CN110763818B - Method for testing space spiral bent pipe for heat exchanger - Google Patents

Abstract

The invention discloses a method for inspecting a space spiral bend for a heat exchanger, comprising the following steps: selecting a plurality of straight heat transfer pipes, butt welding to form a plurality of welded pipes, and each welded pipe has the same or different number of welded pipes Joints; non-destructive testing and physical and chemical inspection of the welded joints; a space spiral elbow is prepared, the welded joint is located in the elbow unit, and at least two of the space spiral elbows have at least 2 elbow units with the smallest helical diameter ; Non-destructive testing, X-ray residual stress testing, MgCl ₂ stress corrosion and micro-crack inspection for welded joints; X-ray residual stress testing, MgCl ₂ stress corrosion and micro-crack inspection for non-welded parts. The inspection method of the space spiral elbow used for the heat exchanger of the present invention can not only completely inspect the overall quality of the heat transfer pipe but also reduce the inspection cost to the greatest extent.

Description

Inspection method of space spiral elbow for heat exchanger

technical field

The invention relates to the technical field of pipe fitting inspection, in particular to a method for inspecting a space spiral elbow for a heat exchanger.

Background technique

Space spiral coil heat exchanger is a special shell-and-tube heat exchanger with compact structure, large heat transfer coefficient and wide application, mainly used in electric power, machinery, marine engineering and other fields. When the design space is limited and the U-shaped heat exchange tube cannot be placed or the fluid pressure drop in the heat transfer tube is required to be small, the unique structure and flow advantages of the space spiral coil will be highlighted.

Although the space spiral coil heat exchanger has unique advantages, it also has certain difficulties in manufacturing and inspection. For heat transfer tubes with larger helical diameters, it requires a straight tube of sufficient length for bending, but due to the influence of the straight tube equipment of the manufacturer, the straight tube of the required length cannot be produced, so it is necessary to pass two or more straight tubes. Pipe butt welds meet length requirements. After the spiral coil, the welded joint becomes the weakest part of the whole pipe. How to fully inspect the welded area and the overall spiral coil to meet the design and regulatory requirements is the main difficulty. In addition, the space spiral coil heat exchanger usually requires high safety level and is a key component. Before the official product is manufactured, it is necessary to carry out the process evaluation of the spiral coil to verify that the overall quality of the spiral coil manufactured by the supplier can meet the design requirements.

The spiral coil is generally made of UNS N06690 material (the American grade, which corresponds to the French grade NC30Fe), which is an austenitic high nickel-chromium-iron (Ni-Cr-Fe) alloy. This alloy has remarkable resistance to oxidation and stress corrosion, as well as high strength, excellent metallurgical stability and processing characteristics.

The general manufacturing process flow of the spiral coil in the prior art is: vacuum induction smelting→electroslag remelting→forging blanking→hot extrusion→rolling→rolled annealing→aging treatment→butt welding→space bending→nondestructive testing → Cleanliness inspection → Packaging.

The process evaluation of the spiral coil means that the manufacturer manufactures and inspects a certain number of heat transfer tubes according to the expected requirements before the formal mass production, and the manufacturing conditions should be the same as the formal production. Bending process evaluation is also a verification method usually used before mass production of heat exchanger tubes.

The existing technology and standards only mention the basic requirements of the bending process evaluation, and it is only the minimum requirements for the entire bending process evaluation. It is not enough to verify the overall quality and manufacturing stability of the pipe before mass production.

SUMMARY OF THE INVENTION

In view of this, in order to overcome the defects of the prior art and achieve the above purpose, the purpose of the present invention is to provide a method for inspecting a space spiral elbow for a heat exchanger, which improves the accuracy of inspection results and reduces inspection costs.

In order to achieve the above object, the present invention adopts the following technical scheme:

A method for inspecting a space spiral elbow for a heat exchanger, comprising the following steps:

Step 1): Select a plurality of straight heat transfer tubes, the length of each straight heat transfer tube satisfies at least one bending unit with a minimum helical diameter that can be bent, after the straight tube heat transfer tube is annealed in the rolling state and aged , butt-welding the selected straight heat transfer tubes to form a plurality of welded tubes, each of which has the same or different number of welded joints;

Step 2): perform non-destructive testing and physical and chemical inspection on all the welded joints in the welded pipe obtained in step 1);

Step 3): bending the welded pipe prepared in step 1) to obtain a space spiral bend with a minimum helical diameter, the space spiral bend has several bend units and welded joints, and the welded joint is located in the bend unit Inside. The control welded joint is located in the curved section of the elbow unit, and cannot be located in the transition section or straight pipe section of the space spiral elbow;

Step 4): carry out non-destructive testing, X-ray residual stress detection, MgCl ₂ stress corrosion and micro-crack inspection on the welded joints in the space spiral bend in step 3); non-welded seams in the space spiral bend in step 3) X-ray residual stress inspection, MgCl ₂ stress corrosion and micro-crack inspection were carried out on the parts.

Preferably, the straight heat transfer tubes in step 1) at least include the straight heat transfer tubes at the highest temperature point in the furnace and the straight tube heat transfer tubes at the lowest temperature in the rolling annealing or aging treatment. Wherein, the highest temperature point and the lowest temperature point are determined based on the measurement of furnace temperature uniformity, the furnace structure and the effective area of the heat treatment furnace, which are common knowledge of those skilled in the art.

Preferably, in step 1), each welded pipe is welded by not less than two straight heat transfer pipes.

Preferably, the inspection items of the non-destructive testing in steps 2) and 4) include penetration testing and radiographic testing.

More preferably, the physical and chemical inspection described in step 2) comprises the following steps:

a. Select the welded pipe with at least 2 welded joints for tensile test, the test items include room temperature tensile and high temperature tensile; the room temperature here is 18-28 ℃, and the high temperature is based on the value given by the purchaser or the designer. standard, usually greater than 50°C.

b. Select welded pipes with at least 2 welded joints for intergranular corrosion test;

c. Select the welded pipe with at least 2 welded joints for hardness inspection, and the inspection parts include the weld area, heat-affected zone and matrix area; the hardness inspection is measured by the Vickers hardness test method;

d. Select the welded pipe with at least one welded joint for metallographic inspection. The inspection items include microstructure test (internal and external surfaces 500X), grain size determination test and carbide distribution inspection test (internal and external surfaces and middle parts, 500X, 1000X). 500X and 1000X both represent multiples.

More preferably, the length of the sample used for the room temperature tensile test in the step a is at least 300mm, and the length of the sample used for the high temperature tensile test is at least 800mm. The length of the sample for intergranular corrosion test, hardness test, microstructure test, grain size determination test and carbide distribution test test shall be at least 20mm.

More preferably, the sample used for the intergranular corrosion test in the step b is detected in its transverse direction; The specimens for the carbide distribution inspection test are tested in their longitudinal direction. During testing, longitudinal and/or transverse sampling is generally specified for grain size, carbide distribution or inclusions, while axial and/or circumferential sampling is generally specified for residual stress detection.

Preferably, in the space helical bend obtained by bending in step 3), at least two space helical bends include no less than two bend units with the smallest helical diameter.

More preferably, in step 4), penetrant inspection, radiographic inspection, X-ray residual stress inspection, MgCl ₂ stress corrosion and micro-crack inspection are performed on the welded joint portion of the space spiral elbow with the smallest spiral diameter elbow unit; step 4) X-ray residual stress inspection, MgCl ₂ stress corrosion and micro-crack inspection are carried out on the non-welded parts of the space spiral elbow.

Further preferably, the X-ray residual stress detection test in the step 4) includes two directions, axial and circumferential, and the sample selected for X-ray residual stress detection should be complete with elbows and The elbow of the transition section, and the free end of the straight pipe section at both ends should be kept at least 200mm in length. The elbow refers to the part with the largest bending, that is, the place with the largest residual stress; the straight pipe is the initial pipe without any deformation; the part between the straight pipe and the curved pipe is called the transition section, that is, there is a little deformation, which can be understood as bending The area near the point or final bend.

The above minimum spiral diameter is the minimum diameter of the tube bundle determined during the design of the heat exchanger. The definition of the tube bundle is: a group of tubes of the same diameter arranged in an orderly manner according to a certain rule can be understood as a batch or a bundle of tubes of the same specification.

The above steps fully consider the manufacturing factors and use conditions in the sampling process. Surface residual stress detection test, etc., can comprehensively test the overall quality of the heat exchanger welding space elbow, verify the manufacturer's manufacturing ability and management ability, judge whether the quality of the heat transfer pipe meets the design and safety requirements, and ensure the reliability of the manufacturing quality. Repeatability, effectively reduce inspection items, and minimize inspection costs.

Compared with the prior art, the present invention has the advantages that the inspection method of the space spiral bend for a heat exchanger of the present invention performs non-destructive testing and physical and chemical inspection on the welded pipe before bending and the space spiral bend after bending. Testing, through reasonable evaluation of sampling and quality inspection methods, with limited inspection parts and inspection methods to verify the uniformity of the internal quality of the spiral elbow and the representativeness of the acceptance test, this inspection method can fully inspect the overall quality of the heat transfer pipe It can also reduce the cost of inspection to the greatest extent, is economical and applicable, and is suitable for promotion.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

1 is a schematic diagram of the manufacturing and inspection process flow of the space spiral elbow in the preferred embodiment of the present invention;

Fig. 2 is the schematic diagram of butt welding of sampling pipe after rolling annealing and aging treatment of straight pipe heat transfer pipe in a preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of the position of drawing sampling at room temperature on the sampling tube after the butt welding of the straight tube heat transfer tube in the preferred embodiment of the present invention;

FIG. 4 is a schematic diagram of the position of high-temperature stretching sampling on the sampling tube after the butt welding of the straight tube heat transfer tube in the preferred embodiment of the present invention;

5 is a schematic diagram of the sampling position of the intergranular corrosion on the sampling tube after the butt welding of the straight tube heat transfer tube in the preferred embodiment of the present invention;

6 is a schematic diagram of the sampling position of the hardness test on the sampling tube after the butt welding of the straight tube heat transfer tube in the preferred embodiment of the present invention;

7 is a schematic diagram of the sampling position for microstructure, grain size and carbide inspection on the sampling tube of the straight tube heat transfer tube after butt welding in the preferred embodiment of the present invention;

Fig. 8 is the schematic diagram of the space spiral elbow in the preferred embodiment of the present invention;

FIG. 9 is a schematic diagram of the sampling positions of the space spiral elbow with and without the welded joint in the preferred embodiment of the present invention.

Detailed ways

In order to make those skilled in the art better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described implementation Examples are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in FIG. 1 , the manufacturing process of the space spiral bend in this embodiment at least includes: rolling→rolled annealing→aging treatment→butt welding→nondestructive testing (penetration testing and radiographic testing)→physical and chemical inspection→space bend →Non-destructive testing (penetration testing and radiographic testing) →Physical and chemical inspection. Among them, the rolling annealing process is used to improve the performance of the heat transfer tube in terms of strength and toughness, and the aging treatment process is mainly used to improve the carbide distribution and corrosion resistance of the heat transfer tube.

The inspection method of the space spiral elbow for a heat exchanger of the present embodiment includes the following steps:

Step 1): Select a plurality of straight heat transfer tubes, the length of each straight heat transfer tube satisfies at least one bending unit with a minimum helical diameter that can be bent, after the straight tube heat transfer tube is annealed in the rolling state and aged , butt welding the selected straight heat transfer tubes to form a plurality of welded tubes, and each welded tube has the same or different number of welded joints.

Wherein, the straight-pipe heat transfer tube at least includes the straight-pipe heat-transfer tube located at the highest temperature point in the furnace and the straight-pipe heat-transfer tube located at the lowest temperature point during the rolling annealing or aging treatment. Wherein, the highest temperature point and the lowest temperature point are determined based on the measurement of furnace temperature uniformity, the furnace structure and the effective area of the heat treatment furnace, which are common knowledge of those skilled in the art.

Each welded pipe is welded by no less than 2 straight heat transfer pipes.

The above minimum spiral diameter is the minimum diameter of the tube bundle determined during the design of the heat exchanger. The definition of the tube bundle is: a group of tubes of the same diameter arranged in an orderly manner according to a certain rule can be understood as a batch or a bundle of tubes of the same specification. This is the common knowledge of those skilled in the art.

As shown in FIG. 2 , it is a schematic diagram of the butt welding of the sampling tube 10 after the rolling annealing and aging treatment of the straight heat transfer tube of the present invention. The sampling tube 10 is obtained by butt welding of two straight tube heat transfer tubes. The welded heat transfer tube consists of the weld zone, the heat affected zone and the base metal zone.

Step 2): perform non-destructive testing and physical and chemical inspection on all the welded joints in the welded pipe obtained in step 1). The inspection items of non-destructive testing include penetrant testing and radiographic testing.

Physical and chemical testing includes the following steps:

a. Select the welded pipe with at least 2 welded joints for tensile test. The test items include room temperature tensile and high temperature tensile. The room temperature here is 18-28°C, and the high temperature is based on the value given by the purchaser or the designer, usually greater than 50°C.

As shown in FIG. 3 , a room temperature tensile sample A1 is cut from the butt welded sampling tube 10 for the straight heat transfer tube. The axial length of A1 along the sampling tube 10 is 300 mm, and it straddles the base metal area, the thermal Influenced area and butt weld area.

As shown in FIG. 4 , a high-temperature tensile sample A2 is cut from the butt welded sampling tube 20 for the straight heat transfer tube. The axial length of A2 along the sampling tube 20 is 800 mm, and it straddles the base metal area, the thermal Influenced area and butt weld area.

In other embodiments, the length of the sample used for the room temperature tensile test is at least 300 mm, and the length of the sample used for the high temperature tensile test is at least 800 mm.

b. Select welded pipes with at least 2 welded joints for intergranular corrosion test.

As shown in FIG. 5 , the intergranular corrosion sample A3 is taken from the butt welded sampling tube 30 for the straight heat transfer tube. The axial length of A3 along the sampling tube 30 is at least 30 mm, spanning the heat affected zone and the butt welding. seam area.

c. Select the welded pipe with at least 2 welded joints for hardness test, the test parts include the weld area, heat affected zone and matrix area; the hardness test is measured by the Vickers hardness test method.

As shown in FIG. 6 , the hardness test sample A4 is cut from the butt welded sampling tube 40 for the straight heat transfer tube. The axial length of A4 along the sampling tube 40 is 70 mm, and it straddles the base metal area. area and butt weld area.

d. Select the welded pipe with at least one welded joint for metallographic inspection. The inspection items include microstructure test (internal and external surfaces 500X), grain size determination test and carbide distribution inspection test (internal and external surfaces and middle parts, 500X, 1000X). Among them, 500X and 1000X both represent multiples.

As shown in FIG. 7 , a test sample A5 for microstructure, grain size and carbide is taken from the butt welded sampling tube 50 for the straight heat transfer tube, and the axial length of A5 along the sampling tube 50 is 50 mm, and Across the base metal area, heat affected zone and butt weld area.

In other embodiments, the length of the sample used for intergranular corrosion test, hardness test, microstructure test, grain size determination test and carbide distribution test test is at least 20 mm. The sample used for the intergranular corrosion test in step b is tested in its transverse direction; the sample used in the grain size determination test in step d is used for testing in its longitudinal direction and transverse direction respectively, and is used for the carbide distribution inspection test. Take its longitudinal direction for detection. During testing, longitudinal and/or transverse sampling is generally specified for grain size, carbide distribution or inclusions, while axial and/or circumferential sampling is generally specified for residual stress detection, which is a common knowledge of those skilled in the art.

Step 3): bending the welded pipe prepared in step 1) to obtain a space spiral bend with a minimum helical diameter, the space spiral bend has several bend units and welded joints, and the welded joints are located in the bend unit. Control weld joints are located in the curved section of the elbow element, but not in the transition or free section of a space helical elbow. As shown in Figures 8 and 9.

Step 4): carry out non-destructive testing, X-ray residual stress detection, MgCl ₂ stress corrosion and micro-crack inspection on the welded joints in the space spiral bend in step 3); non-welded seams in the space spiral bend in step 3) X-ray residual stress inspection, MgCl ₂ stress corrosion and micro-crack inspection were carried out on the parts. The inspection items of non-destructive testing include penetrant testing and radiographic testing.

In this step, penetrant inspection, radiographic inspection, X-ray residual stress inspection, MgCl ₂ stress corrosion and micro-crack inspection are performed on the welded joints of the space spiral bend with the smallest spiral diameter bend unit; in step 4), the space spiral bend is inspected. X-ray residual stress inspection, MgCl ₂ stress corrosion and micro crack inspection are carried out on the non-welded parts of the pipe. Among them, the X-ray residual stress detection test includes two directions, axial and circumferential, and the sample selected for X-ray residual stress detection should be a complete elbow with elbow and transition section, and both ends should be The free end of the straight pipe section shall be kept at least 200mm in length.

As shown in Figure 8, it is a schematic diagram of a space spiral elbow. The entire coil includes characteristic points such as the starting point, the end point, the part with welded joints, the part without welded joints, the straight pipe section at both ends, the curved pipe unit, and the transition section between the straight pipe section and the curved pipe unit. Among them, the elbow refers to the part with the largest bending, that is, the place with the largest residual stress; the straight pipe is the initial pipe without any deformation; the part between the straight pipe and the curved pipe is called the transition section, that is, there is a little deformation, which can be understood as The area near the start or end bend.

As shown in Figure 9, the surface residual stress test is carried out for the elbow unit without welded joints. The sample A6 selected for X-ray residual stress detection should be a complete elbow with elbow and transition section. The same elbow unit with welded joints is used for surface residual stress detection. The sample A7 selected for X-ray residual stress detection should be a complete elbow with elbows and transition sections, that is, A6 has no welded joints. , while the A7 has welded joints, but the sampling sites for both are elbows and transitions. The specimen A8 at the starting point and the specimen A9 at the end point shall be complete elbows with elbows and transition sections, and the free end of the straight pipe section shall be kept at least 200mm in length.

The above steps fully consider the manufacturing factors and use conditions in the sampling process. Surface residual stress detection test, etc., can comprehensively test the overall quality of the heat exchanger welding space elbow, verify the manufacturer's manufacturing ability and management ability, judge whether the quality of the heat transfer pipe meets the design and safety requirements, and ensure the reliability of the manufacturing quality. Repeatability, effectively reduce inspection items, and minimize inspection costs.

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those who are familiar with the art to understand the content of the present invention and implement them accordingly, and cannot limit the scope of protection of the present invention with this. Equivalent changes or modifications made in the spirit and spirit should all be included within the protection scope of the present invention.

Claims (6)

1. the inspection method of space spiral elbow for heat exchanger, is characterized in that: comprise the steps: Step 1): select a plurality of straight pipe heat transfer pipes, perform rolling annealing and aging treatment on the selected straight pipe heat transfer pipes to form a plurality of welded pipes, and each welded pipe has the same or different numbers of For welded joints, the distance between adjacent welded joints can bend at least one elbow unit with a minimum helical diameter; Step 2): carry out non-destructive testing and physical and chemical inspection on the welded joints in the welded pipe obtained in step 1); Step 3): bending the welded pipe prepared in step 1) to obtain a space spiral bend with a minimum helical diameter, the space spiral bend has several bend units and welded joints, and the welded joint is located in the bend unit Inside; Step 4): carry out non-destructive testing, X-ray residual stress detection, MgCl ₂ stress corrosion and micro-crack inspection on the welded joints in the space spiral bend in step 3); non-welded seams in the space spiral bend in step 3) X-ray residual stress inspection, MgCl ₂ stress corrosion and micro crack inspection are carried out on the parts; In the space helical bend obtained by bending in step 3), at least two space helical bends contain no less than 2 bend units with a minimum helical diameter; In step 4), penetrant inspection, radiographic inspection, X-ray residual stress inspection, MgCl ₂ stress corrosion and microscopic crack inspection are performed on the welded joints of the space spiral elbow with the smallest spiral diameter elbow unit; in step 4), the space spiral X-ray residual stress inspection, MgCl ₂ stress corrosion and micro-crack inspection are carried out on the non-welded parts of the elbow; The straight heat transfer tubes described in step 1) at least include the straight heat transfer tubes at the highest temperature point in the furnace and the straight heat transfer tubes at the lowest temperature point in the rolled annealing or aging treatment; in step 1), each The welded pipe is welded by not less than 2 straight heat transfer pipes; The whole coiled pipe of the space spiral elbow includes the starting point, the ending point, the part with welded joint, the part without welded joint, the straight pipe section at both ends, the curved pipe unit, and the connection between the straight pipe section and the curved pipe unit. Transition; Among them, the surface residual stress test is carried out for the elbow unit without welded joints, and the sample selected for X-ray residual stress detection has no welded joints, which is a complete elbow with elbows and transition sections; The elbow unit of the joint is subjected to surface residual stress detection, and the sample selected for X-ray residual stress detection is a complete elbow with elbow and transition section, and has a welded joint; the bending point sample and The final bending point specimen is a complete elbow with an elbow and a transition section, and the free end of the straight section should be kept at least 200mm in length. 2. The inspection method of a space spiral elbow for a heat exchanger according to claim 1, wherein the inspection items of the non-destructive testing in step 2) and step 4) include penetration testing and radiographic testing. 3. the inspection method of a kind of heat exchanger space spiral elbow according to claim 1, is characterized in that: physical and chemical inspection described in step 2) comprises the steps: a. Select the welded pipe with at least 2 welded joints for tensile test, the test items include room temperature tensile and high temperature tensile; b. Select welded pipes with at least 2 welded joints for intergranular corrosion test; c. Select welded pipes with at least 2 welded joints for hardness inspection; d. Select the welded pipe with at least one welded joint for metallographic inspection. The inspection items include microstructure test, grain size determination test and carbide distribution inspection test. 4. the inspection method of a kind of heat exchanger space spiral elbow according to claim 3, is characterized in that: in step a, in order to carry out the sample length of room temperature tensile test is at least 300mm, in order to carry out high temperature tensile The length of the test sample is at least 800mm, and the length of the sample used for intergranular corrosion test, hardness test, microstructure test, grain size determination test and carbide distribution test in steps b, c, and d is at least 20mm. . 5. The inspection method of a space spiral elbow for a heat exchanger according to claim 3, characterized in that: in step b, the sample used for the intergranular corrosion test is taken from its lateral direction for detection; in step d, it is used for crystal The longitudinal direction and transverse direction of the sample for particle size determination test are respectively tested, and the longitudinal direction of the sample used for the carbide distribution inspection test is selected for detection. 6. The inspection method of a space spiral elbow for a heat exchanger according to claim 1, wherein the X-ray residual stress detection test in the step 4) includes two directions of the axial direction and the circumferential direction, so the The sample selected for X-ray residual stress testing should be a complete elbow with elbows and transition sections, and the free ends of the straight pipe sections at both ends should be kept at least 200mm in length.

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