CN108866314B - Method for ensuring heat treatment uniformity of large-diameter thick-wall pipe weld joint - Google Patents
Method for ensuring heat treatment uniformity of large-diameter thick-wall pipe weld joint Download PDFInfo
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 117
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- 229910000851 Alloy steel Inorganic materials 0.000 description 5
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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Abstract
The invention relates to a method for ensuring the heat treatment uniformity of a large-diameter thick-wall pipe weld joint, which comprises the following steps: the outer wall of the welding port position pipeline is heated, and meanwhile, the pipe cavity of the welding port position pipeline is heated, and then the inner wall of the pipeline is heated. The invention reduces the temperature difference between the inner wall and the outer wall of the welding seam of the large-diameter thick-wall pipeline by the heat treatment process of simultaneously heating the inner wall and the outer wall, achieves the purposes of eliminating the welding residual stress and improving the performance of a welding joint by the heat treatment, solves the problem of poor heat treatment of the inner wall of the pipeline, integrally realizes the purpose of uniform heat treatment of a weld crater, and particularly has more obvious heat treatment effect on the weld crater of the thick-wall pipeline.
Description
Technical Field
The invention relates to the technical field of welding heat treatment, and relates to a method for ensuring the heat treatment uniformity of a welding seam of a large-diameter thick-wall pipe.
Background
In industrial boilers, because of the relatively low operating pressures and temperatures, carbon steel is generally used, and low alloy steels are sometimes used. In a power station boiler, the working pressure and the temperature are high, and besides carbon steel and low alloy steel, some medium alloy steel and high alloy steel are also used. However, both industrial boilers and utility boilers have requirements on welding heat treatment of steel weldments in installation, maintenance and factory preparation, and thick-wall components such as main steam pipelines, reheating section pipelines and headers of ultra-supercritical boilers in power stations have the main problems of high weld hardness and low toughness in the installation process of the series of steel pipelines. In order to improve the properties of the welded joint and reduce the residual stress of the weld, the weld must be subjected to a post-weld heat treatment. Domestic and foreign researches show that the post-welding heat treatment temperature has great influence on the performance of the weld joint of the steel pipe, and the performance of the welded joint can be improved by carrying out tempering heat treatment on the weld joint for a certain temperature and time according to different steel types, so that the performance of the weld joint meets the standard and standard requirements. For example, the tempering temperature of the heat treatment recommended by the 9% Cr steel is 760 ℃ and 10 ℃, the heat treatment temperature can be used for obtaining the welding joint with good performances of the hardness of 185-270HB and the impact energy of 41J, when the heat treatment temperature is about 740 ℃, the constant temperature time needs to be prolonged to reach the same performance index, and when the temperature is below 730 ℃, the constant temperature time is prolonged, and the hardness value and the impact energy can hardly meet the standard specification requirements.
The post-welding heat treatment of the welded joint of the pipeline with large pipe diameter and large wall thickness in a piping manufacturing plant is generally carried out by adopting an electric heating furnace integral heat treatment method, the weld joint heat treatment is uniform, the batch heat treatment is convenient, but the economic cost is high, and the influence on the performance of the base metal of the pipeline is obvious.
The post-welding heat treatment of the pipeline welded joint with large pipe diameter and large wall thickness on site generally adopts crawler-type heating local heat treatment or medium-frequency induction heating local heat treatment. In the field heat treatment process, a heat source is generally only arranged on the outer wall of the pipeline, heat is conducted from the outer wall to the inner wall, and even if a steady state is achieved, a certain temperature difference necessarily exists between the inner wall and the outer wall. In order to ensure the performance of the whole welding joint, the temperature difference between the inner wall and the outer wall is necessary to be reduced as much as possible, but along with the increase of the working temperature and the working pressure of the boiler and the continuous increase of the wall thickness of the pipeline, the wall thickness of some parts is up to more than 150mm, and the temperature difference between the inner wall and the outer wall is increased correspondingly. Therefore, the control of the temperature difference between the inner wall and the outer wall becomes a problem to be solved urgently in the field installation of domestic pipelines at present. In response, much work has been done by researchers, focusing primarily on two parts: firstly, the distribution of a heat treatment temperature field is adjusted by controlling the heating width, the heat preservation width, the temperature rise and fall speed, the temperature control temperature and the ambient temperature, and the regularity is obvious and easy to implement; and secondly, reducing the temperature difference between the inner wall and the outer wall by controlling the air of the inner wall of the pipeline to penetrate through the hall and adjusting the heating device of the inner wall of the pipeline, wherein the inner wall heating device is a laminating pipeline inner wall for heating the inner wall, and has poor operability and poor practicability.
Disclosure of Invention
The invention aims to provide a method for ensuring the heat treatment uniformity of a large-diameter thick-wall pipe weld joint.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for ensuring the heat treatment uniformity of a large-diameter thick-wall pipe weld joint comprises the following steps: and heating the outer wall of the pipeline at the welding port position and simultaneously heating the pipe cavity of the pipeline at the welding port position.
Preferably, an internal heater is arranged inside the pipeline, and the internal heater heats the cavity of the pipeline through heat radiation and/or heat convection, so as to heat the inner wall of the pipeline.
When the inner wall of the pipeline is heated, the inner wall of the pipeline is heated in a heat radiation and heat convection mode by adopting a heating mode which is not attached to the inner wall of the pipeline.
Further preferably, the internal heater is arranged on the axis of the pipeline, and is preferably arranged symmetrically with the crater to be heat-treated as the center.
Further preferably, the internal heater is disposed on the axis of the pipe. The internal heater carries out heat radiation from the middle part of the pipe cavity of the pipeline to the inner wall of the pipeline, and reduces the temperature difference between the inner wall and the outer wall of the pipeline.
Further preferably, two ends of the pipe cavity of the pipeline at the position of the welded junction are respectively provided with a blocking plate, and the internal heater is positioned between the blocking plates at the two ends.
Further preferably, an auxiliary heater is provided in the blocking plate. The auxiliary heater can carry out auxiliary heating, and the air convection in the pipe cavity of the pipeline is increased by matching with the blocking plates at the two ends.
Preferably, an external heater is provided outside the duct, said external heater heating the outer wall of the duct by means of thermal radiation and/or conduction.
Further preferably, the external heater is coated on the outer wall of the pipe at the position of the weld opening, and an insulating layer is coated on the external heater.
Further preferably, the external heater is a track heater or an electromagnetic induction heater or a combination of the track heater and the electromagnetic induction heater.
Preferably, temperature measuring components are arranged inside and outside the pipeline, and the temperature field distribution of the outer wall and the pipe cavity of the pipeline is adjusted in real time according to the temperature measured by the temperature measuring components. The temperature measuring part can adopt a thermocouple, for example.
The local heat treatment of the crater belongs to the transient heat conduction process, and according to the invention, the whole transient heat analysis process of the heat treatment can be simplified as follows: temperature of heaterT=f(x，y，z，t)(ii) a Heat flow input from inner and outer surface of pipelineq=-k∂T/∂n(ii) a Convection heat transfer between inner and outer surfaces of pipeline∂T/∂n=-h(T w -T f )(ii) a Heat transfer from pipe cross section∂ /∂x(k∂T/∂x)+ ∂/∂y(k∂T/∂y)+ ∂/∂z(k∂T/∂z)+ q r =ρc∂T/∂t(ii) a Pipe radiation heat exchange∂T/∂n=-σ(T4 1-T4 2). Wherein,Tit is the temperature that is set for the purpose,qas the density of the heat flow,q r the intensity of the internal heat source is the intensity of the internal heat source,kin order to be a heat transfer coefficient,ρis the density of the material and is,cis the specific heat of the material, and the specific heat of the material,tas a matter of time, the time is,nin the direction of the normal to the boundary surface,hin order to obtain a convective heat transfer coefficient,in order to be the rate of radiation,σ=5.67×10 -8 W/m 2 ·K 4 is the stefan-boltzmann constant,T w is the temperature of the surface of the material,T f is the temperature of the tube cavity, and is,T 1 is the temperature of the heater, and is,T 2 is the material temperature.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages and effects:
the invention reduces the temperature difference between the inner wall and the outer wall of the welding seam of the large-diameter thick-wall pipeline by the heat treatment process of simultaneously heating the inner wall and the outer wall, achieves the purposes of eliminating the welding residual stress and improving the performance of a welding joint by the heat treatment, solves the problem of poor heat treatment of the inner wall of the pipeline, integrally realizes the purpose of uniform heat treatment of a weld crater, and particularly has more obvious heat treatment effect on the weld crater of the thick-wall pipeline.
Drawings
FIG. 1 is a schematic representation of a heat treatment process in the present application;
FIG. 2 is a schematic view of a heat treatment apparatus used in the present embodiment;
FIG. 3 is a schematic view of the heat treatment of the first embodiment;
FIG. 4 is a schematic cross-sectional view of the first embodiment;
FIG. 5 is a schematic view of the heat treatment of the second embodiment;
FIG. 6 is a schematic cross-sectional view of the second embodiment.
Wherein: 1. a pipeline; 10. welding a welding opening; 11. a lumen; 2. an internal heater; 3. a blocking plate; 4. an auxiliary heater; 5. an external heater; 6. a heat-insulating layer; 7. and a thermocouple.
Detailed Description
The invention is further described below with reference to the accompanying drawings and embodiments:
a method for ensuring the heat treatment uniformity of a welding seam of a large-diameter thick-wall pipe generally has the specification ranges of: an outer diameter generally greater than 325mm is referred to as a major diameter, and a thick wall generally greater than 20mm is referred to as a thick wall.
Comprises heating the outer wall of the pipeline 1 at the position of the welding opening 10 and simultaneously heating the pipe cavity 11 of the pipeline 1 at the position of the welding opening 10. The method specifically comprises the following steps:
an internal heater 2 is arranged inside the pipeline 1, the internal heater 2 heats the pipe cavity 11 of the pipeline 1 and heats the inner wall of the pipeline 1 in the forms of heat radiation and heat convection, in order to ensure the heating uniformity, the extending direction of the internal heater 2 is consistent with the axial lead direction of the pipeline 1, and preferably, the internal heater 2 is arranged on the axial lead of the pipeline 1 and symmetrically arranged by taking the welding opening 10 as the center.
Set up closure plate 3 respectively at the 11 both ends of lumen of weld opening 10 position pipeline 1, internal heater 2 is located between the closure plate 3 of both ends to set up auxiliary heater 4 in closure plate 3, internal heater 2 carries out the primary heating, and auxiliary heater 4 carries out the auxiliary heating, heats the inner wall of pipeline 1 with the mode of heat radiation and to the thermal current is direct and/or indirect.
An external heater 5 is arranged outside the pipe 1, and the external heater 5 heats the outer wall of the pipe 1 through heat radiation and/or heat conduction, in the embodiment: the external heater 5 is coated on the outer wall of the pipeline 1 at the position of the weld opening 10, and the external heater 5 is coated with the heat preservation layer 6. The external heater 5 adopts a crawler-type heater, an electromagnetic induction heater or a combination of the crawler-type heater and the electromagnetic induction heater.
Temperature measuring components are arranged inside and outside the pipeline 1, a thermocouple 7 is taken as an example, the thermocouples 7 are arranged on the internal heater 2, the auxiliary heater 4 and the external heater 5, and the output power of each heater can be adjusted at any time through real-time temperature control and measurement of the thermocouples 7 so as to integrally adjust the temperature field distribution of the craters 10 to be subjected to heat treatment.
In order to facilitate the arrangement of the internal heater 2, the heat treatment equipment shown in fig. 2 is specially designed, and comprises a connecting rod a, a heating control component b, a support frame component, a guide wheel d and a heat preservation component e. Wherein:
the internal heater 2, the support frame assembly and the guide wheel d are arranged on the connecting rod a, and the heat preservation component e is arranged on the support frame assembly. The connecting rod a is a rigid rod piece; the heating control component b is connected to one end of the connecting rod a through a flexible connecting pipe f, so that operation and control are facilitated; the heat preservation component e can adopt heat preservation cotton and the like.
The support frame assembly comprises a first support frame c1 and a second support frame c2, the first support frame c1 and the second support frame c2 are respectively located on two sides of the internal heater 2, when the first support frame c1 and the second support frame c2 are unfolded, the first support frame c1 and the second support frame c2 are abutted to the inner wall of the pipeline 1, the effect of the plugging plate 3 is achieved by combining the heat preservation part e, and the auxiliary heater 4 is arranged on the first support frame c1 and the second support frame c 2. The support frame adopts the principle similar to "umbrella", can realize freely expanding, folding according to the demand, controls the angle of expansion in order to cooperate the demand of different internal diameter pipes when expanding according to the pipeline internal diameter, plays the fixed action.
When in use: conveying the heat treatment equipment to the position of a weld crater 10 of the pipeline 1 through a guide wheel d, and ensuring that the built-in heater 2 is positioned in the center of a weld; unfolding the first support bracket c1 and the second support bracket c 2; the lumen 11 of the tube 1 is heated according to a heat treatment process.
The first embodiment is as follows:
the drum body of a certain pressure vessel steam drum is made of low alloy steel SA-299, the inner diameter is phi 1778mm, the upper wall thickness is 196.1mm, the lower wall thickness is 163.9mm, the total length of two end enclosures is 28.91m, two circumferential welds on the drum body have overproof defects such as cracks and inclusions, and part of the defects show penetrability of the inner wall and the outer wall, the process after welding repair is finished requires that two circumferential welds after repair welding are subjected to local postweld heat treatment, the constant temperature of the heat treatment is 550 ℃, and the temperature rising and falling speed does not exceed 50 ℃/h.
The method is adopted to carry out local postweld heat treatment on the two circumferential welds, and the specific implementation steps are as follows:
(1) selection of heating power
According to the requirements of postweld heat treatment process, a heating power calculation formulaP=KWC（T a -T b ）/3600t. Wherein,Pthe power required for heating;Kis the heat dissipation loss coefficient;Wweight of the heated part in the heating range;Cmaterial specific heat capacity;T a is the heating starting temperature;T b the final temperature for heating;theating time is used. Is calculated to obtainThe minimum power required by heating two circumferential welds of the cylinder body is 800kW, the main power of the external heater is 800kW in consideration of the power reserve, and the internal heater is 480kW as auxiliary heating selected power, so that the effect of accelerating the temperature equalization of the inner wall and the outer wall is achieved. Therefore, the project is applied to 4 heat treatment machines with 360KW power.
(2) Arrangement of heaters
As shown in fig. 3 and 4 (two welding seams are taken as an example in the present embodiment, and only one welding seam is shown in the figure): wherein, the circumferential weld crater 10a is subjected to heat treatment, and during the heat treatment, the requirement of temperature uniformity is considered, and a heat treatment scheme of internal and external combined heating is adopted. The external heaters are crawler- type heaters 50 and 51, about 80 pieces of heaters are 800kW, wherein the crawler-type heater 50 is a main heater, the crawler-type heater 51 is an auxiliary heater, a welding seam is taken as a center, the heating width is not less than 3 times of the thickness of the steam pocket wall along each side of the two sides of the center of the welding seam at the repairing position, and the heating width is set to be 600mm on one side; the internal heaters adopt frame heaters 20 (20 a, 20b and 20 c) which are 16 groups, 48 sheets and 480kW in total, the arrangement parts of the frame heaters 20 take a repaired circumferential weld as the center, the two sides of the repaired circumferential weld are respectively provided with 1000mm, two sides of the circumferential weld to be processed in the steam pocket are respectively provided with a blocking plate 3, an auxiliary heater 4 is arranged in the blocking plate 3, and thermocouples are simultaneously arranged inside and outside the circumferential direction of a workpiece according to standard specifications.
(3) Setting a postweld heat treatment process curve according to postweld heat treatment process parameters, wherein the maximum temperatures of an internal heater and an external heater are respectively 500 ℃ and 550 ℃, keeping the temperature for 10 hours, the heating and cooling rate is not more than 50 ℃/h, and the internal heater and the external heater are simultaneously heated for postweld heat treatment.
In engineering construction, a temperature measuring instrument is used for measuring the temperature of a heating area, a dial indicator is used for measuring the expansion amount of a steam drum, nondestructive inspection (including ultrasonic inspection, magnetic powder inspection, metallographic inspection, hardness inspection and residual stress inspection) is carried out after heat treatment, and various indexes are displayed to meet the technical requirements of heat treatment after welding.
Example two:
the drum body of a certain pressure vessel steam drum is made of low alloy steel SA-299, the outer diameter is 2200mm, the wall thickness is 195mm, the total length of end sockets on two sides is 27.2m, the drum body is composed of 8 sections of drum bodies and two end sockets, the overproof defect exists in the range of 1.49m in the longitudinal welding line between the 2 nd and the 3 rd circumferential welding lines, the distance between the defect position and the outer wall is 136-146 mm, the defect is eliminated from the inner wall, after welding repair, local postweld heat treatment is carried out on the longitudinal welding line, the constant temperature requirement of the heat treatment is 550 ℃, and the temperature rising and falling speed is not more than 50 ℃.
The method is adopted to carry out local postweld heat treatment on the two circumferential welds, and the specific implementation steps are as follows:
(1) selection of heating power
When the heating rate of the postweld heat treatment process is 50 ℃/h, the calculated main heat source power required by heating the longitudinal weld of the cylinder body is 680kW, the main power of the external heater is 680kW, and the internal heater is 240kW as auxiliary heating power, so that the effect of accelerating the temperature equalization of the inner wall and the outer wall is achieved. Therefore, the maximum heating power in the project is 920kW, and 4 heat treatment machines with 180kW power and 1 240kW power are used in total.
(2) Arrangement of heaters
As shown in fig. 5 and 6: wherein, the longitudinal weld seam crater 10b is subjected to heat treatment, and a heat treatment scheme of internal and external combined heating is adopted in consideration of the requirement of temperature uniformity during the heat treatment. The external heaters are crawler- type heaters 52 and 53 with about 68 pieces of heating power of 680kW, wherein the crawler-type heaters 52 are used as auxiliary heaters, the longitudinal welding line is used as a middle area, and the heating width is 2000mm along the longitudinal direction of the welding line at the repaired position; the internal heaters adopt frame heaters 22 (22 a, 22b and 22 c) which are 8 groups, 24 pieces and 240kW in total, the arrangement parts of the frame heaters 22 use the repaired longitudinal welding line as the center, 1600mm is arranged along the direction of the repaired longitudinal welding line, and a plurality of temperature control and temperature measurement thermocouples are simultaneously arranged on the upper, lower, left and right sides of the circumference of the steam drum and the inner and outer walls of the repaired welding line according to standard specifications.
(3) Setting a postweld heat treatment process curve according to postweld heat treatment process parameters, wherein the highest temperature of an internal heater and an external heater is 550 ℃, keeping the temperature for 6h, the temperature rising and falling rate is not more than 50 ℃/h, and the internal heater and the external heater are simultaneously heated for postweld heat treatment.
In engineering construction, a temperature measuring instrument is used for measuring the temperature of a heating area, a dial indicator is used for measuring the expansion amount of a steam drum, nondestructive inspection (including ultrasonic inspection, magnetic powder inspection, metallographic inspection, hardness inspection and residual stress inspection) is carried out after heat treatment, and various indexes are displayed to meet the technical requirements of heat treatment after welding.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (3)
1. A method for ensuring the heat treatment uniformity of a large-diameter thick-wall pipe weld joint is characterized by comprising the following steps: the method comprises the following steps: the outer wall of the pipeline at the welding port position is heated, simultaneously, the pipe cavity of the pipeline at the welding port position is heated, and then the inner wall of the pipeline is heated,
the method comprises the following steps that an internal heater is arranged inside a pipeline, the internal heater heats a pipe cavity of the pipeline in a heat radiation and/or heat convection mode, so that the inner wall of the pipeline is heated, the extending direction of the internal heater is consistent with the axial lead direction of the pipeline, and the internal heater is arranged on the axial lead of the pipeline and symmetrically arranged by taking a weld joint to be subjected to heat treatment as a center;
two ends of a pipe cavity of the pipeline at the position of the welded junction are respectively provided with a blocking plate, the internal heater is positioned between the blocking plates at the two ends, and an auxiliary heater is arranged in the blocking plate;
and an external heater is arranged outside the pipeline, the external heater heats the outer wall of the pipeline in a heat radiation and/or heat conduction mode, the external heater is coated on the outer wall of the pipeline at the position of the weld opening, and a heat insulation layer is coated on the external heater.
2. The method for ensuring the heat treatment uniformity of the weld joint of the large-diameter thick-wall pipe according to claim 1, wherein the method comprises the following steps: the external heater adopts a crawler-type heater or an electromagnetic induction heater or the combination of the crawler-type heater and the electromagnetic induction heater.
3. The method for ensuring the heat treatment uniformity of the weld joint of the large-diameter thick-wall pipe according to claim 1, wherein the method comprises the following steps: temperature measuring components are arranged inside and outside the pipeline, and the temperature field distribution of the outer wall and the pipe cavity of the pipeline is adjusted in real time according to the temperature measured by the temperature measuring components.
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| CN101264561A (en) * | 2008-05-05 | 2008-09-17 | 河北省电力研究院 | Pipeline welding inside heating method |
| CN107641702B (en) * | 2017-10-16 | 2019-10-11 | 山东电力建设第一工程公司 | A kind of post weld heat treatment method of major diameter thick-walled pipe |
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2018
- 2018-07-04 CN CN201810722902.4A patent/CN108866314B/en active Active
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