EP0156545B1 - Heat treatment with an autoregulating heater - Google Patents
Heat treatment with an autoregulating heater Download PDFInfo
- Publication number
- EP0156545B1 EP0156545B1 EP85301501A EP85301501A EP0156545B1 EP 0156545 B1 EP0156545 B1 EP 0156545B1 EP 85301501 A EP85301501 A EP 85301501A EP 85301501 A EP85301501 A EP 85301501A EP 0156545 B1 EP0156545 B1 EP 0156545B1
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- European Patent Office
- Prior art keywords
- article
- heat
- temperature
- magnetic material
- layer
- 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.)
- Expired - Lifetime
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 49
- 239000000696 magnetic material Substances 0.000 claims abstract description 23
- 238000000034 method Methods 0.000 claims abstract description 18
- 230000008569 process Effects 0.000 claims abstract description 16
- 229910052751 metal Inorganic materials 0.000 claims abstract description 11
- 239000002184 metal Substances 0.000 claims abstract description 11
- 230000035699 permeability Effects 0.000 claims abstract description 11
- 238000000137 annealing Methods 0.000 claims description 7
- 238000005496 tempering Methods 0.000 claims description 6
- 238000005255 carburizing Methods 0.000 claims description 4
- 238000005121 nitriding Methods 0.000 claims description 4
- 238000009434 installation Methods 0.000 claims description 3
- 239000000463 material Substances 0.000 claims description 3
- 238000004381 surface treatment Methods 0.000 claims 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims 1
- 229910052802 copper Inorganic materials 0.000 claims 1
- 239000010949 copper Substances 0.000 claims 1
- 230000010455 autoregulation Effects 0.000 abstract description 33
- 230000000694 effects Effects 0.000 abstract description 5
- 230000001105 regulatory effect Effects 0.000 abstract description 4
- 229910000831 Steel Inorganic materials 0.000 description 8
- 239000010959 steel Substances 0.000 description 8
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 238000011065 in-situ storage Methods 0.000 description 4
- DMFGNRRURHSENX-UHFFFAOYSA-N beryllium copper Chemical compound [Be].[Cu] DMFGNRRURHSENX-UHFFFAOYSA-N 0.000 description 3
- 230000033228 biological regulation Effects 0.000 description 3
- 229910001004 magnetic alloy Inorganic materials 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
- 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
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011010 flushing procedure 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
- 229910001092 metal group alloy Inorganic materials 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
- 230000004044 response Effects 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
- 230000007480 spreading Effects 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.
- 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.
- DE-A-1135586 there is disclosed a process for annealing a coated steel sheet in which an a.c. current is induced in the steel, thereby creating a Joule heating effect, and because the steel is a magnetic material having a Curie point autoregulation of the heat input can be achieved to sustain a temperature in the region of the Curie point.
- Such technology is of very limited application because it can only be employed when the temperature of autoregulation, which is of course determined by the nature of the steel, is high enough to achieve the required annealing. That is to say, if the Curie temperature lies below the temperature that must be reached to achieve the desired heat treatment the process fails.
- a process for altering the metallurgical properties of a metal article by a heat treatment characterised by the steps of: selecting a magnetic material having a Curie temperature that lies in the temperature region of the heat treatment to be applied to the article and which has a magnetic permeability which greatly exceeds 1 at temperatures below said Curie temperature, placing a layer of said magnetic material in thermal interchange relationship with said article, and passing an a.c.
- 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.
- an autoregulating heater is provided 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 corresponds to the desired temperature for heat treatment of the article.
- 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 the AR 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 auto-regulating heater to enable selectable temperature regulation in heat treatment an article in the field.
- any one of the autoregulating heaters set forth above may be incorporated into the article or portion thereof that is to be heat treated.
- the article-heater combination may be installed and, as required, the heater may be actuated by connecting a.c. current thereto to effectuate heat treatment in the field.
- 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 temperature.
- the invention thus provides an 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.
- Such autoregulated heating of an article can be employed 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.
- 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 carburizing 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 (p) and a permeability (p) 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 (p) 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 ⁇ / ⁇ f. 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.
- 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 magnetic 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.
- 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.
- auto-regulation temperatures-near the Curie points-as high as 1120°C are readily achievable by proper selection of magnetic alloy for 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 auto-regulation 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 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 1 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 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 1 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 IV.
- 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.
- 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.
- Figure VI 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 thus comprises both the article to be heat treated and auto-regulating heaters disposed to effect 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 carburizing.
- Carburizing 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)
- Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
- Soft Magnetic Materials (AREA)
- Processing Of Meat And Fish (AREA)
- Processing And Handling Of Plastics And Other Materials For Molding In General (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 fieid, 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 DE-A-1135586 there is disclosed a process for annealing a coated steel sheet in which an a.c. current is induced in the steel, thereby creating a Joule heating effect, and because the steel is a magnetic material having a Curie point autoregulation of the heat input can be achieved to sustain a temperature in the region of the Curie point. However, such technology is of very limited application because it can only be employed when the temperature of autoregulation, which is of course determined by the nature of the steel, is high enough to achieve the required annealing. That is to say, if the Curie temperature lies below the temperature that must be reached to achieve the desired heat treatment the process fails.
- It is therefore an object of the present invention to overcome the very restricted nature of the prior process and provide a new solution which not only can be employed in the field after an article has been installed, and perhaps after extended use of that article, but also is not dependent on the Curie point of the material of the article.
- According to the present invention, there is provided a process for altering the metallurgical properties of a metal article by a heat treatment, such as hardening, annealing, tempering or stress-relieving, characterised by the steps of: selecting a magnetic material having a Curie temperature that lies in the temperature region of the heat treatment to be applied to the article and which has a magnetic permeability which greatly exceeds 1 at temperatures below said Curie temperature, placing a layer of said magnetic material in thermal interchange relationship with said article, and passing an a.c. current of substantially constant amplitude through said magnetic material layer sufficient to generate enough Joule heating to raise the temperature of said magnetic material to about its Curie temperature, thereby providing a heater that supplies the heat for said heat treatment and auto-regulates substantially at the correct temperature level for said heat treatment.
- 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.
- In one embodiment an autoregulating heater is provided 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 corresponds 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 the AR 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 auto-regulating heater to enable selectable temperature regulation in heat treatment an article in the field.
- Any one of the autoregulating heaters set forth above may be incorporated into the article or portion thereof that is to be heat treated. The article-heater combination may be installed and, as required, the heater may be actuated by connecting a.c. current thereto to effectuate heat treatment in the field.
- Alternatively, 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 temperature.
- The invention thus provides an 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.
- Such autoregulated heating of an article can be employed 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 carburizing at a proper heat treating temperature.
- Techniques according to the invention will now be described by way of example and with reference to the accompanying 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 a front perspective view of a three-layer pipe which comprises 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 aheating structure 114. - Several embodiments of
heating structure 114 are illustrated in Figures II and III. In Figure II, thepipe 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 (p) and a permeability (p) 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 themagnetic layer 200. A sample table of magnetic materials is set forth below. - As is well known, the permeability (p) 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 √ρ/µf. 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, in turn, results in an increase in the cross-section through which a.c. current is primarily confined. In this regard, it is noted that a.c. current distribution relative to depth in a magnetic material is an exponential function, namely current falls off at the rate of 1-ett/S.D. where t is thickness and S.D. is skin depth. Accordingly, 63.2% of the current is confined to one skin depth. That is, where 12R is the heat generated and where 12 is considered relatively "constant", changes in R primarily determine changes in heat generation. Hence, as the temperature of themagnetic layer 202 increases above the AR temperature, the 12R heat generated drops. Conversely, as the temperature drops below the AR temperature, the 12R 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 themagnetic 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 auto-regulation temperatures-near the Curie points-as high as 1120°C (the Curie temperature of Cobalt) are readily achievable by proper selection of magnetic alloy for 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 auto-regulation 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 may have plug or contact elements to which thesource 112 can be selectively connected or disconnected as desired. - Referring again to Figure 1, 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 12R 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 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 bymagnetic 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. The inner layer comprises a low resistance,non-magnetic layer 406 which encompasses a solid 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 of layer 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 12R heat. - A connection of a.c. to the embodiment of Figure II may be made in a manner similar to that shown in Figure IV. 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 a source 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.
- Figure VI shows a three layer pipe 700 including two concentric
magnetic layers 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 oflayer 704 respectively. The pipe 700 thus comprises both the article to be heat treated and auto-regulating heaters disposed to effect 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 carburizing. Carburizing 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 (10)
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 EP0156545A2 (en) | 1985-10-02 |
EP0156545A3 EP0156545A3 (en) | 1987-05-13 |
EP0156545B1 true 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) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4814587A (en) * | 1986-06-10 | 1989-03-21 | Metcal, Inc. | High power self-regulating heater |
JPH0760017B2 (en) * | 1986-07-07 | 1995-06-28 | チッソエンジニアリング株式会社 | Electric fluid heater |
DE102011009947A1 (en) * | 2011-02-01 | 2012-08-02 | Rwe Technology Gmbh | Process for the heat treatment of welds on power plant components |
Family Cites Families (7)
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 |
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 |
US4229235A (en) * | 1977-10-25 | 1980-10-21 | Hitachi, Ltd. | Heat-treating method for pipes |
US4701587A (en) * | 1979-08-31 | 1987-10-20 | Metcal, Inc. | Shielded heating element having intrinsic temperature control |
US4256945A (en) * | 1979-08-31 | 1981-03-17 | Iris Associates | Alternating current electrically resistive heating element having intrinsic temperature control |
DE3177193D1 (en) * | 1981-03-02 | 1990-07-19 | Metcal Inc | ELECTRIC RESISTANCE HEATING ELEMENT WITH TEMPERATURE CONTROL. |
-
1985
- 1985-03-05 CA CA000475792A patent/CA1265419A/en not_active Expired - Fee Related
- 1985-03-05 DE DE8585301501T patent/DE3579605D1/en not_active Expired - Fee Related
- 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
- 1985-03-06 WO PCT/US1985/000368 patent/WO1985004069A1/en unknown
- 1985-03-06 JP JP60501327A patent/JPH0656793B2/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
ATE56476T1 (en) | 1990-09-15 |
CA1265419A (en) | 1990-02-06 |
EP0156545A2 (en) | 1985-10-02 |
DE3579605D1 (en) | 1990-10-18 |
WO1985004069A1 (en) | 1985-09-12 |
JPH0656793B2 (en) | 1994-07-27 |
EP0156545A3 (en) | 1987-05-13 |
JPS61501355A (en) | 1986-07-03 |
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