CA1066783A - Method and apparatus for pipeline induction heating - Google Patents
Method and apparatus for pipeline induction heatingInfo
- Publication number
- CA1066783A CA1066783A CA242,851A CA242851A CA1066783A CA 1066783 A CA1066783 A CA 1066783A CA 242851 A CA242851 A CA 242851A CA 1066783 A CA1066783 A CA 1066783A
- Authority
- CA
- Canada
- Prior art keywords
- pipe
- weld
- heating
- jaws
- induction
- 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
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K13/00—Welding by high-frequency current heating
- B23K13/01—Welding by high-frequency current heating by induction heating
- B23K13/02—Seam welding
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Induction Heating (AREA)
- Heat Treatment Of Articles (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
For welding pipeline pipe in the low ambient temperatures, encountered in extreme latitudes that may range from + 32°F to - 70°F and possibly lower, the induction heating of the pipe in the area of the weld joint prior to welding and at selected other times such as while the weld is being made, during quenching and for normalizing. A split-ring pancake induction heater is used comprising a pair of separable jaws that may be opened for lateral application to the pipe and closed to circumferentially embrace the same and wherein each of the jaws constitutes a separate induc-tor. Unlike the welding difficulties that would be caused by a ring induc-tor, the split-ring nature of the present inductor tends to break up unwanted eddy currents giving improved weld disposition quality and production speed.
The unit is self-contained and readily movable along the pipe-line route.
This method of induction heating comprises the steps of preheating the pipe in the area of the weld joint and heating it while the weld is being made.
It provides also for further heating during the quenching and heating for normalizing.
For welding pipeline pipe in the low ambient temperatures, encountered in extreme latitudes that may range from + 32°F to - 70°F and possibly lower, the induction heating of the pipe in the area of the weld joint prior to welding and at selected other times such as while the weld is being made, during quenching and for normalizing. A split-ring pancake induction heater is used comprising a pair of separable jaws that may be opened for lateral application to the pipe and closed to circumferentially embrace the same and wherein each of the jaws constitutes a separate induc-tor. Unlike the welding difficulties that would be caused by a ring induc-tor, the split-ring nature of the present inductor tends to break up unwanted eddy currents giving improved weld disposition quality and production speed.
The unit is self-contained and readily movable along the pipe-line route.
This method of induction heating comprises the steps of preheating the pipe in the area of the weld joint and heating it while the weld is being made.
It provides also for further heating during the quenching and heating for normalizing.
Description
This invention relates to improvements in a method of pipe heating and apparatus therefor appertaining more particularly to the induction heating of adjacent areas when a length of pipe is being welded into a pipeline at low ambient temperature.
BACKGROUND OF THE INVENTION
It is known to heat-treat metal pipe and other tubular articles to strengthen the same and improve the metallur-gical formation thereof. In the course of welding successive lengths of pipe to a pipeline in northern latitudes a series of complex new problems has been encountered in consequence of the low ambient temperatures e.g. shock from the sudden heating of the frigid cold metal at the weld joint especially with high alloy steel resulting in the cracking of the metal, the formation of martensite or other undesirable metallurgical characteristics by the large mass of cold pipe quenching the weld, the need to re-tard or modulate the cooling and after-weld normalizing to obtain a finer grain size and eliminate internal stresses.
It is an object of the invention to provide a method of heating pipe as when welding lengths of pipe into a pipeline at low ambient temperatures comprising at least a plural-ity of the following steps of (a) preheating the areas of pipe adjacent the joint, tb) heating the pipe during the welding pro-cess and ~c) postheating to retard cooling and (d) for normaliz-` ing.
` 3 A further object of the invention is to provide a portable inductor heater moveable along a pipeline route.
A further object is to provide a split-ring pancake inductor readily applied about and removed from the weld area.
A still further object is to provide an induction heater in the form of a pair of openable semi-circular jaws design-ed to encircle the pipe in the weld joint area.
.
, ~ . . . . . . .
1(~66783 To the accomplishment of these and related objects as shall become apparent as the description proceeds, the invention resides in the method of heating pipe in low ambient temperatures and in the construction, combination and arrangement of parts of the portable induction heater as shall be hereinafter more fully described, illustrated in the accompanying drawings and pointed out in the claims hereunto appended.
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will be best understood and can be more clearly described when reference is had to the drawings forming a part of this disclosure wherein like characters indi-cate like parts throughout the several views.
In the drawings:
Figure 1 is a perspective view of a pipeline construction with the induction heater applied to the last weld; -~
Figure 2 is a line diagram of the portable in-duction heater;
Figure 3 is an enlarged isometric view of the split-ring pancake induction heater; --Figure 4 is a further enlarged elevation of the upper jaw of the induction heater as seen from the left side of Pigure 3;
Figure 5 is a hori~ontal section through the jaw, as taken on line 5-5 of Figure 4;
Figure 6 is a further enlarged end elevation of the inductor showing the jaws in closed position; and Figure 7 is a similar elevation showing the jaws in open position.
DETAILED-DESCRIPTION OF THE INVENTION:
THE METHOD:
In welding lengths of pipe into a pipeline in -the far north the quality of the weld and the pipe is affected by the low ambient temperature. I have found a method of overcom-ing this problem by heating the pipe ends in the weld joint area
BACKGROUND OF THE INVENTION
It is known to heat-treat metal pipe and other tubular articles to strengthen the same and improve the metallur-gical formation thereof. In the course of welding successive lengths of pipe to a pipeline in northern latitudes a series of complex new problems has been encountered in consequence of the low ambient temperatures e.g. shock from the sudden heating of the frigid cold metal at the weld joint especially with high alloy steel resulting in the cracking of the metal, the formation of martensite or other undesirable metallurgical characteristics by the large mass of cold pipe quenching the weld, the need to re-tard or modulate the cooling and after-weld normalizing to obtain a finer grain size and eliminate internal stresses.
It is an object of the invention to provide a method of heating pipe as when welding lengths of pipe into a pipeline at low ambient temperatures comprising at least a plural-ity of the following steps of (a) preheating the areas of pipe adjacent the joint, tb) heating the pipe during the welding pro-cess and ~c) postheating to retard cooling and (d) for normaliz-` ing.
` 3 A further object of the invention is to provide a portable inductor heater moveable along a pipeline route.
A further object is to provide a split-ring pancake inductor readily applied about and removed from the weld area.
A still further object is to provide an induction heater in the form of a pair of openable semi-circular jaws design-ed to encircle the pipe in the weld joint area.
.
, ~ . . . . . . .
1(~66783 To the accomplishment of these and related objects as shall become apparent as the description proceeds, the invention resides in the method of heating pipe in low ambient temperatures and in the construction, combination and arrangement of parts of the portable induction heater as shall be hereinafter more fully described, illustrated in the accompanying drawings and pointed out in the claims hereunto appended.
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will be best understood and can be more clearly described when reference is had to the drawings forming a part of this disclosure wherein like characters indi-cate like parts throughout the several views.
In the drawings:
Figure 1 is a perspective view of a pipeline construction with the induction heater applied to the last weld; -~
Figure 2 is a line diagram of the portable in-duction heater;
Figure 3 is an enlarged isometric view of the split-ring pancake induction heater; --Figure 4 is a further enlarged elevation of the upper jaw of the induction heater as seen from the left side of Pigure 3;
Figure 5 is a hori~ontal section through the jaw, as taken on line 5-5 of Figure 4;
Figure 6 is a further enlarged end elevation of the inductor showing the jaws in closed position; and Figure 7 is a similar elevation showing the jaws in open position.
DETAILED-DESCRIPTION OF THE INVENTION:
THE METHOD:
In welding lengths of pipe into a pipeline in -the far north the quality of the weld and the pipe is affected by the low ambient temperature. I have found a method of overcom-ing this problem by heating the pipe ends in the weld joint area
-2-1()66783 ~and have in~ented a specific piece of apparatus for applying the needed heat to the pipe by means of induction wherein the entire induction heating unit is self-contained and moveable along the pipeline route.
To obtain maximum results in welding under such conditions of low ambient temperature the circumference of the pipe for a distance of approximately four inches on each side of the weld joint should be preheated approximately one minute at a temperature within the range of approximately 250F to approximate-ly 650F.
To prevent the large mass of cold pipe fromquenching the weld as it is being made and to retard the cooling rate în the weld zone it is desirable and in some cases necessary to apply further heat. Following the welding the entire circumfer- -ential field can be normalized by induction heating to approximately ; 1550F and then cooling in air to produce a weld of finer grain size and avoid internal stresses.
In the present method the inductor is powered : by an induction generator in the range of a low frequency of approximately 60 cycles per second to a high frequency of approx-imately 450,000 cycles per second.
- In other aspects of ~ipe heating in low ambient temperatures the width of the circumferential band of the pipe, the temperature at which it should be heated and the duration of the heating period are varied.
Por example prior to bending the pipe it should be pr~eated for a length of approximately four feet for a period of ` four minutes and at a temperature of approximately 650F or within tho range of 500~ to 900F. While for painting and coating the weld ~oint the pipe should be heated for a length of approximately eight inches, the same as the weld p~eheat, for a period of approx-imately four minutes at a temperature of approximately 250F.
3_ 10~i6783 THE SPLIT-RING INDUCTOR:
.
It is common practice in mills manufacturing steel pipe to use a standard inductor for normalizing pipe, the long weld seam being normalized by a bar inductor while the body of the pipe is heated by a ring inductor. For preheating pipe being welded into a pipeline under low ambient temperature and for operating in the field alongside a pipeline route, a pancake split-ring inductor is employed that allows it to be applied laterally to and removed from the pipe and in addition the split-ring nature of the inductor breaks up eddy currents that form when a ring inductor is used~ such currents causing welding difficulties by affecting the weld disposition quality and pro-duction speed.
In the drawings, Figure 1 shows a welded pipe-line 1 with the unfinished end resting on a support skid 2 and a length of pipe 3 about to be welded into the pipeline is placed in end to end relation adjacent to and in alignment therewith, such pipe 3 being carried by a side boom tractor or crane. A
heater in the form of a split-ring pancake inductor 4 loosely en-circles the joint to be welded, overlying approximately four inches of each of the confronting pipes.
A portable unit is seen in the line diagram of Figure 2 designed to be supported on a suitable carrier that is -- moveable alongside a pipeline being constructed. Such a unit would include a diesel motor or other prime mover 5 driving an alternator generator 6 supplying power to control cabinet 7 and via flexible cables 8 to the inductor 4.
The split-ring inductor 4, Figures 3-7 inclusive, serviced from the control cabinet 7 by cables 8 may be mounted ;~ .
~30 on the same or a separate carrier such as a tractor or the like by means of its support structure 9 here shown as a vertical - -channel iron frame. Prom opposite sides of the frame a,longitud--4^
~ , , , . .. : , ~ . , ~ 0 6 67 8 3 inally spaced pair of parallel arms 10 project horizontally to carry the hinge pin 11 on which a pair of complementary semi-circular split-ring inductor jaws 12 and 13 pivot. The inductor 4 includes these two hingedly connected semi-circular jaws 12 and 13 to allow the inductor to be opened, applied laterally to a pipe and then closed to circumferentially embrace the pipe.
Each inductor jaw 12 and 13 hingedly mounted on the pin 11 comprises a flat semi-circular body of the desired width and describing an arc of greater radius than the pipes A lo being welded. Formed of fiber~lass, urethane or similar insulation material the semi-circular jaw covers a copper tube 14 that winds circuitously through the jaw with its spaced ends 15 and 16 formed with couplings for connection with the cables 8 from the control `~ panel 7- that similarly are hollow copper tubes and additional to supplying the induction current from the generator 6 carry a stream of water or antifreeze coolant circulated by a pump from a sump storage tank in a closed system. It is to be understood that the induction current or field by which the pipe is heated eminates from the copper tubing 14 enclosed in the jaw. The inductor must be held in spaced relation to the pipe to prevent sparking between them which could mar the pipe and ruin the in-ductor. Nevertheless, the efficiency of this air coupling in-duction is increased by lowering the frequency of the induction current as the wall thickness of the pipe increases and the closer the inductor is to the pipe the greater the efficiency of induction heating. Accordingly, in Figure 6 a plurality of ~-~
circumferentially spaced stops 17 will be seen on the inner side of the jaws 12-13 that engage the pipe 3 shown in dotted ` outline. ~-To balance the load for efficient operation and to enable an operator to vary the power input to the pipe ~ -and the duration of the heating period the control cabinet 7 includes such equipment as condensors and circuit items.
`` ` ~(~66783 The split-ring inductor jaws 12 and 13 that pivot on pin ll between the support arms 10 may each be actuated by a double acting hydraulic cylinder 20 pivoted at its closed end in a frame-mounted clevis - 21 and with the free end of its slidable rod 22 similarly pivoted in a clevis 23 on the outer circumference of the respective jaw approximately midway of its ends. A pair of hydraulic hoses 24 to and from a control valve and hydraulic punp connect with each cylinder 20 near opposite ends.
The low ambient temperatures mentioned herein refer to those encountered in extreme latitudes that may range from +32F to -70F
and possibly lower that can cause complex problems when welding.
~ Various changes may be made to the forms of invention : herein shown and described without departing from the spirit of the inven-tion or the scope of the following claims.
:` .
. ~, .
' ~
`,` ~
" ~
,: .
.. . .
.~, .. . .
' ~r :
- .
To obtain maximum results in welding under such conditions of low ambient temperature the circumference of the pipe for a distance of approximately four inches on each side of the weld joint should be preheated approximately one minute at a temperature within the range of approximately 250F to approximate-ly 650F.
To prevent the large mass of cold pipe fromquenching the weld as it is being made and to retard the cooling rate în the weld zone it is desirable and in some cases necessary to apply further heat. Following the welding the entire circumfer- -ential field can be normalized by induction heating to approximately ; 1550F and then cooling in air to produce a weld of finer grain size and avoid internal stresses.
In the present method the inductor is powered : by an induction generator in the range of a low frequency of approximately 60 cycles per second to a high frequency of approx-imately 450,000 cycles per second.
- In other aspects of ~ipe heating in low ambient temperatures the width of the circumferential band of the pipe, the temperature at which it should be heated and the duration of the heating period are varied.
Por example prior to bending the pipe it should be pr~eated for a length of approximately four feet for a period of ` four minutes and at a temperature of approximately 650F or within tho range of 500~ to 900F. While for painting and coating the weld ~oint the pipe should be heated for a length of approximately eight inches, the same as the weld p~eheat, for a period of approx-imately four minutes at a temperature of approximately 250F.
3_ 10~i6783 THE SPLIT-RING INDUCTOR:
.
It is common practice in mills manufacturing steel pipe to use a standard inductor for normalizing pipe, the long weld seam being normalized by a bar inductor while the body of the pipe is heated by a ring inductor. For preheating pipe being welded into a pipeline under low ambient temperature and for operating in the field alongside a pipeline route, a pancake split-ring inductor is employed that allows it to be applied laterally to and removed from the pipe and in addition the split-ring nature of the inductor breaks up eddy currents that form when a ring inductor is used~ such currents causing welding difficulties by affecting the weld disposition quality and pro-duction speed.
In the drawings, Figure 1 shows a welded pipe-line 1 with the unfinished end resting on a support skid 2 and a length of pipe 3 about to be welded into the pipeline is placed in end to end relation adjacent to and in alignment therewith, such pipe 3 being carried by a side boom tractor or crane. A
heater in the form of a split-ring pancake inductor 4 loosely en-circles the joint to be welded, overlying approximately four inches of each of the confronting pipes.
A portable unit is seen in the line diagram of Figure 2 designed to be supported on a suitable carrier that is -- moveable alongside a pipeline being constructed. Such a unit would include a diesel motor or other prime mover 5 driving an alternator generator 6 supplying power to control cabinet 7 and via flexible cables 8 to the inductor 4.
The split-ring inductor 4, Figures 3-7 inclusive, serviced from the control cabinet 7 by cables 8 may be mounted ;~ .
~30 on the same or a separate carrier such as a tractor or the like by means of its support structure 9 here shown as a vertical - -channel iron frame. Prom opposite sides of the frame a,longitud--4^
~ , , , . .. : , ~ . , ~ 0 6 67 8 3 inally spaced pair of parallel arms 10 project horizontally to carry the hinge pin 11 on which a pair of complementary semi-circular split-ring inductor jaws 12 and 13 pivot. The inductor 4 includes these two hingedly connected semi-circular jaws 12 and 13 to allow the inductor to be opened, applied laterally to a pipe and then closed to circumferentially embrace the pipe.
Each inductor jaw 12 and 13 hingedly mounted on the pin 11 comprises a flat semi-circular body of the desired width and describing an arc of greater radius than the pipes A lo being welded. Formed of fiber~lass, urethane or similar insulation material the semi-circular jaw covers a copper tube 14 that winds circuitously through the jaw with its spaced ends 15 and 16 formed with couplings for connection with the cables 8 from the control `~ panel 7- that similarly are hollow copper tubes and additional to supplying the induction current from the generator 6 carry a stream of water or antifreeze coolant circulated by a pump from a sump storage tank in a closed system. It is to be understood that the induction current or field by which the pipe is heated eminates from the copper tubing 14 enclosed in the jaw. The inductor must be held in spaced relation to the pipe to prevent sparking between them which could mar the pipe and ruin the in-ductor. Nevertheless, the efficiency of this air coupling in-duction is increased by lowering the frequency of the induction current as the wall thickness of the pipe increases and the closer the inductor is to the pipe the greater the efficiency of induction heating. Accordingly, in Figure 6 a plurality of ~-~
circumferentially spaced stops 17 will be seen on the inner side of the jaws 12-13 that engage the pipe 3 shown in dotted ` outline. ~-To balance the load for efficient operation and to enable an operator to vary the power input to the pipe ~ -and the duration of the heating period the control cabinet 7 includes such equipment as condensors and circuit items.
`` ` ~(~66783 The split-ring inductor jaws 12 and 13 that pivot on pin ll between the support arms 10 may each be actuated by a double acting hydraulic cylinder 20 pivoted at its closed end in a frame-mounted clevis - 21 and with the free end of its slidable rod 22 similarly pivoted in a clevis 23 on the outer circumference of the respective jaw approximately midway of its ends. A pair of hydraulic hoses 24 to and from a control valve and hydraulic punp connect with each cylinder 20 near opposite ends.
The low ambient temperatures mentioned herein refer to those encountered in extreme latitudes that may range from +32F to -70F
and possibly lower that can cause complex problems when welding.
~ Various changes may be made to the forms of invention : herein shown and described without departing from the spirit of the inven-tion or the scope of the following claims.
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. ~, .
' ~
`,` ~
" ~
,: .
.. . .
.~, .. . .
' ~r :
- .
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of heating pipe by induction when welding a length of pipe into a pipeline at the low ambient temperature en-countered in extreme latitudes that may range from +32°F to -70°F
and possibly lower comprising the steps of (a) preheating the pipe in the area where a weld joint is to be made, (b) heating while the weld is being made, and at least one of the following steps, (c) fur-ther heating during the quenching and (d) heating for normalizing.
and possibly lower comprising the steps of (a) preheating the pipe in the area where a weld joint is to be made, (b) heating while the weld is being made, and at least one of the following steps, (c) fur-ther heating during the quenching and (d) heating for normalizing.
2. The method of claim 1 wherein a length of pipe is placed adjacent to and aligned with the end of the last connected pipe of an unfinished pipeline, opening a portable split-ring induction heater, applying said heater laterally to the pipes in the area of their confronting aligned ends and closing said heater to circum-ferentially embrace the pipe area to be welded.
3. The method of claim 1, wherein the preheating is for a distance of approximately four inches on each side of the weld joint to be made during a period of approximately one minute at a tempera-ture within the range of approximately 250°F to approximately 650°F.
4. The method according to claim 1, wherein the normalizing can embrace the entire circumferential field and the induction heat-ing rises to approximately 1550°F.
5. A split-ring pancake induction heater for use when weld-ing pipe into a pipeline in low ambient temperature comprising a pair of separable jaws openable beyond the diameter of the pipe being welded for lateral application to extend over the pipe joint area and closeable to circumferentially embrace the same, wherein each of said jaws constitutes a separate inductor that tend to break up eddy currents causing welding difficulties by affecting the weld disposi-tion quality.
6. A split-ring induction heater according to claim 5 wherein said pair of jaws are hingedly connected and each has a flat semi-circular body enclosing an electrical conductor from which the induction current eminates.
7. An induction heater according to claim 6 wherein the semi-circular jaws are of insulating material and the enclosed conductors are hollow tubes supplied with a forced flow of coolant.
8. A split-ring induction heater according to claim 5 being part of a portable self-contained unit moveable alongside a pipe-line being constructed comprising a prime mover, an alternator generator driven thereby and supplying power through a control unit to said inductor heater.
9. An induction heater according to claim 8 wherein the unit includes a heater-supporting frame on which said pair of jaws is hingedly connected and each of said jaws is provided with a double acting hydraulic cylinder pivoted at opposite ends to the frame and jaw respectively.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,851A CA1066783A (en) | 1975-12-31 | 1975-12-31 | Method and apparatus for pipeline induction heating |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,851A CA1066783A (en) | 1975-12-31 | 1975-12-31 | Method and apparatus for pipeline induction heating |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066783A true CA1066783A (en) | 1979-11-20 |
Family
ID=4104880
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA242,851A Expired CA1066783A (en) | 1975-12-31 | 1975-12-31 | Method and apparatus for pipeline induction heating |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1066783A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2517164A1 (en) * | 1981-11-24 | 1983-05-27 | Cem Comp Electro Mec | METHOD AND DEVICE FOR OBTAINING A TRANSVERSAL HOMOGENEITY OF ELECTROMAGNETICALLY INDUCED HEATING OF LONG AND LONG PRODUCTS IN CONTINUOUS SCROLL |
| CN110681966A (en) * | 2019-10-18 | 2020-01-14 | 中国电建集团山东电力建设第一工程有限公司 | Pipeline welding heating device, welding device and method |
| CN114393413A (en) * | 2022-03-10 | 2022-04-26 | 中国铁塔股份有限公司黑龙江省分公司 | Installation, assembly and disassembly shackle machining device for truss iron tower |
-
1975
- 1975-12-31 CA CA242,851A patent/CA1066783A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2517164A1 (en) * | 1981-11-24 | 1983-05-27 | Cem Comp Electro Mec | METHOD AND DEVICE FOR OBTAINING A TRANSVERSAL HOMOGENEITY OF ELECTROMAGNETICALLY INDUCED HEATING OF LONG AND LONG PRODUCTS IN CONTINUOUS SCROLL |
| EP0080921A1 (en) * | 1981-11-24 | 1983-06-08 | Alsthom | Method and arrangement for realizing a transversal heating homogeneity by electromagnetic induction of long, thin, continuously advancing products |
| CN110681966A (en) * | 2019-10-18 | 2020-01-14 | 中国电建集团山东电力建设第一工程有限公司 | Pipeline welding heating device, welding device and method |
| CN114393413A (en) * | 2022-03-10 | 2022-04-26 | 中国铁塔股份有限公司黑龙江省分公司 | Installation, assembly and disassembly shackle machining device for truss iron tower |
| CN114393413B (en) * | 2022-03-10 | 2022-07-15 | 中国铁塔股份有限公司黑龙江省分公司 | Installation, assembly and disassembly shackle machining device for truss iron tower |
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