The present disclosure relates in general to apparatus and methods for repairing damaged coatings on steel pipe, such as (but not limited to) field repairs to shop-coated pipe used for oil and gas pipelines, and in particular (but not restrictively) to apparatus and methods for repairing smaller areas of coating damage, such as localized nicks and gouges.
Pipelines for transmission of petroleum fluids such as crude oil and natural gas are typically constructed from sections of carbon steel pipe that are butt-welded end-to-end in the field. To help protect the pipe against corrosion, the exterior surface of each pipe section is typically coated with a suitable protective coating (such as but not limited to an epoxy coating), except for bare metal cutback zones at each end to facilitate field welding. The coating is most commonly shop-applied to the pipe sections for optimal quality control. After a field-welded joint has been made between two pipe sections, the weld area and adjacent cutback zones receive a field-applied coating matching or compatible with the shop-applied coating so as to provide continuity of corrosion protection along the full length of the completed pipeline.
It is common for shop-applied coatings on pipe sections to be inadvertently damaged, such as impact damage during loading and shipment of the coated pipe sections, as well as damage from mishandling of the coated pipe sections on the pipeline construction site. In addition, field-applied coatings in the weld area and cutback zones at field-welded pipe joints are susceptible to inadvertent damage. Regardless of where it occurs, such coating damage must be properly repaired before the pipeline can be considered ready for installation and burial in the pipe trench. This is true for any damage that might jeopardize the integrity and protective effectiveness of the coating, even for small and localized areas of coating damage.
Known methods for making field repairs to pipeline coatings include using a propane torch to heat the repair area and melt the existing coating so that it will flow into the damaged area (e.g., nicks or gouges) and/or to facilitate fusing of the existing coating material with any additional coating material that might be applied to the damaged area for purposes of the repair. This method has numerous drawbacks, including:
Another known pipe coating repair method involves the use of a heat gun that directs heated air against the coating repair. However, heat guns typically do not provide sufficient heat to properly heat the affected coating area, or else they provide too much heat and therefore damage the existing coating. As well, the heat from a heat gun typically cannot heat the steel pipe to a sufficient temperature such that the pipe can provide the necessary heat to cure the repair coating material (or at least not without first causing undesirable damage to the existing coating). In addition, heat gun nozzles become very hot and thus pose a burn risk if mishandled by an operator.
A further known pipe coating repair method involves positioning a full-size circumferential induction heater coil around the pipe so as to surround the area being repaired. Induction heating apparatus of this type is commonly used to pre-heat the weld zone at pipeline field joints preparatory to field-coating of the weld zone and adjacent cutback areas, and is quite effective for purposes of field repairs to pipe coatings. However, it is very inefficient to use such comparatively large apparatus to repair small areas of coating damage, due to significant costs (e.g., rental charges, operating costs, and maintenance costs) associated with the induction heating apparatus and the generator (typically a 100 kW generator) required to operate it, plus the large assets typically needed to transport the heating coil and generator (such as a crane truck with a side boom and a custom trailer).
For the foregoing reasons, there is a need for improved and more efficient apparatus and methods for making field repairs to small areas of damage to pipeline coatings.
The present disclosure teaches apparatus and methods for repairing damaged pipeline coatings using a handheld induction heater that delivers heat in a localized area of a coated steel pipe, so as to quickly and efficiently heat the steel pipe to a sufficient temperature for curing an applied repair coating material without causing heat damage to the existing coating. In one embodiment, the handheld induction heater has a main body which houses a pair of 6-inch-diameter induction “pancake” coils connected in parallel. The main body is dimensionally configured to suit the diameter of the specific pipe on which the induction heater is to be used. Optionally, the main body may also incorporate one or more electromagnets to hold the heater in place on the pipe during the heating cycle, and a thermocouple for sensing the temperature of the pipe so that the heater can be automatically shut off when the pipe reaches a preset temperature. Suitable electrical connectors are provided for connecting the heating coils, the electromagnets, and the thermocouple to a suitable power source (such as a 5.0 to 6.5 kW induction generator, which typically will be sufficient for repairing small damaged coating areas). Preferably, the main body is also provided with a suitable handle to allow an operator to manipulate the handheld induction heater.
Advantages of using a handheld induction heater in accordance with the present disclosure for purposes of repairing damaged pipe coatings include the following:
Accordingly, in one aspect the present disclosure teaches an induction heating apparatus comprising an induction generator and an induction heater, wherein the induction heater has a main body made from non-electrically-conductive materials, and houses one or more induction coils. The induction heater is adapted to receive electrical power from the induction generator to energize the one or more induction coils. A bottom portion of the main body is shaped to substantially conform to the shape of an external surface of a steel workpiece on which the induction heater is to be mounted. The configuration and weight of the induction heater are such that the induction heater can be lifted and manipulated by one or more human operators without using auxiliary handling apparatus.
The induction heater may include one or more electromagnets for maintaining the induction heater in a desired position on a steel workpiece.
The induction heater may also include a thermocouple, and may be programmable to de-energize the induction coils when the temperature of the steel workpiece reaches a preset temperature, as sensed by the thermocouple.
In some embodiments, the induction generator has a power generation capability not exceeding 10 kilowatts. In one particular embodiment the induction generator has a power generation capability between about 5 kilowatts and about 6.5 kilowatts.
The main body of the induction heater may have a rectilinear perimeter, but this is by way of non-limiting example only. In variant embodiments, the perimeter of the main body could be of curvilinear, polygonal, or any other geometrical configuration.
In another aspect, the present disclosure teaches a method for repairing a coating on a steel workpiece, including the steps of:
Embodiments will now be described with reference to the accompanying Figures, in which numerical references denote like parts, and in which:
In the particular embodiment shown in
Preferably, a handle 15 (of any suitable type) is affixed to top cover 22 to facilitate handling and positioning of induction heater 10 by an operator. The lower edges 24L of sidewalls 24 are preferably shaped or contoured to conform with the profile of a particular workpiece having a coating requiring repair using induction heater 10. In this regard, it should be noted that although induction heater 10 is primarily intended for repairing coatings on circular pipe, it is also adaptable for use on other coated steel articles including articles with flat coated surfaces or other configurations.
It should also be noted that although the illustrated main body 20 of induction heater 10 has a generally rectilinear configuration, this is by way of example only, as there is no requirement for main body 20 to be of any particular geometric shape. For example, variant embodiments of main body 20 or portions thereof could have a generally curvilinear or other non-rectilinear configuration without departing from the scope of the present disclosure.
In the illustrated embodiment, induction heater 10 includes two electromagnets 30, each being mounted to and extending outward from an associated one of the sidewalls 24, to facilitate positioning of induction heater 10 on the surface of a coated steel workpiece. A pair of circular (“pancake”) induction coils 40 are “stacked” within main body 20, as best seen in
Although not shown in the Figures, main body 20 preferably (but not necessarily) houses a suitable thermocouple (for example, a Type K thermocouple) for monitoring the temperature of a coated steel workpiece so that induction heater 10 can be programmed to shut off the power supply when the workpiece reaches a preset target temperature.
Referring now to
In one embodiment of a method for repairing a coating on a steel workpiece using apparatus in accordance with the present disclosure, the procedure will typically include the following steps:
It will be readily appreciated by those skilled in the art that various alternative embodiments of the disclosed induction heating apparatus may be devised without departing from the scope of the present teachings, including modifications that may use equivalent structures or materials subsequently conceived or developed. It is to be especially understood that it is not intended for apparatus in accordance with the present disclosure to be limited to any particular described or illustrated embodiment, and that the substitution of a variant of a claimed or disclosed element or feature, without any substantial resultant change in the working of the apparatus, will not constitute a departure from the scope of the disclosure.
In this patent document, any form of the word “comprise” is to be understood in its non-limiting sense to mean that any item following such word is included, but items not expressly mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one such element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of the words “connect”, “engage”, or any other term describing an interaction between elements is not intended to limit that interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure.
Wherever used in this document, the terms “typical” and “typically” are to be interpreted in the sense of being representative of common usage or practice, and are not to be understood as implying invariability or essentiality.
Number | Date | Country | |
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62543231 | Aug 2017 | US |