RU2657676C1 - Method for dehydrogenisation of welds of the main gas pipelines of large thickness - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention can be used to heat welded joints of main gas pipelines by radiation methods. In the manufacture of a welded seam, its temperature is measured and when reaching a temperature of 200–240 °C at one of the seam points above it is set the outlet device of the electron accelerator. Seam is irradiated by electrons, controlling the temperature of the welded seam. With a decrease in its temperature to 60–80 °C, an induction heater of a belt type is placed on the adjacent seam area and heated by it with a seam to a temperature of 220–240 °C. Then the heater is moved, an accelerator is placed in its place and the seam is irradiated by electrons. Repeat the process of heating and measuring the temperature and irradiation of the weld by electrons.

EFFECT: method provides for the complete removal of hydrogen from the welded seams of the main gas pipelines of large thickness during their manufacture.

1 cl, 3 dwg, 3 tbl

Description

The invention relates to the removal of hydrogen from materials by radiation methods and can be used to dissipate welds of main gas pipelines.

There is a method of de-scattering the walls of gas pipelines [RU 2402755 C2, IPC G01N 23/00 (2006.01), publ. 10.27.2010], for the implementation of which the irradiating device is moved along the entire length of the pipeline under the action of the transported gas, it is continuously irradiated with ionizing radiation of the pipe wall at a radiation dose rate of more than 0.015-0.018 R / s, a shock wave is generated by radiation, the hydrogen atmosphere in the walls is excited by the shock wave pipes stimulate the release of hydrogen from the walls of the pipe into the external atmosphere.

The disadvantage of this method is the use of an environmentally hazardous source of ionizing radiation, which cannot be turned off, which puts forward additional requirements for its storage and operation.

There is a method of dissoncing welds of gas pipelines [RU 2580582 C2, IPC (2006.01) V23K 37/00, V23K 31/02, V23K 28/00, publ. 04/10/2016], selected as a prototype, including the processing of welded joints of the pipeline by ionizing radiation to exit hydrogen from the pipe joint. During the execution of the weld, its temperature is continuously measured and, when a temperature of 200-240 ° C is reached at one of the weld points, an electron accelerator outlet device is installed above it and the weld is irradiated with electrons, the weld temperature is simultaneously controlled, and when the weld temperature is reduced to 60-80 ° C move the electron accelerator along the weld to its other points, with the repetition of the process of measuring temperature and irradiation of the weld.

Exposure to accelerator radiation due to the small range of electrons in steel does not allow hydrogen to be effectively removed over the entire thickness of the weld of the main gas pipe, since the weld has time to cool and high currents and higher electron beam energies are required. That is, the time of irradiation of pipes with walls of large thickness increases. This leads to cooling of the weld after welding. Therefore, it is necessary to use heating by an electron beam, which increases the time of suturing the seam and reduces the efficiency of the method. With increasing wall thickness, the time of electron irradiation increases, the temperature of the weld after welding decreases. This leads to a decrease in the rate of hydrogen removal and its incomplete removal.

The technical problem to which the invention is directed is the creation of a method for dissolving welds of thick-walled pipes of main gas pipelines, which allows for the removal of hydrogen and the elimination of embrittlement of welds of a gas pipeline with pipes of large thickness.

The method of dissolving welds of thick-walled pipes of main gas pipelines, as in the prototype, involves measuring the temperature of the resulting weld in the process of cooling and when an electron accelerator outlet device is installed above one of its temperature points 220-240 ° C, while irradiation of the weld with electrons with control of its temperature, when it decreases to 60-80 ° C, the electron accelerator is moved along the weld to the next point, after which the measurement process is repeated eratury and weld irradiation over its entire length, wherein the hydrogen content in the weld metal is determined depending on the value of the thermopower from the calibration graph.

According to the invention, in the process of irradiating the weld with electrons at the first point, the subsequent adjacent region of the weld is heated with a tape-type induction heater to 220-240 ° C, and when repeating the process of measuring temperature and irradiation at subsequent points of the weld, the heater is sequentially moved, repeating the process of heating the adjacent seam area.

The indicated temperature range is due to: at the lower boundary - the temperature below which radiation stimulation has practically no effect on the hydrogen output from the weld; along the upper boundary, the temperature above which the phenomenon of capture of excess hydrogen from the external atmosphere due to the dissociation of water and hydrocarbon impurities is possible.

It is known that when the temperature of the steel is 150-200 ° C, the time for the release of hydrogen from the steel is reduced and the degree of metal scattering is increased, since diffusion at 150-200 ° C is faster than at room temperature 20-30 ° C. However, simple heating and cooling do not lead to a complete dissolution of the pipeline seam, therefore, radiation-stimulated exposure is used. But when irradiated with an electron beam, a problem arises related to the small range of electrons in steel. Different thicknesses of pipe welds significantly affect the position of the maximum curve of the hydrogen exit from the weld. This is because the hydrogen flux J is equal to

,

,

where d is the wall thickness of the welded pipe (sample);

D (t) is the diffusion coefficient of hydrogen in the weld metal;

S is the area of the irradiated surface;

With ₀ - the initial concentration of hydrogen in the weld;

t is the time of exposure to the seam by electrons.

That is, the value of the outgoing hydrogen flow in a complex way depends on the thickness of the sample d. In addition, the diffusion coefficient D (t) depends on the temperature of the seam. Therefore, the control of the seam temperature becomes a determining factor. In the process of welding, the seam cools quickly and the time of the accelerator is not consistent with the temperature of the seam, in the place where the accelerator is installed. The dimensionless invariant of the rate of change in the hydrogen concentration in plane-parallel geometry is the quantity D (T) / H ² , which allows one to estimate the time t ₁ and t ₂ of hydrogen output for samples of different thicknesses H at different temperatures T (in experiments, the temperature in degrees Celsius is usually used (t ° С), and in theoretical calculations the temperature in degrees on the Kelvin scale (T K) is used):

t ₂ = t ₁ (H ₂ / H ₁ ) ² [D (T ₁ ) / D (T ₂ )].

The invariant can be obtained from the formula

C (x, t) = (4 / π) C ₀ exp (-π ² Dt / H ² ) sin (πx / H),

where H is the thickness of the sample,

D is the diffusion coefficient,

t is the time of suturing the seam when exposed to the seam by electrons,

x is the length of the seam.

Under conditions of radiation-stimulated gas evolution (GWHG), the maximum gas evolution flow occurs at a lower temperature and lower activation energy E _d (table 1).

The time to reach substantial purification steel sample hydrogen (hydrogen content of the steel about 5 cm ^3/100 g) due to thermally (TSGV) and hydrogen gas release stimulated radiation for sample 0.5 mm thick and 50 to 150 seconds, respectively.

From tables 1, 2 and 3 it can be seen that the time to achieve significant purification of the sample from hydrogen depends on the temperature of the weld and, in addition, on the wall thickness of the pipes being welded. When processing a seam with electrons in one of its places, the seam after welding has time to cool. In addition, when thermal heating to temperatures above 300 ° C (to reduce the time of exposure to an electron beam), it is difficult to dilute the seam, since in this case excess hydrogen is captured from the external atmosphere.

It is known that irradiation of hydrogenated pipeline steel leads to a significant improvement in the surface condition as a result of intense diffusion and the release of hydrogen from the metal [X. Baumbakh, M. Kroening, Yu.I. Tyurin et al. Metal-hydrogen nonequilibrium systems. Titanium, stainless steel. Tomsk: Publishing House Tom. University, 2002. S. 152]. Thermal heating with simultaneous exposure to electron beams is accompanied by a shift in the position of the maximum of the outgoing hydrogen stream from the steel to the low-temperature region. However, the value of this temperature substantially depends on the heating rate and the thickness of the material.

The test results showed (Fig. 1) that for samples of 12Kh18N10T steel, starting from a temperature value of t = 70 ° C (T = 343 K) up to a temperature of more than 200 ° C, the hydrogen concentration decreases by a factor of two, less as a result of scattering with simultaneous induction heating and irradiation than when irradiated without pre-heating. In addition, the minimum content of residual hydrogen in the weld, with simultaneous induction heating and irradiation, is already observed at a temperature of more than 140 ° C with simultaneous induction heating and irradiation. Further small changes in the concentration of hydrogen, near the achieved minimum value, can be considered background.

Thus, the proposed solution makes it possible to use the advantages of thermal heating to a certain temperature with the simultaneous exposure to electron beams, which causes intense diffusion and release of hydrogen from the metal, in the manufacture of a weld of thickened pipes of main gas pipelines. Thermal heating with simultaneous exposure to electron beams is accompanied by a shift in the position of the maximum of the outgoing hydrogen stream from the steel to the low-temperature region.

Table 1 presents the temperature T _max corresponding to the maximum hydrogen flux and the activation energy E _d at various heating rates β for the conditions of thermostimulated gas evolution (TSHV) and radiation-stimulated gas evolution (RSHW) for steel grade 12X18H.

Table 2 presents the dependence of the time of suture disintegration during thermal heating (TSHV) on temperature T for pipes with a thickness of 10 mm.

Table 3 shows the dependence of the seam dissolution time under radiation-thermal exposure (RSVG) and thermal heating (TSGV) on temperature T.

In FIG. Figure 1 shows the dependences of the hydrogen content in steel 12Kh18N10T (weld) on the temperature of the weld when it is irradiated with an electron beam (current 100 μA, beam energy 35 keV), where dependence 1 was obtained by irradiating the weld without preliminary heating; and dependence 2 - with simultaneous induction heating and irradiation.

In FIG. Figure 2 shows the weld diaphragm, where 1 is the weld of the pipe walls, 2 is a thermocouple, 3 is a temperature meter, 4 is an electron accelerator with an exhaust device, 5 is an induction heater, 6 is a movable holder for an electron accelerator.

In FIG. Figure 3 shows a calibration graph used to determine the hydrogen concentration by the thermo-emf method when welding a weld is not dehydrated; where 1 is the region of low hydrogen concentrations, 2 is the region of high hydrogen concentrations.

For welding of two steel sheets used 12X18H10T UONI electrodes 13/45 with the diameter of the rod 4 mm, which give variation in the hydrogen content in the weld metal: from 5.25 to 5.74 cm ^3/100 g was produced Surfacing electrode UONI 13/55, with a rod diameter of 4 mm, a current of Isv = 150 A, a voltage of Usv = 24 V. The electrode was calcined in accordance with the mode indicated on the package. Using a thermocouple 2 gauge temperature 3 in the welding process measured the temperature of the weld 1 at the junction of the welded sheets. After welding was completed, thermocouple 2 of temperature meter 3 Testo 905-T2 was placed on seam 1, the temperature of the seam was measured with thermocouple 2 of temperature meter 3 and, when the weld temperature reached 220 ° C, thermocouple 2 was moved along the seam to the next point, and to the place where it was thermocouple 2, placed the outlet device of the electron accelerator 4 brand 6ELV-mini. The energy of the electron beam was 35 keV, and the beam current was 100 μA. Weld 1 was irradiated with an electron beam of accelerator 4 until the temperature of the weld decreased to 60 ° C. Katran VKKIG-K induction heater belt 5 was placed on the adjacent weld area, the weld was heated to 220 ° С, heater belt 5 was displaced, accelerator 4 was placed in its place, and heater 5 was moved to a new weld point. The process was repeated along the entire length of the weld of the pipes being welded.

During the tests, the hydrogen content in the weld of the gas pipeline was recorded by the thermo-emf method according to the calibration graph of the dependence of the hydrogen content in the weld metal on the value of the thermo-emf (Fig. 3). The dependence of the thermoelectric power on the hydrogen content in steel contains a region of low hydrogen concentrations (1) and a region of high hydrogen concentrations (2). The process was repeated until the seam was completely diluted. Such a state of the weld metal was considered reached at values of thermoelectric power of 0.4 mV, which corresponds to (the content of hydrogen in steel - 5 cm ^3/100 g).

Using the proposed method allows to dilute the seams of thickened pipes of the main gas pipelines in the process of their manufacture, which, in turn, provides the opportunity to eliminate embrittlement of the seams of the gas pipeline and increases its service life.

Claims (1)

The method of dissolving welds of thick-walled pipes of main gas pipelines, including measuring the temperature of the resulting weld in the process of cooling and installing an electron accelerator outlet device above it when the temperature of 220-240 ° C is reached at one of its points, and the weld is irradiated with electrons with control its temperature, when it decreases to 60-80 ° С, the electron accelerator is moved along the weld to the next point, after which the process of measuring temperature and irradiation is repeated the weld along its entire length, and the hydrogen content in the weld metal is determined depending on the magnitude of the thermopower according to the calibration schedule, characterized in that during the irradiation of the weld with electrons at the first point, the next adjacent weld region is heated with a tape-type induction heater to 220-240 ° C, and when repeating the process of measuring temperature and irradiation at subsequent points of the weld, the heater is successively moved to repeat the process of heating the adjacent weld area.

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