Welding method for martensite heat-resistant steel of reheating boiler

Abstract

The invention relates to the technical field of dissimilar steel welding, in particular to a martensitic heat-resistant steel welding method for a reheating boiler, which comprises the following steps: cleaning the surface of a welding area by using a proper solvent, removing greasy dirt and dirt on the surface, polishing the surface of the welding area by using a grinding wheel or a grinding disc, and removing rust and oxide. The modules of the boiler are placed on a movable temporary supporting object, measurement is conducted through a laser range finder, adjustment is conducted at the same time, it is guaranteed that the modules are aligned, the modules of the boiler are welded in a mode that every two modules of the boiler serve as a group, a plurality of welding assemblies are formed, measurement alignment is conducted through the laser range finder again, and the welding assemblies are welded. During welding, the welding temperature is monitored in real time through a temperature sensor, welding assemblies are welded mutually to form a reheating boiler, the positions near the ends to be welded are cleaned before welding, the situation that the welding quality is affected due to unstable welding arcs and uneven molten pools is prevented, and the welding quality is improved by removing rust and oxide. Welding defects such as poor welding seams, cracks and air holes are prevented.

Description

Technical Field

[0001] The invention relates to the technical field of welding of dissimilar steels, and in particular to a welding method of martensitic heat-resistant steel for a reheat boiler. Background Art

[0002] Since 2006, the Iron and Steel Research Institute has carried out exploratory research on the composition optimization and variety screening of 650℃ heat-resistant steel with 9%Cr~12%Cr~15%Cr content, relying on the international cooperation project "R&D and Performance Research of Boiler Steel Varieties of Ultra-supercritical Thermal Power Units with 650℃ Steam Parameters", and determined the direction and basic chemical composition system for the development of 650℃ martensitic heat-resistant steel with 9%Cr content; since 2009, relying on the 973 Program of the Ministry of Science and Technology of China "Basic Research on the Organization Stability of High-temperature Resistant Martensitic Steel", it has carried out basic research on the high-temperature organizational stability of 650℃ martensitic heat-resistant steel with 9%Cr content, proposed the "Selective Strengthening Design Theory" of 650℃ martensitic heat-resistant steel, and successfully developed the 10Cr9W3Co3VNbCuBN prototype steel.

[0003] Martensitic heat-resistant steel has a high alloy content and is difficult to weld. The post-blanching heat treatment process has strict requirements. If the welding and heat treatment process parameters are improperly selected, welding defects such as root oxidation, cold cracks, and hot cracks are likely to occur, resulting in unqualified weld quality and rework, thereby increasing construction costs, and affecting construction period and welding quality. Especially after the unit has been in operation for many years, the weld will have a major safety hazard. By selecting appropriate process parameters and controlling the entire process of welding personnel, welding materials, welding equipment and welding processes, each construction link is controlled and strictly implemented in accordance with the welding and heat treatment process parameters to ensure the welding quality of the weld and improve the service life of the weld. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art that after the welding of the reheat boiler, welding defects such as root oxidation, cold cracks, hot cracks, etc. of the weld seam cause rework due to unqualified welding quality, thereby increasing construction costs, affecting the construction period and welding quality, etc., and a reheat boiler martensitic heat-resistant steel welding method is proposed.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A welding method for martensitic heat-resistant steel for a reheat boiler is designed, comprising the following steps:

[0007] S1. Clean the end of the boiler module that needs to be welded, use an appropriate solvent to clean the surface of the welding area, and remove the oil and dirt on the surface;

[0008] S2. Use a grinding wheel or abrasive disc to grind the surface of the welding area to remove rust and oxides to ensure a smooth surface;

[0009] S3. Place the boiler module on a movable temporary support, measure it with a laser rangefinder, and make adjustments to ensure the module is aligned;

[0010] S4, welding the boiler modules in groups of two to form a plurality of welded assemblies, and measuring and aligning them again by means of a laser rangefinder. During welding, the welding temperature is monitored in real time by means of a temperature sensor, and the welding temperature is between 500°C and 1000°C;

[0011] S5. Weld the welding components together to form a reheat boiler, observe with the naked eye whether deformation occurs, and further measure with a measuring instrument;

[0012] S6. After the welding part of the reheat boiler has cooled down, measure it again with the measuring instrument to check whether deformation occurs.

[0013] Furthermore, in step S1, the solvent is an acetone solvent or an alcohol solvent, and is loaded into a spraying device and sprayed toward the welding area to clean the welding area multiple times.

[0014] Furthermore, in step S2, if there are scratches or depressions on the surface of the welding area, use a grinding tool to repair it to ensure that the surface of the welding area is flat, and use a clean rag or detergent to thoroughly wipe the surface of the welding area.

[0015] Furthermore, in step S3, the welding area of ​​the boiler module is preheated at a heating temperature of 200° C. to reduce deformation and residual stress during welding and ensure the performance of the welded joint.

[0016] Furthermore, in step S3, the placed boiler module is subjected to flaw detection by an ultrasonic flaw detector or a radiographic flaw detector, and a movable support is used as a temporary support to facilitate adjustment of the position of the boiler module.

[0017] Furthermore, in step S4, during welding, a clamp or a supporting structure may be used to align and fix the two modules, and a temporary support may be fixed at the same time to prevent the two modules from being misaligned during welding.

[0018] Furthermore, in step S4 and step S5, during welding, argon arc welding technology is first used for positioning welding. After positioning welding is completed, after confirming that there are no defects, welding is started along the module welding area close to the inner wall. The thickness of the weld is 1 / 3 of the wall thickness of the martensitic heat-resistant steel, and then filling welding is performed.

[0019] Furthermore, after welding is completed, the weld is inspected by an ultrasonic flaw detector or a radiographic flaw detector, and the weld with problems is cut, ground and re-welded.

[0020] Furthermore, in step S4, the welding current is 110-140A and the voltage is 18V.

[0021] Furthermore, before welding in step S4, a martensitic heat-resistant steel groove is prepared, the groove is a Y-shaped groove, the groove angle is 60 degrees to 90 degrees, the gap is 2 to 3 mm, and the blunt edge is 1 to 1.5 mm.

[0022] The invention provides a method for welding martensitic heat-resistant steel for a reheat boiler, which has the following beneficial effects:

[0023] In the present invention, by cleaning the vicinity of the end to be welded before welding, the welding arc is prevented from being unstable and the molten pool is uneven, thereby affecting the welding quality. By removing rust and oxides, welding defects such as poor welds, cracks, pores, etc. are prevented from occurring, thereby avoiding affecting the strength and stability of the welded joint.

[0024] Secondly, in the present invention, the welding area of ​​the boiler module is preheated to reduce deformation and residual stress during welding, ensure the performance of the welded joint, and weld the boiler modules in groups of two to form a plurality of welded assemblies, which are then welded together to ensure alignment and welding quality. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0026] A method for welding martensitic heat-resistant steel for a reheat boiler comprises the following steps:

[0027] S1. Clean the end of the boiler module that needs to be welded, use an appropriate solvent to clean the surface of the welding area, and remove the oil and dirt on the surface;

[0028] S2. Use a grinding wheel or abrasive disc to grind the surface of the welding area to remove rust and oxides to ensure a smooth surface;

[0029] S3. Place the boiler module on a movable temporary support, measure it with a laser rangefinder, and make adjustments to ensure the module is aligned;

[0030] S4, welding the boiler modules in groups of two to form a plurality of welded assemblies, and measuring and aligning them again by means of a laser rangefinder. During welding, the welding temperature is monitored in real time by means of a temperature sensor, and the welding temperature is between 500°C and 1000°C;

[0031] S5. Weld the welding components together to form a reheat boiler, observe with the naked eye whether deformation occurs, and further measure with a measuring instrument;

[0032] S6. After the welding part of the reheat boiler has cooled down, measure it again with the measuring instrument to check whether deformation occurs.

[0033] In the present invention, the vicinity of the end to be welded is cleaned before welding to prevent the welding arc from being unstable and the molten pool from being uneven, thereby affecting the welding quality. The surface of the welding area is polished by a grinding wheel or a grinding disc to remove rust and oxides, thereby preventing welding defects such as poor welds, cracks, pores, etc., and avoiding affecting the strength and stability of the welded joint.

[0034] Furthermore, in the present embodiment, in step S1, the solvent is an acetone solvent or an alcohol solvent, and is loaded into a spraying device and sprayed onto the welding area, and the welding area is cleaned multiple times. Acetone and alcohol are both volatile solvents, and evaporate quickly after use, and can quickly clean oil and dirt from the surface. After evaporation, no residue or water stains will be left, and the surface of the welding area can be kept clean to avoid affecting the welding quality.

[0035] In this embodiment, in step S2, if there are scratches or dents on the surface of the welding area, a grinding tool is used to repair it to ensure that the surface of the welding area is flat, and a clean rag or detergent is used to thoroughly wipe the surface of the welding area to eliminate potential weaknesses in the welding area, improve the connection strength of the welding joint, ensure the firmness and durability of the welding, and the flat surface helps to ensure the stable transmission of the welding arc, ensure the stability of the welding process and reduce the risk of welding deformation, thereby improving the welding quality.

[0036] Furthermore, in this embodiment, in step S3, the welding area of ​​the boiler module is preheated at a heating temperature of 200°C to reduce deformation and residual stress during welding and ensure the performance of the welded joint. By preheating, the temperature gradient of the welding area can be reduced, the residual stress caused by welding can be reduced, and the risk of weld cracks and deformation can be reduced. After welding, the weld can be wrapped with insulation material to slowly reduce the temperature of the weld so that the stress inside the weld can be released, thereby reducing the deformation and residual stress of the weld and improving the performance and quality of the welded part. Post-heat treatment can usually improve the mechanical properties, corrosion resistance, toughness and hardness of the welded joint, and active heating is required to maintain the temperature of the welded part when the ambient temperature is low.

[0037] In this embodiment, in step S3, the placed boiler module is subjected to flaw detection by an ultrasonic flaw detector or a radiographic flaw detector. A movable support is used as a temporary support to facilitate adjustment of the position of the boiler module. The flaw detection can help to find various defects in the welded joints, such as cracks, pores, inclusions, etc. These defects may affect the quality and strength of the welded joints. The flaw detection can timely detect and repair them. The quality of the welded joints can also be evaluated to ensure that no obvious defects occur during the welding process or that the defects are effectively repaired, thereby improving the quality and reliability of the welded joints.

[0038] It should be noted that in this embodiment, in step S4, a clamp or a supporting structure can be used to align and fix the two modules during welding, and a temporary support can be fixed at the same time to prevent the two modules from being misaligned during welding. A clamp for fixing large round pipes can be used to fix the pipes in the desired position to ensure stability and accuracy during the welding process. The support uses an adjustable height support, such as a lifting platform, to facilitate the alignment of the modules.

[0039] In this embodiment, in step S4 and step S5, during welding, argon arc welding is first used for positioning welding. After positioning welding is completed, after confirming that there are no defects, manual welding is used to weld along the portion of the module welding area close to the inner wall. The thickness of the weld is 1 / 3 of the wall thickness of the martensitic heat-resistant steel, and then filling welding is performed.

[0040] In addition, in this embodiment, after welding is completed, the weld is inspected by ultrasonic flaw detector or radiographic flaw detector, the problematic weld is cut and re-grinded for welding, and the weld is inspected by ultrasonic flaw detector or radiographic flaw detector: the parameters of the flaw detector are correctly set according to the operating instructions, and it is moved along the weld for inspection. By monitoring the inspection results displayed by the instrument, it can be determined whether there are defects in the weld, mark the location of the defects, accurately locate the problematic weld, grind the problematic weld area to a clean surface, remove the original welding residue or defects, and perform repair welding or heat treatment. Ensure that the correct welding materials and parameters are used to ensure the quality of the repaired weld. After the weld is repaired, the weld is inspected again using an ultrasonic flaw detector or radiographic flaw detector to ensure that the quality of the repaired weld meets the requirements.

[0041] In this embodiment, in step S4, the welding current is 110-140A. When the current is lower than 110A, it is easy to weaken the penetration of the weld, resulting in failure of complete melting and connection of the welding material, thereby affecting the quality and strength of the weld. When the current is higher than 140A, it is easy to cause excessive melting and penetration of the welding material, which may cause the weld to become too deep or too wide, thereby affecting the welding quality and appearance of the weld, increasing the amount of slag generated, resulting in difficulty in effectively removing the slag during the welding process, and may leave impurities around the weld, affecting the welding quality. The voltage is 18V.

[0042] In more detail, in this embodiment, before welding in step S4, a martensitic heat-resistant steel groove is prepared, the groove is a Y-shaped groove, the groove angle is 60 degrees to 90 degrees, the gap is 2 to 3 mm, and the blunt edge is 1 to 1.5 mm.

[0043] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A welding method for martensitic heat-resistant steel of a reheat boiler, characterized in that: The steps include: S1. Clean the end of the boiler module that needs to be welded, use an appropriate solvent to clean the surface of the welding area, and remove the oil and dirt on the surface; S2. Use a grinding wheel or abrasive disc to grind the surface of the welding area to remove rust and oxides to ensure a smooth surface; S3. Place the boiler module on a movable temporary support, measure it with a laser rangefinder, and make adjustments to ensure the module is aligned; S4, welding the boiler modules in groups of two to form a plurality of welded assemblies, and measuring and aligning them again by means of a laser rangefinder. During welding, the welding temperature is monitored in real time by means of a temperature sensor, and the welding temperature is between 500°C and 1000°C; S5. Weld the welding components together to form a reheat boiler, observe with the naked eye whether deformation occurs, and further measure with a measuring instrument; S6. After the welding part of the reheat boiler has cooled down, measure it again with the measuring instrument to check whether deformation occurs.

2. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: In step S1, the solvent is an acetone solvent or an alcohol solvent, which is loaded into a spraying device and sprayed onto the welding area to clean the welding area multiple times.

3. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: In step S2, if there are scratches or dents on the surface of the welding area, use a grinding tool to repair it to ensure that the surface of the welding area is flat, and use a clean rag or detergent to thoroughly wipe the surface of the welding area.

4. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: In step S3, the welding area of ​​the boiler module is preheated at a heating temperature of 200° C. to reduce deformation and residual stress during welding and ensure the performance of the welded joint.

5. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: In step S3, the placed boiler module is subjected to flaw detection by an ultrasonic flaw detector or a radiographic flaw detector, and a movable support is used as a temporary support to facilitate adjustment of the position of the boiler module.

6. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: In step S4, during welding, a clamp or a supporting structure may be used to align and fix the two modules, and a temporary support may be fixed at the same time to prevent the two modules from being misaligned during welding.

7. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: In step S4 and step S5, during welding, argon arc welding process is first used for positioning welding. After positioning welding is completed, after confirming that there are no defects, welding is started along the module welding area close to the inner wall. The thickness of the weld is 1 / 3 of the wall thickness of the martensitic heat-resistant steel, and then filling welding is performed.

8. The method for welding martensitic heat-resistant steel for a reheat boiler according to claim 1, characterized in that: After welding is completed, the weld is inspected by ultrasonic flaw detector or X-ray flaw detector, and the problematic weld is cut and re-grinded.

9. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: In step S4, the welding current is 110-140A and the voltage is 18V.

10. A reheat boiler martensitic heat-resistant steel welding method according to claim 1, characterized in that: Before welding in step S4, a martensitic heat-resistant steel groove is prepared. The groove is a Y-shaped groove with a groove angle of 60 to 90 degrees, a gap of 2 to 3 mm, and a blunt edge of 1 to 1.5 mm.