CN117733472A - Welding repair method for WC9 casting and P91 pipeline of gas unit check valve - Google Patents

Abstract

A welding repair method for a WC9 casting of a gas unit check valve and a P91 pipeline comprises the following steps: (1) analyzing and judging crack properties; (2) According to the crack properties, determining a welding method and welding technological parameters: priming by using a TIG40 welding wire, filling and covering by using an R407 welding wire, controlling the temperature between preheating layers within 300 ℃, controlling the diameter of the TIG40 welding wire to be phi 2.5 and the diameter of the R407 welding wire to be phi 3.2, and simultaneously adopting small-current multilayer multi-channel rapid welding, wherein the welding speed is controlled to be 200-250 millimeters per minute; (3) Identifying a creep degradation area according to crack cracking properties and cleaning the creep degradation area by adopting a circular cutting mode; (4) And performing welding repair according to the established welding method and welding process parameters. The method can radically and thoroughly repair the cracking defect of the WC9 casting and the P91 welding joint, and can fully prolong the service life of the WC9 casting.

Description

Welding repair method for WC9 casting and P91 pipeline of gas unit check valve

Technical Field

The application relates to a welding repair method for pressure-containing members of a gas turbine unit, in particular to a welding repair method for WC9 castings and P91 pipelines in front of a check door of the gas turbine unit, and belongs to the technical field of gas power generation.

Background

As is well known, gas power generation refers to the generation of electricity from natural gas. On one hand, the gas power generation has the advantages of high efficiency and flexibility compared with the traditional power generation modes such as coal power and the like, can be started and stopped rapidly, and is suitable for the change of power requirements. On the other hand, the gas power generation can be combined with other renewable energy power generation modes to form a hybrid power generation system, so that the energy utilization efficiency is improved, and the emission of greenhouse gases is reduced. Therefore, the gas power generation is widely applied in the global scope, and becomes an important power generation mode.

At present, after a bearing member, such as a check door, of a gas turbine unit for gas power generation runs for a certain time, a phenomenon of dripping water of a pyrolling steam easily occurs, and the phenomenon of circumferential cracking of an original welded junction (namely a weld joint between WC9 and P91) of a manufacturer in front of the check door is found.

Aiming at the cracking problem of the WC9 casting and the P91 welding joint, the related repairing method in the prior art adopts a local repair method to carry out welding repair. The meaning of such local repair, i.e. where the crack is to be excavated, does not take into account that the uncracked site may have creep voids already created, and that cracks that will be formed cannot be foreseen and handled. Along with the extension of the running time, the holes are necessarily connected together to form cracks, so that the repair is incomplete, and the longer service life cannot be ensured.

Meanwhile, in the operation of welding repair, the conventional method in the prior art is to directly adopt the same welding material as a manufacturer to carry out local repair, namely adopt P91 welding material to carry out repair. In this way, creep cracks still occur too early after the WC9 side heat affected zone is operated for a period of time, and the technical problem cannot be fundamentally solved.

Disclosure of Invention

In order to overcome the defects of the related art, the application provides a welding repair method for a WC9 casting of a gas turbine unit check valve and a P91 pipeline, which can radically and thoroughly repair the cracking defect of a weld joint of the WC9 casting and the P91 pipeline and can fully prolong the service life of the weld joint.

The technical scheme adopted for solving the technical problems is as follows:

a welding repair method for a WC9 casting of a gas unit check valve and a P91 pipeline comprises the following steps:

(1) Analyzing and judging crack properties;

(2) Determining a welding method and welding process parameters corresponding to the following table according to the crack properties;

(3) Identifying a creep degradation area according to crack cracking properties and cleaning the creep degradation area by adopting a circular cutting mode;

(4) And performing welding repair according to the established welding method and welding process parameters.

As a further optional design of the application technical solution, the (1) analyzing and judging crack properties specifically includes:

(1.1) confirming the fracture site:

(1.1.1) cutting along two sides of the crack to obtain a sample;

(1.1.2) after the sample is cooled to room temperature, detecting the components of the sample by adopting a direct-reading spectrometer, and confirming that the cracking positions are WC9 base material components and P91 weld joint components respectively;

(1.2) confirming a cause of the cracking;

(1.2.1) wire-cutting the sample to prepare a sample containing cracks;

(1.2.2) carrying out microscopic analysis on the crack of the sample, and confirming that the specific position of the crack is a fine grain area of a heat affected zone on the WC9 side of the check valve, and creep voids appear near the crack; and judging the cracking property as IV-type creep crack of the heat affected zone.

As a further alternative design of the technical solution of the application, the (1.1.1) cutting along two sides of the crack to obtain a sample specifically includes:

the sample with triangular cross section was obtained by slicing with an angle grinder along both sides of the crack.

As a further optional design of the technical solution of the application, the process of cleaning the workpiece by adopting a circular cutting method further includes:

before circular cutting, fixing pipelines at two sides of a welded junction by using a cross frame, and welding the cross frame to a nearby rigid beam;

in the ring cutting, when the thickness is cut and 5mm remains, the ring cutting is stopped, and the cracks are removed by using a grinding wheel.

As a further optional design of the technical solution of the application, the welding method and the welding process parameters further include:

the temperature between preheating layers is controlled within 300 ℃ and the heat input is controlled below 10KJ/cm by adopting low-current multilayer multi-channel rapid welding.

As a further optional design of the technical scheme of the application, the step (4) of performing welding repair according to the formulated welding method and welding process parameters further includes:

carrying out constant temperature heat treatment at 740 ℃ for 1 hour after welding, controlling the temperature rising speed below 150 ℃, cooling to below 300 ℃ and air-cooling;

polishing and MT detection are carried out after the heat treatment is finished, and heat preservation is recovered after no defect is detected, and the repair is finished.

Compared with the related art, the welding repair method for the WC9 casting and the P91 pipeline of the gas turbine unit check valve provided by the application has the following technical advantages:

1) The application is based on the welding repair of WC9 and P91 welding line failure cause accurate analysis. For example, the welding is carried out by adopting P91 welding materials which are used by manufacturers in a conventional mode, the welding is carried out by adopting R407 low alloy steel in a targeted mode, the high-temperature creep property of the R407 welding line is equivalent to that of WC9, the high-temperature creep strength is lower than that of P91, and the R407 welding rod is selected for repairing, so that the creep degradation trend of a fine-grained region of a WC9 side heat affected zone can be slowed down.

2) The creep degradation areas are all cleared by adopting a whole circle circular cutting mode, so that the safety of subsequent service is ensured.

3) In the welding process, the welding repair of the method adopts all welding rods with the diameter of 3.2, the welding process strictly adopts small line energy multilayer multi-channel rapid welding, the line energy is controlled to be 10KJ/cm, the line energy is reduced by more than 50% compared with that of common manual welding (15-25 KJ/cm), a narrower heat affected zone can be obtained, the width of a WC9 side fine-grain zone can be greatly reduced, the IV type creep crack tendency is reduced, and the safe and stable operation of a unit can be ensured after repair.

4) By combining the points, after the WC9 and the P91 are welded and repaired by adopting the method, the service life of the joint is greatly prolonged, and the joint can be safely used for at least 3 years.

In addition to the technical problems, technical features constituting the technical solutions and beneficial effects brought by the technical features of the technical solutions described above, other technical problems that can be solved by the method for welding and repairing the check door WC9 cast piece and the P91 pipeline of the gas turbine unit, other technical features included in the technical solutions and beneficial effects brought by the technical features provided in the embodiments of the present application will be described in further detail in the detailed description of the present application

Drawings

The present application is further described below with reference to the drawings and examples.

FIGS. 1-2 are flow diagrams of a method for welding and repairing a WC9 casting of a gas turbine unit check valve and a P91 pipeline.

FIG. 3 is a graph of spectrometer search data obtained using the method of weld repair of the embodiments of the present application.

Fig. 4 is an image under an optical microscope obtained in a method of applying weld repair according to an embodiment of the present application.

Fig. 5 is an image under a scanning electron microscope obtained by applying the method of weld repair according to the embodiment of the present application.

Fig. 6 is a schematic diagram of a method of applying weld repair of an embodiment of the present application using derrick fixturing.

The meaning of the reference numerals in fig. 6, 1-wellbay; 2-weld.

FIG. 7 is a graph of heat treatment in a method of applying weld repair according to an embodiment of the present application.

Detailed Description

For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

1-2, the application provides a method for welding and repairing a WC9 casting of a check valve of a gas turbine unit with a P91 pipeline, which comprises the following steps:

(1) Analyzing and judging crack properties;

(2) Determining a welding method and welding process parameters corresponding to the following table according to the crack properties;

(3) Identifying a creep degradation area according to crack cracking properties and cleaning the creep degradation area by adopting a circular cutting mode;

(4) And performing welding repair according to the established welding method and welding process parameters.

Further, the (1) analyzing and judging the crack property specifically includes:

(1.1) confirming the fracture site:

(1.1.1) cutting along two sides of the crack to obtain a sample;

(1.1.2) after the sample is cooled to room temperature, detecting the components of the sample by adopting a direct-reading spectrometer, and confirming that the cracking positions are WC9 base material components and P91 weld joint components respectively;

(1.2) confirming a cause of the cracking;

(1.2.1) wire-cutting the sample to prepare a sample containing cracks;

(1.2.2) carrying out microscopic analysis on the crack of the sample, and confirming that the specific position of the crack is a fine grain area of a heat affected zone on the WC9 side of the check valve, and creep voids appear near the crack; and judging the cracking property as IV-type creep crack of the heat affected zone.

Further, the method (1.1.1) is characterized by cutting along both sides of the crack to obtain a sample, and specifically comprises the following steps:

the sample with triangular cross section was obtained by slicing with an angle grinder along both sides of the crack.

Further, the process of cleaning the material by adopting a circular cutting mode further comprises the following steps:

before circular cutting, fixing pipelines at two sides of a welded junction by using a cross frame, and welding the cross frame to a nearby rigid beam;

in the ring cutting, when the thickness is cut and 5mm remains, the ring cutting is stopped, and the cracks are removed by using a grinding wheel. In practice, the thickness can be measured in situ by a thickness gauge.

Further, the welding method and the welding process parameters further include:

the temperature between preheating layers is controlled within 300 ℃ and the heat input is controlled below 10KJ/cm by adopting low-current multilayer multi-channel rapid welding.

Further, the step (4) of performing welding repair according to the established welding method and welding process parameters further comprises the following steps:

carrying out constant temperature heat treatment at 740 ℃ for 1 hour after welding, controlling the temperature rising speed below 150 ℃, cooling to below 300 ℃ and air-cooling;

polishing and MT detection are carried out after the heat treatment is finished, and heat preservation is recovered after no defect is detected, and the repair is finished.

Example 1

In the related technology, the capacity of a domestic two-to-one unit of a certain combustion engine is 90 ten thousand kilowatts. And (3) during the temporary stop of the unit, the hot water drops before the check valve on the reheat pipeline at the position of 6.9 meters, then the heat preservation is removed for inspection, and the original welded junction of the manufacturer before the check valve is found to be cracked circumferentially, wherein the cracking position is 7 points to 9 points along the air flow direction, and the circumferential length is about 200mm, as shown in figure 1. Subsequent extensive inspection, it was found that there was also macroscopic circumferential cracking in the 3-to-6-point direction symmetrical to the location of the leak. Referring to the drawing of the medium-pressure check valve, the medium-pressure check valve is welded with a short pipe with the diameter of phi 711 multiplied by 16 multiplied by 100 (the outer diameter multiplied by the wall thickness multiplied by the length) before delivery, the short pipe is made of P91, the check valve body is made of WC9, and the welding seam is an original welding seam of a manufacturer. For such crack defects, limited construction periods, only weld repairs can be performed. The difficulty in field welding repair is that the temperature of the pipeline cannot be reduced to room temperature and is always kept at 200-250 ℃, and mainly because the pipeline at the other side of the cracking welded junction normally operates, the temperature is 566 ℃, and heat can be continuously transferred to the cracking welded junction.

In view of the above, the method for welding and repairing the WC9 casting of the check valve of the gas turbine unit and the P91 pipeline comprises the following specific steps.

Because the on-site pipeline temperature is higher, effective detection cannot be implemented, in order to confirm the cracking position, the embodiment of the application adopts the angle grinder slice to prepare the sample along the two sides of the crack, adopts the spectrometer to carry out component detection, and confirms the cracking position.

Referring to fig. 3, as can be seen from the detection result of the direct-reading spectrometer, the materials on both sides of the crack are respectively WC9 base material component and P91 weld component, and thus the fracture position is determined as the position near the weld joint line of the check valve body and the nipple joint close to the check valve body side.

In order to confirm the specific cause of cracking, the prepared sample is wire-cut to prepare a cross section sample at the tip of the crack and the position of breaking, the cross section sample is respectively inlaid, and after grinding, polishing and corrosion, the crack is subjected to tissue observation and microscopic analysis under an optical microscope and a scanning electron microscope in a metal laboratory.

Macroscopic structure morphology of the breaking position is visualized, and the breaking position is positioned in a fine grain area of a heat affected zone at the side of the check valve WC 9. At the same time, the vicinity of the crack was observed under an optical microscope at 500 times, and more holes were found to occur in the vicinity of the main crack, see fig. 4. Scanning electron microscope observation is carried out on the broken part of the sample, the broken position is found to be positioned at the joint heat affected zone part, and a large number of creep holes appear near the broken part, as shown in fig. 5.

Thus, the embodiment of the application judges that the cracking cause is a type IV creep crack in the heat affected zone of the check door WC 9.

According to the embodiment of the application, the following specific welding repair process is specially formulated through accurate analysis and judgment of crack properties.

In order to clean the creep degradation area as clean as possible, the defect is removed by adopting a whole circle circular cutting mode, and in order to prevent the pipeline from generating circumferential displacement in the cutting process, the pipelines at the two sides of the welded junction 2 are fixed by the cross frame 1 before cutting, and meanwhile, the cross frame is welded on a nearby rigid beam, as shown in fig. 6. Meanwhile, in order to prevent the pipeline from axial displacement in the circular cutting process, when the pipeline is cut to be 5mm, the circular cutting is stopped, and the cracks are removed by using a grinding wheel.

In order to reduce the line energy during welding, a narrower welding heat affected zone is obtained, and the IV type creep crack tendency is reduced; priming by adopting a TIG40 welding wire, and filling and capping by adopting an R407 welding rod; the temperature between the preheating layers is controlled within 300 ℃; the diameter of the TIG40 welding wire is phi 2.5, the diameter of the R407 welding rod is phi 3.2, and meanwhile, the small-current multilayer multi-channel rapid welding is adopted, and the welding speed is controlled to be 200-250 millimeters per minute; the heat input is controlled below 10KJ/cm (compared to the prior art, a person of ordinary skill would prefer to select a welding rod with a diameter of 4.0mm, with wire energy mostly in the range of 15-25KJ, with few demands to be controlled within 10 KJ); the specific welding process parameters are shown in table 1.

TABLE 1 welding process parameters

The specific welding needs to be noted: the ratio of the welded bead length of each complete welding rod to the melting length of the welding rod is greater than 50%, and the thickness of each layer of welding bead is not greater than the diameter of the welding rod. The swing amplitude of the welding rod is not more than 3 times of the diameter of the welding rod, and the joint parts are staggered. After each layer of welding seam is welded, sundries such as welding slag, splashing and the like are cleaned by a grinder or a steel wire brush (particularly attention should be paid to an intermediate joint and the edge of a groove), and after the self-checking is qualified, the next layer can be welded. The welding seam should be even, orderly and smooth, or the welding seam should be smooth by polishing with an angle grinder.

In order to sufficiently eliminate the welding residual stress, referring to fig. 7, a constant temperature of 740 ℃ is performed for 1 hour after welding; the temperature rise and drop speed is controlled below 150 ℃, and the temperature is cooled to below 300 ℃ for air cooling. Polishing after the heat treatment is finished, carrying out MT detection, recovering heat preservation after no defect, and finishing repair.

The gas unit check valve repaired by the method can safely and stably operate for at least 3 years, and defects are not found in magnetic powder detection and phased array detection of a welding joint during unit overhaul after 3 years. Metallographic examination was performed on the surface of the WC9 side heat affected zone, no creep voids were found, and no creep cracks were found. Proved by the welding repair method for the WC9 casting and the P91 pipeline of the gas turbine unit, the problem of field repair of original welded junction crack defects of a check valve manufacturer can be thoroughly and effectively solved.

The foregoing description is only a preferred embodiment of the present application, and is not intended to limit the present application in any way, and any simple modification and equivalent variation of the above embodiment according to the technical spirit of the present application falls within the scope of the present application.

Claims (6)

1. The method for welding and repairing the WC9 casting of the check valve of the gas unit and the P91 pipeline is characterized by comprising the following steps of:

(1) Analyzing and judging crack properties;

(2) Determining a welding method and welding process parameters corresponding to the following table according to the crack properties;

(3) Identifying a creep degradation area according to crack cracking properties and cleaning the creep degradation area by adopting a circular cutting mode;

(4) And performing welding repair according to the established welding method and welding process parameters.

2. The method for welding repair of a gas turbine unit check valve WC9 casting and a P91 pipe according to claim 1, wherein the (1) analyzing and judging crack properties specifically comprises:

(1.1) confirming the fracture site:

(1.1.1) cutting along two sides of the crack to obtain a sample;

(1.1.2) after the sample is cooled to room temperature, detecting the components of the sample by adopting a direct-reading spectrometer, and confirming that the cracking positions are WC9 base material components and P91 weld joint components respectively;

(1.2) confirming a cause of the cracking;

(1.2.1) wire-cutting the sample to prepare a sample containing cracks;

(1.2.2) carrying out microscopic analysis on the crack of the sample, and confirming that the specific position of the crack is a fine grain area of a heat affected zone on the WC9 side of the check valve, and creep voids appear near the crack; and judging the cracking property as IV-type creep crack of the heat affected zone.

3. The method for welding repair of a gas turbine unit check valve WC9 casting and a P91 pipe according to claim 2, wherein the (1.1.1) is a sample obtained by cutting along both sides of a crack, and specifically comprises:

the sample with triangular cross section was obtained by slicing with an angle grinder along both sides of the crack.

4. The method for welding repair of the check valve WC9 casting and the P91 pipeline of the gas turbine unit according to claim 1, wherein the process of cleaning the check valve WC9 casting by adopting a circular cutting mode comprises the following steps:

before circular cutting, fixing pipelines at two sides of a welded junction by using a cross frame, and welding the cross frame to a nearby rigid beam;

in the ring cutting, when the thickness is cut and 5mm remains, the ring cutting is stopped, and the cracks are removed by using a grinding wheel.

5. The method for welding repair of a gas turbine unit check valve WC9 casting and a P91 pipe according to any one of claims 1 to 4, wherein the welding method and welding process parameters further comprise:

the temperature between preheating layers is controlled within 300 ℃ and the heat input is controlled below 10KJ/cm by adopting low-current multilayer multi-channel rapid welding.

6. The method for welding repair of a gas turbine unit check valve WC9 cast piece and a P91 pipe according to claim 5, wherein (4) the welding repair is performed according to the established welding method and welding process parameters, and further comprising:

carrying out constant temperature heat treatment at 740 ℃ for 1 hour after welding, controlling the temperature rising speed below 150 ℃, cooling to below 300 ℃ and air-cooling;

polishing and MT detection are carried out after the heat treatment is finished, and heat preservation is recovered after no defect is detected, and the repair is finished.