). The AC component 14 is also provided between points A and B and is similarly configured to be connected between the pipeline and ground. The AC component 14 is in parallel with the DC component 12 and there may be additional DC components 12, for example, in parallel between the gas discharge tube and AC component 14. The AC component 14 is a reactive component.
Importantly, a switch 16 (e.g., in the form of an isolator) is inserted in series with the AC component 14. Thus, connection or disconnection of the switch operatively connects or disconnects the AC component 14 between the contact points A and B, and thus between the pipeline and ground.
The various safety systems 10, 20, 30, 40, 50 differ in minor ways:
However, in all of the safety systems 10, 20, 30, 40, 50, the same principle is overarching: the switch 16 is configured to disconnect the AC component 14 but not the DC component 12.
The DC component 12 is not necessarily limited to DC components and may include AC or reactive components (e.g., an inductor as in some of the FIGS.) or other circuitry.
The safety system 10, 20, 30, 40, 50 may be implemented in a solid-sate package. A rating of the switch 16 or isolator may be determined at manufacture based upon steady state conditions for which the safety system 10, 20, 30, 40, 50 is designed, and may be configured to handle multiple operations.
The safety system 10, 20, 30, 40, 50 may have the following technical uses and advantages.
As the AC component 14 is, at least partially, responsible for modifying or distorting electric signals or waves, by disconnecting the AC component 14, such wave-modifying components can be temporarily removed, leaving the DC components 12 still connected, thereby to limit both the DC current that might be on the pipeline as well as any AC on the pipeline. This has the effect that any AC or DC voltages may be reduced to accepted levels and clamped by the DC components without exposing people (e.g., maintenance workers) to undue electrical hazards and/or modifying the applied testing waveform.
Accordingly, the switch 16 may be used to disconnect the AC component 14 only temporarily while tests or maintenance are performed. During this testing or maintenance period, the gas discharge tube of the DC component 12 will continue to be connected, thus enhancing safety. The switch 16 can be closed to reconnect the AC component 14 when testing and maintenance is concluded. It may be advantageous to have the diodes and the discharge tube 12 continually connected to maintain safety without distorting the waveform.
This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/884,425, filed on Aug. 8, 2019, the disclosure of which is hereby expressly incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62884425 | Aug 2019 | US |
