EP0156545A2 - Heat treatment with an autoregulating heater - Google Patents
Heat treatment with an autoregulating heater Download PDFInfo
- Publication number
- EP0156545A2 EP0156545A2 EP85301501A EP85301501A EP0156545A2 EP 0156545 A2 EP0156545 A2 EP 0156545A2 EP 85301501 A EP85301501 A EP 85301501A EP 85301501 A EP85301501 A EP 85301501A EP 0156545 A2 EP0156545 A2 EP 0156545A2
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- EP
- European Patent Office
- Prior art keywords
- article
- temperature
- layer
- magnetic material
- heat
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 35
- 239000000696 magnetic material Substances 0.000 claims abstract description 33
- 238000000034 method Methods 0.000 claims abstract description 32
- 230000008569 process Effects 0.000 claims abstract description 30
- 230000035699 permeability Effects 0.000 claims abstract description 18
- 229910052751 metal Inorganic materials 0.000 claims abstract description 15
- 239000002184 metal Substances 0.000 claims abstract description 15
- 230000001105 regulatory effect Effects 0.000 claims abstract description 5
- 238000005496 tempering Methods 0.000 claims description 9
- 229910045601 alloy Inorganic materials 0.000 claims description 8
- 239000000956 alloy Substances 0.000 claims description 8
- 238000000137 annealing Methods 0.000 claims description 8
- 238000011065 in-situ storage Methods 0.000 claims description 6
- DMFGNRRURHSENX-UHFFFAOYSA-N beryllium copper Chemical compound [Be].[Cu] DMFGNRRURHSENX-UHFFFAOYSA-N 0.000 claims description 4
- 238000005121 nitriding Methods 0.000 claims description 4
- 230000008878 coupling Effects 0.000 claims description 3
- 238000010168 coupling process Methods 0.000 claims description 3
- 238000005859 coupling reaction Methods 0.000 claims description 3
- 239000000463 material Substances 0.000 claims description 3
- 229910001092 metal group alloy Inorganic materials 0.000 claims description 3
- 229910000881 Cu alloy Inorganic materials 0.000 claims 1
- 241000695274 Processa Species 0.000 claims 1
- 238000007493 shaping process Methods 0.000 claims 1
- 230000010455 autoregulation Effects 0.000 abstract description 34
- 230000000694 effects Effects 0.000 abstract description 4
- 229910000831 Steel Inorganic materials 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- 229910001004 magnetic alloy Inorganic materials 0.000 description 4
- 230000033228 biological regulation Effects 0.000 description 3
- 230000002411 adverse Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 230000020169 heat generation Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 206010073306 Exposure to radiation Diseases 0.000 description 1
- 229910000861 Mg alloy Inorganic materials 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000004320 controlled atmosphere Methods 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000011010 flushing procedure Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 230000008439 repair process Effects 0.000 description 1
- 230000007480 spreading Effects 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000007669 thermal treatment Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D11/00—Process control or regulation for heat treatments
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/34—Methods of heating
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
Definitions
- heat treatment In the field of metallurgy, heat treatment is employed to achieve numerous results. In a broad sense heat treatment includes any thermal treatment intended to control properties. With respect to metal alloys, such as steel, tempering and annealing are particularly well known methods of heat treatment.
- Heat treating to achieve a desired alteration of properties is often times a process that is performed optimally at a specific temperature.
- temperature chambers and complex heater/thermostat arrangements are generally employed.
- heat treating is performed before an article is sent to the field--the properties of the article being defined at the mill,factory, or other producing facility.
- it may be deemed desirable to effectuate changes in the metallurgical properties of the article in the field, or in situ, without the need for a temperature chamber, oven or heater-thermostat arrangement.
- an article of metal can be heat treated to effectuate property changes therein in the field by an autoregulating heater.
- the autoregulating heater is disposed along the portions of the article to be heat treated, thereby achieving the object of local heat treating.
- the autoregulating heater includes at least a first magnetic material which changes sharply in skin depth between temperatures below and above an autoregulating temperature (AR).
- AR autoregulating temperature
- the AR temperature is closely related to and determined by the Curie temperature.
- the changing skin depth results in corresponding variations in the level of heat produced in response to an a.c. current being applied to the first magnetic material.
- the heat generated is inversely related to the temperature of the heater. The inverse relationship between the temperature of the heater and the heat generated thereby renders the heater autoregulating or self-regulating so that a controlled application of heating can be effected to heat treat a metal article in the field to a temperature determined by an autoregulating heater.
- a.c.current flows primarily through a shallow depth of the magnetic layer below the AR temperature and into the low resistance non-magnetic layer above the.AR temperature, thereby greatly reducing heat generation at temperatures above theAR temperature.
- Autoregulation at a temperature substantially corresponding to the desired heat treatment temperature is achieved at generally several degrees less than the Curie point of the magnetic layer.
- a shielding effect is achieved for applications-in which the generation of signals outside the heater is not desired.
- a plurality of magnetic layers are provided in an autoregulating heater that is disposed along and transfers heat to an article in the field that is to be heat treated.
- an article may be heat treated at any of several temperatures.
- heat treating such as tempering
- Interposing a low resistance non-magnetic layer between and in contact with two magnetic layers may also be employed in the autoregulating heater to enable selectable temperature regulation in heat treating an article in the field.
- any one of the autoregulating heaters set ⁇ forth above into the article or portion thereof that is to be heat treated.
- the article-heater may be installed and, as required, the heater may be actuated by connecting a.c. current thereto to effectuate heat treatment in the field.
- the heater may be fixedly imbedded in the article or may, alternatively, be integrally formed along the article.
- the_pipe itself may comprise a magnetic layer of the autoregulating heater.
- the invention contemplates relieving stress in articles or portions thereof which have been over-hardened in the field or which have been rendered brittle due to exposure to radiation or which have been heavily work hardened due to machining or which have undergone fatigue cycling while in the field which might lead to fracture or failure.
- the invention contemplates heat treating tooled steel in the field and surface treating an article by nitriding or carborizing at a proper heat treating temperature.
- a metal pipe section 100 is shown coupled between two other pipe sections 102 and 104.
- the pipe section 100 is located along a pipeline 106 which, preferably, carries a fluid-such as oil or gas.
- a fluid-such as oil or gas When so employed, the pipe section 100 is often times exposed to numerous conditions that may adversely affect the structure and properties thereof. For example, thermal changes may result in stressing the pipe section 100.
- welds along the pipe section 100 may require stress relief after field welding.
- an autoregulating heater 110 for heat treating the pipe section 100 in the field (in situ) is provided. In this regard, it must be realized that accurate heat treating control is important to avoid overheating or underheating which seriously detracts from the heat treatment.
- the autoregulating heater 110 may be of various forms-- in each case the autoregulating heater 110 (a) being disposed along the pipe section 100 (or other workpiece) in the field along a length that is to be heat treated and (b) regulating at a temperature appropriate to heat treat the section 100 in the field.
- the autoregulating heater 100 is of a nature which permits the maintaining of a uniform temperature locally along the length L of the pipe section 100 to be heat treated.
- an a.c. current source 112 is shown.
- the source 112 provides a "constant" current which, preferably, is at a selected fixed frequency.
- the current is applied to enable the current to flow through a heating structure 114.
- heating structure 114 Several embodiments of heating structure 114 are illustrated in Figures II and III.
- the pipe section 200 is shown encompassed by a single magnetic layer 202.
- the magnetic layer 202 has a clamp member 204 which enables the magnetic layer 202 to be wrapped and held around the pipe section 200 in the field.
- the magnetic layer 202 has a prescribed resistivity ( ⁇ ) and a permeability ( ⁇ ) which varies sharply--at points above and. below an autoregulation (AR) temperature.
- the AR temperature is typically a few degrees lower than the conventionally defined-- Curie temperature of the magnetic layer 200.
- a sample table of magnetic materials is set forth below.
- the permeability (. ⁇ ) of the magnetic layer 202 corresponds substantially to the effective permeability well below the AR temperature and approximately one above the AR temperature.
- This variation in permeability changes the skin depth which is proportional to That is, as temperature increases to above the AR temperature, the permeability falls to one from, for example, 400 which results in the skin depth increasing by a factor of 20.
- the increase in skin depth results in an increase in the cross-section through which a.c. current is primarily confined.
- a.c. current distribution relative to depth in a magnetic material is an exponential function, namely current falls off at the rate of 1-e tt /S.D. where t is thickness and S.D. is skin depth.
- a.c. current is applied to the magnetic layer 202 the current is confined to a shallow depth about the outer periphery thereof when the temperature of the imagnetic layer 202 is below the AR temperature thereof. As the temperature increases and exceeds the AR temperature, the skin depth spreads to deeper thicknesses and current thereby flows through a larger cross-section. The heat generated is thereby reduced.
- the magnetic layer 202 is thermally conductive, the heat generated thereby when the skin depth is shallow is transferred to the pipe section 200. Moreover, since each portion of the magnetic layer 202 generates heat in response to its temperature, the heat is distributed so that greater heat is supplied to colder areas and less heat is supplied to warmer areas. Thus, heat from the magnetic layer 202 serves to raise the temperature of the length L (see Figure I) to a uniform level. In accordance with the invention as embodied in Figure II, the uniform level substantially corresponds to the AR temperature of the magnetic layer 202 and the temperature at which the desired heat treatment of the length L is effectuated.
- the AR temperature of the first magnetic layer 202 is selectable to correspond to the tempering temperature or the annealing temperature of the pipe section 100.
- autoregulation temperatures--near the Curie points-- as high as 1120°C are readily achievable by proper selection of magnetic alloy far the magnetic layer 202.
- the heat treatment of steel.and other metals (e.g. alloys) from which the pipe section 100 can be made is typically performed at temperatures below the autoregulation upper limits. Accordingly, the proper selection of an alloy wherein AR temperature substantially corresponds to the desired heat treatment temperature can be made.
- the source 112 may be selectively switched on and off to provide the desired heat treatment period.
- the heater or heater/article may have plug-or contact elements to which the source 112 can be selectively connected or disconnected as desired.
- the source 112 is connected to the pipe section 100 and the magnetic layer 110.
- the pipe section 100 may be a low resistance non-magnetic material.
- the resistance R thereby drops sharply and little I 2 R heat is produced.
- a circuit (not shown) may be provided to protect the source 112.
- the magnetic layer 110 it is noted; has a thickness defined to enable current to spread into pipe section 100 when temperatures rise above the Curie temperature.
- the magnetic layer is 1.0 to 1.8 skin depths (at the effective permeability) in thickness although other thicknesses may be employed.
- the source 112 would be connected directly across the magnetic layer.110 which, as desired, may include coupling elements (not shown) for receiving leads from the source 112.
- pipe section 300 is encircled by a heater 301 that includes a low resistance layer 302 (e.g. copper) which is encircled by magnetic layer 304.
- the layers 302 and 304 are in contact with each other and are each thermally conductive.
- An a.c. current is applied to the heater 301, the current being primarily confined to a shallow depth below the AR temperature and the current spreading to'flow along the low resistance path above the AR temperature.
- the pipe section 300 has heat supplied thereto by the autoregulating heater 301,
- Figure IV shows the connection of substantially constant a.c. current to an autoregulating heater 400 which is similar to heater 301.
- a source 402 supplies a.c. current which is initially confined to the outer skin of an outer magnetic layer 404.
- the inner layer 406 comprises a low resistance, non-magnetic layer 406 which encompasses a solid article 408--such as a pipe, strut, girder, or the like.
- a.c. current penetrates into the low resistance layer 406 resulting in a decrease in generated heat. That is, as is known in the art, the a.c.
- the a.c. current flows mainly along the outer surface of layer 404--the surface adjacent the circuit loop--when the temperature is below the AR temperature.
- the a.c. current spreads through the layer 404, which preferably has. a thickness of several skin depths when the layer 406 is at its effective permeability, and into the layer 406 resulting in less I 2 R heat.
- a connection of a.c. to the embodiment of Figure II may be made in a manner similar to that shown in Figure aV.
- the heater of Figure I I may also encircle a solid article--rather than the hollow article shown therein-to achieve the heat treatment thereof.
- Such heat treatment includes tempering, annealing, strengthening, increasing ductility, relieving stress, or otherwise affecting the metallurgical properties of a metal member.
- the heat treatment may be effected during assembly, repair or servicing of the metal member to obtain, retain, or regain desired properties.
- a spring 500 comprises a Beryllium-copper layer 502 and a magnetic alloy layer 504.
- the Beryllium-copper layer 502 in.a soft and ductile condition may be formed and fit to be placed in a desired location.
- the magnetic alloy layer 504 has a.c. current supplied thereto by a source 506--which results in the heater 500 initially increasing in temperature.
- the temperature is regulated at the Curie temperature of the layer 504.
- the regulated temperature substantially corresponds to the temperature at which the Beryllium-copper layer 502 hardens to a strong, spring-temper condition.
- This. heat treating is preferably conducted for several minutes at about 400°C.
- Other alloys, such as ..aluminum and magnesium alloys may also be hardened by such short, low temperature treating. Due to their high inherent conductivity, fabricating such alloys into the heater is contemplated by the invention.
- alloys may soften if heated too hot or too long. Accordingly, the invention contemplates softening as well in situ.
- a power cable 600 is terminated at a terminal bus 602 by a clamp ring 604.
- the ring 604 is initially soft to crimp and conform well to form the termination.
- the ring 604 comprises a magnetic alloy (see table above) which has an a.c. current applied thereto.
- the ring 604 autoregulates at the AR temperature thereof and hardens to achieve the desired end-use functionality.
- the crimp 604 represents both the article to be heat treated and the heater.
- the invention described therein is not limited to embodiments in which a heater is wrapped around an article in the field.
- the invention also extends to embodiments wherein the heater and article are incorporated as a single structure. That is, the article to be heated may itself comprise a magnetic material which autoregulates its own temperature.
- the article may include plural layer embodiments where, for example, a pipe as in Figure I, may include a magnetic layer and a non-magnetic layer concentric and disposed against,the magnetic layer. Such an embodiment operates like the layers 302 and 304 of Figure III.
- the pipe may comprise two magnetic layers with a non-magnetic layer interposed therebetween.
- FIG. VII shows a three layer pipe 700 including two concentric magnetic layers 702, 704 with a non-magnetic layer 706 therebetween.
- a "constant" a.c. source 708 is switchably connectable so that current flows along either the outer surface or inner surface of the pipe 700 when below the AR temperature of layer 702 or of layer 704 respectively.
- the pipe 700 comprises both the article to be heat treated and the heater disposed to effect the heat treatment.
- heat treatment may be performed repeatedly as required by simply connecting the a.c. source and applying current to the heater.
- the invention contemplates heating a metal by any of the various mechanisms discussed above and flushing the heated metal in the field with a gas to effectuate nitriding or carborizing .
- Carborizing and nitriding are known forms of surface-treating which, in accordance with the invention, are performed in the field, when the article is at the autoregulated temperature.
- insulation and circuit protection may be included in the various embodiments by one of skill in the art.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Physics & Mathematics (AREA)
- Heat Treatment Of Articles (AREA)
- General Induction Heating (AREA)
- Soft Magnetic Materials (AREA)
- Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
- Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
- Processing Of Meat And Fish (AREA)
- Control Of Heat Treatment Processes (AREA)
Abstract
Description
- In the field of metallurgy, heat treatment is employed to achieve numerous results. In a broad sense heat treatment includes any thermal treatment intended to control properties. With respect to metal alloys, such as steel, tempering and annealing are particularly well known methods of heat treatment.
- Heat treating to achieve a desired alteration of properties is often times a process that is performed optimally at a specific temperature. In order to maintain . control over temperature during such heat treatment, temperature chambers and complex heater/thermostat arrangements are generally employed.
- Typically, heat treating is performed before an article is sent to the field--the properties of the article being defined at the mill,factory, or other producing facility. However, at the time of installation of the article or after the article has been in use for a period of time, it may be deemed desirable to effectuate changes in the metallurgical properties of the article in the field, or in situ, without the need for a temperature chamber, oven or heater-thermostat arrangement. For example, where a pipe section along a pipeline is subject to cold temperatures and attendant degradation of properties, it is often desirable to service the pipe section by heat treatment in the field without the need for removing the section, similarly, when stress, fatigue, or temperature adversely affect a section of pipe along a pipeline or a strut along a bridge or the like, heat treatment in the field is often desirable. In addition, steels exposed to heavy neutron irradiation are generally embrittled.
- In these and other situations, it is often found that only portions of an article require heat treatment and that, in fact, the heat treatment should be confined to only those portions and that those portions be heated to a uniform temperature. That is, it may be that only part of an article is to be hardened, softened, strengthened, stress-relieved, tempered, annealed, or otherwise treated - in which case it is desired that heat treating be localized.
- In accordance with the invention, apparatus and process are provided wherein an article of metal can be heat treated to effectuate property changes therein in the field by an autoregulating heater. The autoregulating heater is disposed along the portions of the article to be heat treated, thereby achieving the object of local heat treating.
- Moreover, the autoregulating heater includes at least a first magnetic material which changes sharply in skin depth between temperatures below and above an autoregulating temperature (AR). The AR temperature is closely related to and determined by the Curie temperature. The changing skin depth results in corresponding variations in the level of heat produced in response to an a.c. current being applied to the first magnetic material. Accordingly, as discussed in U.S. Patent '4,256,945 to Carter and Krumme, and entitled "AUTOREGULATING HEATER", the heat generated is inversely related to the temperature of the heater. The inverse relationship between the temperature of the heater and the heat generated thereby renders the heater autoregulating or self-regulating so that a controlled application of heating can be effected to heat treat a metal article in the field to a temperature determined by an autoregulating heater.
- Furthermore, it is an object of the invention to generate autoregulating heat in at least one magnetic layer of an autoregulating heater, wherein the magnetic layer has an AR temperature substantially corresponding to the temperature at which heat treatment--such as tempering or annealing--is to be conducted.
- It is yet another object to provide an autoregulating heater along an article to be heat treated, wherein the heater has at least two thermally conductive layers--one comprising a magnetic layer and another comprising a low resistance nonmagnetic layer--wherein the magnetic layer has an AR temperature which substantially correspond to the desired temperature for heat treatment of the article. According to this embodiment, a.c.current flows primarily through a shallow depth of the magnetic layer below the AR temperature and into the low resistance non-magnetic layer above the.AR temperature, thereby greatly reducing heat generation at temperatures above theAR temperature. Autoregulation at a temperature substantially corresponding to the desired heat treatment temperature is achieved at generally several degrees less than the Curie point of the magnetic layer. Moreover, by properly defining the thickness of the low resistance non-magnetic layer a shielding effect is achieved for applications-in which the generation of signals outside the heater is not desired.
- In a further embodiment, a plurality of magnetic layers are provided in an autoregulating heater that is disposed along and transfers heat to an article in the field that is to be heat treated. In accordance with this embodiment, regulation at different AR temperatures--corresponding to the different magnetic layers--can be achieved. In this way, an article may be heat treated at any of several temperatures. Where heat treating, such as tempering, may include a plurality of stages--each characterized by given temperature and time specifications--this embodiment enables selected regulation: at selectable temperatures. Interposing a low resistance non-magnetic layer between and in contact with two magnetic layers may also be employed in the autoregulating heater to enable selectable temperature regulation in heat treating an article in the field.
- It is yet another object of the invention to incorporate any one of the autoregulating heaters set ― forth above into the article or portion thereof that is to be heat treated. The article-heater may be installed and, as required, the heater may be actuated by connecting a.c. current thereto to effectuate heat treatment in the field. In this regard, the heater may be fixedly imbedded in the article or may, alternatively, be integrally formed along the article. In the case of a steel pipe for example, the_pipe itself may comprise a magnetic layer of the autoregulating heater.
- It is still yet another object of the invention to provide a process whereby an autoregulating heater may be wrapped about a selected portion of a metal article in the field and the heater autoregulates at a corresponding AR temperature of a magnetic layer thereof--the magnetic layer being selected to have an AR temperature substantially corresponding to the desired heat treating temnerature.
- It is thus a major object of the invention to provide efficient, practical heat treatment without requiring an oven furnace, or complex heater/thermostat in a controlled atmosphere and heat treatment that is conveniently performed in the field.
- Finally, it is an object of the invention to provide autoregulated heating of an article to obtain, retain, and/or regain desired metallurgical properties therein by heat treating to harden, soften, relieve stress, temper, anneal, strengthen, or otherwise render the metallurgical properties of the article more appropriate for its function or end use. For example, the invention contemplates relieving stress in articles or portions thereof which have been over-hardened in the field or which have been rendered brittle due to exposure to radiation or which have been heavily work hardened due to machining or which have undergone fatigue cycling while in the field which might lead to fracture or failure. Also, the invention contemplates heat treating tooled steel in the field and surface treating an article by nitriding or carborizing at a proper heat treating temperature.
- Techniques according to the invention will now be described by way of example and with reference to the accampanying drawings in which:-
- Figure I is an illustration of pipe being heat treated in situ by an autoregulating heater in accordance with the invention.
- Figures II and III are cross-section views of two alternative types of autoregulating heaters.
- Figure IV is a front perspective view of an embodiment of the invention that is illustrated in Figure III.
- Figure V is a view illustrating an embodiment of the invention wherein a spring is heat treated.
- Figure VI is an illustration of an autoregulating heater and article to be heat treated integrally incorporated into a single crimp element.
- Figure VII is a front perspective view of a three-layer pipe which is both the article to be heat treated and an autoregulating heater which selectively controls the temperature of heat treatment.
- Referring to Figure I, a
metal pipe section 100 is shown coupled between twoother pipe sections 102 and 104. Thepipe section 100 is located along apipeline 106 which, preferably, carries a fluid-such as oil or gas. When so employed, thepipe section 100 is often times exposed to numerous conditions that may adversely affect the structure and properties thereof. For example, thermal changes may result in stressing thepipe section 100. In addition, welds along thepipe section 100 may require stress relief after field welding. To relieve such stress or otherwise enhance the metallurgical properties of thepipe section 100, an autoregulating heater 110 for heat treating thepipe section 100 in the field (in situ) is provided. In this regard, it must be realized that accurate heat treating control is important to avoid overheating or underheating which seriously detracts from the heat treatment. As discussed below, the autoregulating heater 110 may be of various forms-- in each case the autoregulating heater 110 (a) being disposed along the pipe section 100 (or other workpiece) in the field along a length that is to be heat treated and (b) regulating at a temperature appropriate to heat treat thesection 100 in the field. Moreover, theautoregulating heater 100 is of a nature which permits the maintaining of a uniform temperature locally along the length L of thepipe section 100 to be heat treated. - Referring still to Figure'I, an a.c.
current source 112 is shown. Thesource 112 provides a "constant" current which, preferably, is at a selected fixed frequency. The current is applied to enable the current to flow through a heating structure 114. - Several embodiments of heating structure 114 are illustrated in Figures II and III. In Figure II, the
pipe section 200 is shown encompassed by a singlemagnetic layer 202. Themagnetic layer 202 has aclamp member 204 which enables themagnetic layer 202 to be wrapped and held around thepipe section 200 in the field. Themagnetic layer 202 has a prescribed resistivity (ρ) and a permeability (µ) which varies sharply--at points above and. below an autoregulation (AR) temperature. The AR temperature is typically a few degrees lower than the conventionally defined-- Curie temperature of the magnetic layer 200.A sample table of magnetic materials is set forth below.magnetic layer 202 corresponds substantially to the effective permeability well below the AR temperature and approximately one above the AR temperature. This variation in permeability changes the skin depth which is proportional tomagnetic layer 202 increases above the AR temperature, the I2R heat generated drops. Conversely, as the temperature drops below the AR temperature,the I2R heat increases in accordance with skin depth changes. This effect is what characterizes a heater as autoregulating or self-regulating. -
- Still referring to Figure II, it is noted then that as "constant" a.c. current is applied to the
magnetic layer 202 the current is confined to a shallow depth about the outer periphery thereof when the temperature of theimagnetic layer 202 is below the AR temperature thereof. As the temperature increases and exceeds the AR temperature, the skin depth spreads to deeper thicknesses and current thereby flows through a larger cross-section. The heat generated is thereby reduced. - ) In that the
magnetic layer 202 is thermally conductive, the heat generated thereby when the skin depth is shallow is transferred to thepipe section 200. Moreover, since each portion of themagnetic layer 202 generates heat in response to its temperature, the heat is distributed so that greater heat is supplied to colder areas and less heat is supplied to warmer areas. Thus, heat from themagnetic layer 202 serves to raise the temperature of the length L (see Figure I) to a uniform level. In accordance with the invention as embodied in Figure II, the uniform level substantially corresponds to the AR temperature of themagnetic layer 202 and the temperature at which the desired heat treatment of the length L is effectuated. - Specifically, the AR temperature of the first
magnetic layer 202 is selectable to correspond to the tempering temperature or the annealing temperature of thepipe section 100. In this regard it is noted that autoregulation temperatures--near the Curie points-- as high as 1120°C (the Curie temperature of Cobalt) are readily achievable by proper selection of magnetic alloy far themagnetic layer 202. - The heat treatment of steel.and other metals (e.g. alloys) from which the
pipe section 100 can be made is typically performed at temperatures below the autoregulation upper limits. Accordingly, the proper selection of an alloy wherein AR temperature substantially corresponds to the desired heat treatment temperature can be made. - Where heat treating is normally conducted for a given period of time, it is further noted that the
source 112 may be selectively switched on and off to provide the desired heat treatment period. Alternatively, the heater (or heater/article) may have plug-or contact elements to which thesource 112 can be selectively connected or disconnected as desired. - Referring again to Figure I, it is observed that the
source 112 is connected to thepipe section 100 and the magnetic layer 110. In this embodiment thepipe section 100 may be a low resistance non-magnetic material. As the skin depth of the magnetic layer 110 increases, current will eventually spread to thepipe section 100. The resistance R thereby drops sharply and little I2 R heat is produced. If needed, a circuit (not shown) may be provided to protect thesource 112. The magnetic layer 110, it is noted; has a thickness defined to enable current to spread intopipe section 100 when temperatures rise above the Curie temperature. Preferably the magnetic layer is 1.0 to 1.8 skin depths (at the effective permeability) in thickness although other thicknesses may be employed. - Still referring to Figure I, if the
pipe section 100 is not of a low resistance material, thesource 112 would be connected directly across the magnetic layer.110 which, as desired, may include coupling elements (not shown) for receiving leads from thesource 112. - Turning now to Figure III,
pipe section 300 is encircled by a heater 301 that includes a low resistance layer 302 (e.g. copper) which is encircled by magnetic layer 304.Thelayers pipe section 300 has heat supplied thereto by the autoregulating heater 301, - Figure IV shows the connection of substantially constant a.c. current to an
autoregulating heater 400 which is similar to heater 301. Asource 402 supplies a.c. current which is initially confined to the outer skin of an outermagnetic layer 404. Theinner layer 406 comprises a low resistance,non-magnetic layer 406 which encompasses asolid article 408--such as a pipe, strut, girder, or the like. When themagnetic layer 404 is below its AR temperature--which is typically several degrees below the Curie point--considerable heat is generated therein. As the temperature climbs to the AR temperature, a.c. current penetrates into thelow resistance layer 406 resulting in a decrease in generated heat. That is, as is known in the art, the a.c. current flows mainly along the outer surface oflayer 404--the surface adjacent the circuit loop--when the temperature is below the AR temperature. When the temperature reaches the AR temperature, the a.c. current spreads through thelayer 404, which preferably has. a thickness of several skin depths when thelayer 406 is at its effective permeability, and into thelayer 406 resulting in less I2R heat. - A connection of a.c. to the embodiment of Figure II may be made in a manner similar to that shown in Figure aV. Moreover, the heater of Figure II may also encircle a solid article--rather than the hollow article shown therein-to achieve the heat treatment thereof. Such heat treatment includes tempering, annealing, strengthening, increasing ductility, relieving stress, or otherwise affecting the metallurgical properties of a metal member. The heat treatment may be effected during assembly, repair or servicing of the metal member to obtain, retain, or regain desired properties.
- Referring now to Figure V, a
spring 500 comprises a Beryllium-copper layer 502 and amagnetic alloy layer 504. The Beryllium-copper layer 502 in.a soft and ductile condition may be formed and fit to be placed in a desired location. After placement, themagnetic alloy layer 504 has a.c. current supplied thereto by asource 506--which results in theheater 500 initially increasing in temperature. The temperature is regulated at the Curie temperature of thelayer 504. The regulated temperature substantially corresponds to the temperature at which the Beryllium-copper layer 502 hardens to a strong, spring-temper condition. This. heat treating is preferably conducted for several minutes at about 400°C. Other alloys, such as ..aluminum and magnesium alloys may also be hardened by such short, low temperature treating. Due to their high inherent conductivity, fabricating such alloys into the heater is contemplated by the invention. - In addition to hardening, it is noted that alloys may soften if heated too hot or too long. Accordingly, the invention contemplates softening as well in situ.
- Referring next to Figure VI, a
power cable 600 is terminated at aterminal bus 602 by aclamp ring 604. Thering 604 is initially soft to crimp and conform well to form the termination. Thering 604 comprises a magnetic alloy (see table above) which has an a.c. current applied thereto. Thering 604 autoregulates at the AR temperature thereof and hardens to achieve the desired end-use functionality. Thecrimp 604 represents both the article to be heat treated and the heater. - In reviewing Figures I through IV, it should be noted that the invention described therein is not limited to embodiments in which a heater is wrapped around an article in the field. The invention also extends to embodiments wherein the heater and article are incorporated as a single structure. That is, the article to be heated may itself comprise a magnetic material which autoregulates its own temperature. Moreover, the article may include plural layer embodiments where, for example, a pipe as in Figure I, may include a magnetic layer and a non-magnetic layer concentric and disposed against,the magnetic layer. Such an embodiment operates like the
layers layers 404 through 408 of Figure IV, except that the heater -402 is not only disposed along but is also at least part of the article being heat treated. Figure VII shows a three layer pipe 700 including two concentricmagnetic layers 702, 704 with anon-magnetic layer 706 therebetween. A "constant" a.c.source 708 is switchably connectable so that current flows along either the outer surface or inner surface of the pipe 700 when below the AR temperature oflayer 702 or of layer 704 respectively. The pipe 700 comprises both the article to be heat treated and the heater disposed to effect the heat treatment. - In any of the embodiments, it is further noted, heat treatment may be performed repeatedly as required by simply connecting the a.c. source and applying current to the heater.
- Moreover, in yet another embodiment of heat treating in the field, the invention contemplates heating a metal by any of the various mechanisms discussed above and flushing the heated metal in the field with a gas to effectuate nitriding or carborizing.. Carborizing and nitriding are known forms of surface-treating which, in accordance with the invention, are performed in the field, when the article is at the autoregulated temperature.
- Given the above teachings, it is noted that insulation and circuit protection may be included in the various embodiments by one of skill in the art.
Claims (35)
wherein the uniting step is performed in the field and includes the step of positioning the heater in heat transfer relationship with the portion of the article to be heated.
selectively regulating the temperature of the heater and the article to the AR temperature of the first magnetic material or the AR temperature of the second magnetic material.
wherein the AR temperature of said first layer substantially corresponds to the annealing temperature of the portion of the article that is to be heat treated.
wherein the AR temperature of said first layer substantially corresponds to the heat tempering temperature of the portion of the article that is to be heat treated.
wherein said autoregulating heater comprises a strap which wraps around an annular band of the article and directs heat treating heat thereto.
wherein the AR temperature of said first layer substantially corresponds to a temperature at which the spring achieves enhanced strength properties.
wherein the AR temperature of said first layer substantially corresponds to a temperature at which brittleness of the alloy along the portion of the article to be heat treated is reduced and stress relief therein achieved.
wherein the AR temperature of said first layer substantially corresponds to a temperature whereat the alloy softens to enhance the ductility of the alloy along the portion of the article to be heat treated.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT85301501T ATE56476T1 (en) | 1984-03-06 | 1985-03-05 | HEAT TREATMENT PROCESS WITH SELF-REGULATORY HEATER. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US58671984A | 1984-03-06 | 1984-03-06 | |
US586719 | 1984-03-06 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0156545A2 true EP0156545A2 (en) | 1985-10-02 |
EP0156545A3 EP0156545A3 (en) | 1987-05-13 |
EP0156545B1 EP0156545B1 (en) | 1990-09-12 |
Family
ID=24346880
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP85301501A Expired - Lifetime EP0156545B1 (en) | 1984-03-06 | 1985-03-05 | Heat treatment with an autoregulating heater |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0156545B1 (en) |
JP (1) | JPH0656793B2 (en) |
AT (1) | ATE56476T1 (en) |
CA (1) | CA1265419A (en) |
DE (1) | DE3579605D1 (en) |
WO (1) | WO1985004069A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0250094A1 (en) * | 1986-06-10 | 1987-12-23 | Metcal Inc. | High power self-regulating heater |
EP0252719B1 (en) * | 1986-07-07 | 1992-11-11 | Chisso Engineering CO. LTD. | Electric fluid heater |
WO2012104004A1 (en) * | 2011-02-01 | 2012-08-09 | Rwe Technology Gmbh | Method for heat treating weld seams on power plant components |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4091813A (en) * | 1975-03-14 | 1978-05-30 | Robert F. Shaw | Surgical instrument having self-regulated electrical proximity heating of its cutting edge and method of using the same |
US4256945A (en) * | 1979-08-31 | 1981-03-17 | Iris Associates | Alternating current electrically resistive heating element having intrinsic temperature control |
WO1982003148A1 (en) * | 1981-03-02 | 1982-09-16 | Ass Iris | Electrically resistive heating element having temperature control |
WO1982003305A1 (en) * | 1981-03-16 | 1982-09-30 | Ass Iris | Shielded heating element having intrinsic temperature control |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
BE518744A (en) * | 1952-03-28 | |||
US4001054A (en) * | 1974-04-10 | 1977-01-04 | Makepeace Charles E | Process for making metal pipe |
US4229235A (en) * | 1977-10-25 | 1980-10-21 | Hitachi, Ltd. | Heat-treating method for pipes |
-
1985
- 1985-03-05 AT AT85301501T patent/ATE56476T1/en not_active IP Right Cessation
- 1985-03-05 EP EP85301501A patent/EP0156545B1/en not_active Expired - Lifetime
- 1985-03-05 DE DE8585301501T patent/DE3579605D1/en not_active Expired - Fee Related
- 1985-03-05 CA CA000475792A patent/CA1265419A/en not_active Expired - Fee Related
- 1985-03-06 WO PCT/US1985/000368 patent/WO1985004069A1/en unknown
- 1985-03-06 JP JP60501327A patent/JPH0656793B2/en not_active Expired - Lifetime
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4091813A (en) * | 1975-03-14 | 1978-05-30 | Robert F. Shaw | Surgical instrument having self-regulated electrical proximity heating of its cutting edge and method of using the same |
US4256945A (en) * | 1979-08-31 | 1981-03-17 | Iris Associates | Alternating current electrically resistive heating element having intrinsic temperature control |
WO1982003148A1 (en) * | 1981-03-02 | 1982-09-16 | Ass Iris | Electrically resistive heating element having temperature control |
WO1982003305A1 (en) * | 1981-03-16 | 1982-09-30 | Ass Iris | Shielded heating element having intrinsic temperature control |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0250094A1 (en) * | 1986-06-10 | 1987-12-23 | Metcal Inc. | High power self-regulating heater |
EP0252719B1 (en) * | 1986-07-07 | 1992-11-11 | Chisso Engineering CO. LTD. | Electric fluid heater |
WO2012104004A1 (en) * | 2011-02-01 | 2012-08-09 | Rwe Technology Gmbh | Method for heat treating weld seams on power plant components |
Also Published As
Publication number | Publication date |
---|---|
CA1265419A (en) | 1990-02-06 |
EP0156545B1 (en) | 1990-09-12 |
WO1985004069A1 (en) | 1985-09-12 |
EP0156545A3 (en) | 1987-05-13 |
JPH0656793B2 (en) | 1994-07-27 |
JPS61501355A (en) | 1986-07-03 |
DE3579605D1 (en) | 1990-10-18 |
ATE56476T1 (en) | 1990-09-15 |
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