An annular gasket material for pipe welding

Abstract

This invention belongs to the field of welding auxiliary materials technology, specifically relating to a ring-shaped gasket material for pipe welding. From the radial inner side to the radial outer side, it comprises a fusible support layer, a high-temperature resistant skeleton layer, a flexible bonding layer, and an active metallurgical layer. The fusible support layer is composed of a eutectic salt of sodium chloride, potassium chloride, and sodium silicate, which softens or partially melts at 650℃-750℃; the high-temperature resistant skeleton layer is a continuous alumina fiber woven and sintered mesh structure; the flexible bonding layer is a composite pressed layer of graphite worms and aluminosilicate fiber felt; and the active metallurgical layer is a coating layer containing titanium dioxide, cryolite, ferrosilicon powder, ferromanganese powder, and aluminum powder. This gasket addresses three practical engineering problems in pipe circumferential welding: assembly rigidity, high-temperature load-bearing capacity, and curved surface fit. Through the progressive and overlapping effect of the four-layer structure, it allows for a certain degree of asynchronous response among the layers, accommodating a certain range of assembly tolerances and welding parameter fluctuations. After welding, there are virtually no obstructions remaining inside the pipe, and the weld root is well-formed.

Description

Technical Field

[0001] This invention belongs to the technical field of welding auxiliary materials, specifically relating to an annular gasket material for pipe welding. Background Technology

[0002] In the installation of long-distance oil and gas pipelines, chemical plants, and ship pipelines, the circumferential welding of pipeline joints is a critical process that determines the safety of the project. For small and medium-diameter pipelines, welders cannot enter the interior to weld due to the pipe diameter limitation, and can only complete single-sided welding and double-sided forming from the outside. In this case, a backing must be placed at the root of the weld on the inner wall of the pipeline to support the molten pool, prevent the weld melt from flowing down, isolate the air, and provide a support for the formation of the weld on the back side.

[0003] In practical engineering, the inventors discovered that the core difficulty faced by pipe circumferential weld gaskets is not a single performance deficiency, but rather three interrelated but not synchronous engineering problems: First, during the room temperature assembly stage, the gasket needs to have sufficient rigidity to resist deformation and collapse during the pushing process. However, this rigidity requirement will turn into a negative factor after the welding temperature rises. If the rigid structure cannot make way in time, it will hinder the close contact between the bonding layer and the pipe wall.

[0004] Secondly, during the high-temperature welding stage, the gasket needs to continuously bear the pressure of the molten pool and prevent the weld melt from flowing down. However, at this time, the outer layer of the gasket must form an effective fit with the curved surface of the pipe wall. But in actual engineering conditions, the inner wall of the pipe to be welded is not an ideal cylindrical surface. It is inevitable that there are dimensional deviations and surface defects such as pipe diameter ellipticity, local rust pits, and machining marks. Conventional rigid or semi-rigid gaskets cannot adapt to the above deviations. It is very easy for the molten pool to leak due to the gasket not fitting tightly with the pipe wall, which in turn forms weld beads, incomplete penetration, or poor formation on the back of the weld.

[0005] Third, in the post-weld cleaning stage, the ideal technical effect in the industry is that the gasket can be completely removed, with no solid residue left inside the pipe. However, in actual welding operations, due to the influence of various working parameters such as fluctuations in welding heat input, changes in welding position (flat / vertical / overhead welding), and differences in shielding gas atmosphere, the response of each functional layer of the gasket to the welding thermal cycle has obvious temporal differences. This can easily lead to problems such as local solid residues in the gasket, uneven slag coverage on the back of the weld, and even obstruction of the pipe's flow.

[0006] Currently available welding gaskets are mostly designed to address only one of the three interdependent technical challenges mentioned above, failing to meet the operational requirements of the entire pipeline welding process and making it difficult to adapt to the complex and ever-changing working conditions on-site. They all exhibit insurmountable technical defects in practical applications, as detailed below: While copper gaskets have high thermal conductivity, which can create a rapid cooling effect on the weld pool, they are prone to localized fusion and adhesion with the pipe base material and weld metal under high-temperature welding conditions. This not only causes copper to seep into the weld metal, significantly reducing the low-temperature impact toughness of the weld joint, a problem particularly prominent in the welding of high-strength oil and gas long-distance pipelines, but also makes it difficult to remove the copper gasket smoothly from small- to medium-diameter long-distance pipelines after welding. Leaving it inside the pipe can create a permanent obstruction, failing to meet the requirements of subsequent operations such as pipeline balling and cleaning. Removing the gasket from the pipe after welding is almost impossible in small- to medium-diameter long pipe sections, while leaving it inside causes obstruction.

[0007] Ceramic gaskets have high temperature resistance, but they are also brittle. During welding, localized thermal shock can easily cause them to crack and peel off, with debris entering the molten pool and forming slag inclusions. As a rigid body, ceramic gaskets are difficult to fit perfectly against the curved surface of the pipe wall. Even slight ellipticity or rust pits in the pipe wall can lead to leakage in the molten pool and the formation of weld beads.

[0008] Flexible gaskets, such as fiberglass tape and graphite tape, are soft and easy to fit, but their temperature resistance is severely insufficient. The molten pool temperature of steel is about 1500℃, while the softening point of fiberglass is only 600℃-800℃, and graphite oxidizes in air at 500℃. During welding, these materials burn instantly and cannot support the molten pool.

[0009] The inventors also noted during the experiments that different batches of pipes exhibited varying degrees of internal corrosion due to differing storage conditions; and that different welding positions (flat welding, vertical welding, overhead welding) significantly impacted the stress state of the gasket. These engineering variables necessitate that the gasket design possess a certain tolerance capability, rather than merely performing well under ideal conditions. Summary of the Invention

[0010] The purpose of this invention is to provide an annular gasket material for pipe welding.

[0011] To achieve the above objectives, the present invention provides the following technical solution: A ring-shaped gasket material for pipe welding includes, from the radial inner side to the radial outer side, a fusible support layer, a high-temperature resistant skeleton layer, a flexible bonding layer, and an active metallurgical layer. The fusible support layer is a ring-shaped layer of salt eutectic material composed of sodium chloride, potassium chloride and sodium silicate. The ratio of the materials allows the layer to soften or partially melt within the range of 650℃-750℃, forming a flowing or semi-flowing state during the welding process. The high-temperature resistant skeleton layer is a mesh structure layer woven from continuous alumina fibers and sintered with silica sol, with a porosity of 40%-60%. The flexible bonding layer is a compressed layer composed of graphite worms and aluminum silicate fiber felt, with a compression rate of 30%-50%. The active metallurgical layer is composed of dry powder components and a binder; based on the total mass of the dry powder components (100%), the proportions of each component are: cryolite 10%-25%, ferrosilicon powder 5%-15%, ferromanganese powder 3%-12%, aluminum powder 2%-8%, with the balance being rutile titanium dioxide; the binder accounts for 15%-25% of the total mass of the active metallurgical layer. The wall thickness of the fusible support layer is 1.5-3.0 mm, the thickness of the high-temperature resistant skeleton layer is 0.8-1.5 mm, the thickness of the flexible bonding layer is 1.0-2.0 mm, and the thickness of the active metallurgical layer is 0.3-0.8 mm.

[0012] Furthermore, the mass percentage of sodium chloride in the fusible support layer is 55%-70%, the mass percentage of potassium chloride is 20%-35%, and the mass percentage of sodium silicate is 5%-10%.

[0013] Furthermore, the porosity of the high-temperature resistant skeleton layer is 40%-60%, and the diameter of the continuous alumina fiber is 8-15μm.

[0014] Furthermore, the mass ratio of graphite worms to aluminosilicate fiber felt in the flexible bonding layer is 1:0.3-0.6, and the density of the flexible bonding layer is 0.8-1.2 g / cm³. 3 .

[0015] Furthermore, the binder is one or both of silica sol and sodium silicate.

[0016] Furthermore, the gasket material has a closed circular structure with an outer diameter 0.1-0.3 mm smaller than the inner diameter of the pipe to be welded.

[0017] Furthermore, the gasket material is an open ring structure with an axially extending open slot, the opening width is 2-5mm, and the outer diameter is 0.5-1.0mm larger than the inner diameter of the pipe to be welded.

[0018] Furthermore, after the open ring structure is installed into the pipe to be welded, the high-temperature resistant skeleton layer and the flexible bonding layer are in a radially compressed state.

[0019] Beneficial effects of this invention: 1. The fusible support layer is made of a eutectic salt system of sodium chloride, potassium chloride, and sodium silicate, and its rigidity at room temperature is sufficient to meet the requirements for pushing and positioning. After welding begins, the heat of the electric arc gradually softens or melts it, and most of it decomposes and escapes or transforms into a peelable thin layer of residue before and after the root pass is completed. Compared with pure metal supports, there are basically no obstructions remaining inside the pipe after welding.

[0020] 2. The skeleton layer is made of continuous alumina fiber woven together and then sintered with silica sol. The temperature resistance of the alumina fiber itself meets the temperature requirements of the molten steel pool, and the silica sol sintering gives the fiber nodes a certain bonding strength. The woven structure replaces the integral sintered ceramic block. When subjected to welding thermal shock, even if local fiber nodes loosen, the whole block will not peel off, reducing the risk of slag inclusions.

[0021] 3. The bonding layer utilizes the compression and resilience properties of graphite worms and the temperature resistance and erosion resistance of aluminosilicate fiber felt to adapt to actual surface conditions such as pipe wall ellipticity, rust pits, and tool marks. Under most pipe wall conditions, it can ensure reliable contact between the active metallurgical layer and the pipe wall, reducing the probability of molten pool leakage.

[0022] 4. The active metallurgical layer melts during welding to form a protective slag that covers the root weld pool, effectively isolating it from air. The ferrosilicon and ferromanganese components it contains can, to some extent, compensate for the loss of silicon and manganese elements during welding, while the exothermic deoxidation of aluminum powder aids in root fusion. The slag can usually be easily removed after welding.

[0023] 5. The four-layer structure plays a progressive role in the assembly, welding, and forming stages: the support layer is responsible for initial rigidity, the skeleton layer is responsible for structural continuity throughout the process, the bonding layer is responsible for compensating for shape deviations, and the metallurgical layer is responsible for molten pool protection and composition adjustment. There is functional overlap between the layers, and no single layer is completely relied upon to achieve all the functions of a certain stage, thus providing a certain degree of tolerance to engineering fluctuations.

[0024] 6. Available in both closed and open ring designs to accommodate different pipe diameters. The open ring's tension comes from the braid's elasticity and compression resilience, eliminating the need for additional pressure fittings and simplifying on-site operations. (See attached diagram for details.) Figure 1 This is a schematic diagram of the cross-sectional structure of the annular gasket material of the present invention.

[0025] Figure 2 This is a schematic diagram of a closed circular ring structure.

[0026] Figure 3 This is a schematic diagram of an open-ring structure.

[0027] Figure 4 This is a schematic diagram showing the state of the open ring structure after it has been installed into the pipe to be welded.

[0028] Marked in the image: 1. Effluent support layer; 2. High-temperature resistant skeleton layer; 3. Flexible bonding layer; 4. Active metallurgical layer; 5. Annular gasket material; 6. Pipe to be welded; 7. Opening gap. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to these embodiments. Unless otherwise specified, the raw materials used in the embodiments are all commercially available industrial-grade products.

[0030] Example 1 This embodiment describes the preparation of a closed annular gasket for butt welding of 20# steel pipes with an inner diameter of 89mm and a wall thickness of 6mm. The structure is described in [reference needed]. Figure 1 and Figure 2 .

[0031] I. Preparation of the fusible support layer 1 Take 650g of sodium chloride, 300g of potassium chloride, and 50g of sodium silicate, and mix them evenly in a graphite crucible. Place the crucible in a resistance furnace and heat it to 730℃, holding it at that temperature for 20 minutes until the material is completely melted. During this time, stir slowly twice with a graphite rod to promote homogenization of the composition. After the melt has stood for 5 minutes to remove air, pour it into a steel ring mold preheated to 200℃. The mold cavity dimensions correspond to an inner diameter of 77mm, an outer diameter of 83mm, and a wall thickness of 3.0mm for the support layer. After casting, allow it to cool naturally to room temperature before demolding to obtain the fusible support layer 1.

[0032] A small sample was taken and measured using a differential scanning calorimeter. The softening initiation temperature was 718℃, and the sample completely melted. Cross-sectional observation of the sample showed a uniform and dense salt eutectic structure.

[0033] II. Preparation of High-Temperature Resistant Skeleton Layer 2 Continuous alumina fibers with a diameter of 10μm, an Al2O3 content of not less than 99.5%, and a single filament tensile strength of not less than 1.8GPa are selected. A ring-shaped mesh skeleton is woven using a four-step method on a three-dimensional braiding machine. The number of braiding yarns is 96, the braiding angle is 35°, and the braiding density is 10 yarns / cm. After completion, the skeleton layer 2 has an inner diameter of 83mm, an outer diameter of 85.4mm, and a thickness of 1.2mm.

[0034] A 25% alkaline silica sol with SiO2 particle size of 10-15 nm and pH of 9.0-9.5 was used. The woven skeleton was immersed in the silica sol under a vacuum of -0.08 MPa for 30 minutes, and then the excess sol was drained off. The immersed skeleton was placed in an oven and dried at 80°C for 4 hours. After drying, the skeleton was transferred to a high-temperature sintering furnace, heated to 900°C at a rate of 5°C / min, held at that temperature for 2 hours, and then cooled to room temperature with the furnace. After sintering, a continuous and dense SiO2 coating layer was formed on the surface of the alumina fibers, and the fiber nodes were firmly bonded. The resulting high-temperature resistant skeleton layer 2 had a thickness of 1.2 mm and an average porosity of approximately 52% as measured by Archimedes' displacement method. Thermal shock tests were conducted on the same batch of skeleton layer samples, with local heating to approximately 1500°C using a propane flame and holding for 30 seconds. No through cracks were found during visual inspection.

[0035] III. Preparation of Flexible Adhesive Layer 3 Take 100g of expandable graphite (50 mesh, expansion rate 200ml / g), place it in a muffle furnace preheated to 920℃ for 5 seconds to expand instantaneously, and quickly remove it to obtain graphite worms with a bulk density of approximately 0.012g / cm³. 3 .

[0036] Take 50g of aluminosilicate fiber felt, use it at 1260℃, with a density of 0.16g / cm³. 3 After being loosened, the mixture was combined with the aforementioned graphite worms in a mixer at 60 rpm for 10 minutes. The mixture was then evenly spread into the cavity of a ring mold and pressed at 5 MPa for 30 seconds to form a ring layer with an inner diameter of 85.4 mm, an outer diameter of 87.8 mm, and a thickness of 1.2 mm. After demolding, the density of the flexible adhesive layer 3 was measured to be 0.98-1.05 g / cm³. 3 It belongs to the medium-to-high density fiber composite felt category, and its compression behavior is close to that of a semi-rigid porous material. According to GB / T10653, the compression rate is 43% and the resilience is 86%.

[0037] IV. Preparation of the active metallurgical layer 4 Take 45g of rutile titanium dioxide (purity not less than 98%, 325 mesh); 15g of cryolite (industrial grade, 200 mesh); 8g of ferrosilicon powder (Si content 75%, 200 mesh); 5g of ferromanganese powder (Mn content 80%, 200 mesh); and 3g of aluminum powder (purity not less than 99%, 200 mesh). Mix the above materials in a V-type mixer for 20 minutes to obtain a mixed powder.

[0038] 24g of sodium silicate solution (modulus 2.8, concentration 40%) was used as a binder and mixed with the above-mentioned powder in a mixer to form a uniform slurry. The outer circumferential surface of the flexible bonding layer 3 was cleaned, and the slurry was evenly coated onto the surface with a brush, with the coating thickness controlled to approximately 0.7mm for the wet film. After coating, the surface was placed in an oven and dried and cured at 60℃ for 2 hours. After drying, the actual thickness of the active metallurgical layer 4 was measured to be 0.45mm. The mass percentages of each component were: rutile titanium dioxide 45%, cryolite 15%, ferrosilicon powder 8%, ferromanganese powder 5%, aluminum powder 3%, and binder 24%.

[0039] V. Four-layer composite The fusible support layer 1 is placed on the innermost side, the high-temperature resistant skeleton layer 2 is fitted onto the outside of the support layer 1, and then the flexible bonding layer 3 with the active metallurgical layer 4 is fitted onto the outside of the skeleton layer 2, with the active metallurgical layer 4 facing outwards. A small amount of silica sol with a modulus of 3.2 is applied between the contact surfaces of each layer for bonding and positioning. The layers are then dried in an oven at 80°C for 1 hour to allow them to bond together as a whole. The final outer diameter of the annular gasket material 5 is 88.7 mm, slightly smaller than the inner diameter of the pipe 6 to be welded by 0.3 mm, and the axial width is 25 mm. Its cross-sectional structure is shown in [details omitted]. Figure 1 The overall structure is a closed circular ring. Figure 2 .

[0040] VI. Welding Applications The pipe to be welded, 6, is made of 20# steel with dimensions of Ф89×6mm. It has a V-shaped bevel with a 60° bevel angle, a 1.0mm blunt edge, and a 3.0mm assembly gap. The aforementioned gasket material 5 is pushed into the pipe from the end; the push is smooth and without obstruction. The gasket is then adjusted to the center of the bevel using a positioning rod.

[0041] The welding method employed manual tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) for the fill and cover passes. The root pass welding parameters were: welding current 90A, argon flow rate 8L / min, tungsten electrode diameter 2.4mm, and ER50-6 welding wire with a diameter of 2.5mm. During the welding process, it was observed that when the root pass was completed approximately 1 / 4 of the circumference, the molten support layer 1 began to soften and deform; after the root pass was completed, the support layer 1 had essentially melted away, and the high-temperature resistant skeleton layer 2 and the flexible bonding layer 3 adhered further to the pipe wall under the heat-affected zone of welding. Upon completion of the root pass, no obvious support layer residue was observed upon visual inspection inside the pipe; a small amount of thin white layer was visible adhering to the inner side of the skeleton, which easily detached with a light tap. The fill pass welding current was 115A, and the cover pass welding current was 110A, using E5015 welding wire with a diameter of 3.2mm.

[0042] Post-weld inspection of the weld was performed at 100% radiographic level, and the result was rated as Grade I according to NB / T47013.2 standard, with no defects such as incomplete penetration, lack of fusion, porosity, or slag inclusions. The weld root was uniformly formed, with a reinforcement height of 0.5-0.8 mm. Mechanical property tests were conducted on samples: the tensile strength of the welded joint was 482 MPa, and the measured strength of the base metal was 465 MPa; in the bending test, the mandrel diameter was 18 mm, and the bending angle was 180°, with no cracks on the tensile surface; the impact absorption energy of the weld zone at -20℃ was 72 J, 68 J, and 85 J. Chemical composition analysis of root weld samples revealed a Mn content of 1.32% and a Si content of 0.26%, indicating that Mn and Si elements were replenished compared to the original composition of the welding wire.

[0043] Example 2 This embodiment describes the preparation of an open annular gasket for butt joint welding of Q345B steel pipes with an inner diameter of 325mm and a wall thickness of 10mm. See the attached structure. Figure 3 and Figure 4 .

[0044] The preparation process for each layer is basically the same as in Example 1, with the following adjustments: The fusible support layer 1 is made of 600g sodium chloride, 350g potassium chloride, and 50g sodium silicate, with a melting temperature of 720℃. The corresponding wall thickness of the casting mold is 2.55mm, resulting in an inner diameter of 315.2mm and an outer diameter of 320.3mm.

[0045] High-temperature resistant skeleton layer 2: alumina fiber diameter 12μm, weaving density 9 fibers / cm, impregnated with silica sol and sintered at 900℃, thickness 1.0mm, porosity 48%.

[0046] Flexible bonding layer 3: Graphite worms to aluminum silicate fiber felt in a mass ratio of 1:0.5, pressed to a thickness of 1.2 mm, with a density of 1.05 g / cm³. 3 .

[0047] Activated metallurgical layer 4: 40g rutile titanium dioxide, 18g cryolite, 10g ferrosilicon powder, 8g ferromanganese powder, 4g aluminum powder, 20g silica sol as binder, solid content 30%, coating thickness 0.6mm. After drying, a small number of micro-cracks were visible on the surface of activated metallurgical layer 4, and no coating peeling was observed during welding.

[0048] The initial outer diameter of the four-layer composite gasket under mold constraints is 325.9 mm. A 3 mm wide opening slit 7 is cut along the axial direction using a thin-blade milling cutter to form an open ring structure. After cutting, the gasket expands radially due to the release of internal stress, and the measured outer diameter in the free state is approximately 326 mm.

[0049] Welding Application: The pipe to be welded (6) is made of Q345B steel, with dimensions of Ф325×10mm, a V-groove angle of 60°, a blunt edge of 1.5mm, and an assembly gap of 3.5mm. The open-ring gasket (5) is manually radially compressed and then inserted into the pipe, utilizing its elastic restoring force generated by its expansion tendency to tighten the pipe wall. Endoscopic observation shows that the gasket is tightly fitted to the pipe wall around its entire circumference, with no visible gaps, thus effectively preventing leakage of the molten pool during welding.

[0050] CO2 gas shielded welding was used. The root pass current was 150A and voltage was 21V, and the fill and cover passes current was 190A and voltage was 25V. The welding wire was ER50-6 with a diameter of 1.2mm, and the shielding gas flow rate was 18L / min. During welding, the erosive support layer 1 completely melted away before the root pass was completed. After welding, the bonding layer thickness was found to be approximately 0.1-0.2mm thinner than before welding, which was determined to be due to a small amount of oxidation of the graphite component in the oxidizing atmosphere. However, the bonding layer remained intact overall, without any peeling or perforation. Post-weld radiographic inspection was Class I qualified, and the weld root was smoothly formed. The joint tensile strength was 538MPa, the bending test was qualified, and the average impact absorption energy of the weld zone at 0℃ was 94J.

[0051] Example 3 Based on the active metallurgical layer 4 formulation of Example 1, samples were prepared using sodium silicate and silica sol as binders, respectively, and welding comparisons were conducted.

[0052] Sodium silicate sample: the same as the scheme used in Example 1. The active metallurgical layer slurry has good coating properties. After drying, it is firmly bonded to the flexible bonding layer. After welding, the slag forms a thin shell that continuously covers the surface. After being tapped, the entire piece falls off.

[0053] Silica sol sample: The active metallurgical layer 4 formulation is the same as in Example 1, except that the binder is replaced with 20g of silica sol, and an appropriate amount of water is added to adjust the slurry viscosity. After coating and drying, the surface of the active metallurgical layer has slight microcracks, which do not affect the function during welding and use, and the slag removal is good. However, the silica sol binder sample did not show significant moisture absorption and softening after being stored in a humid environment for 7 days, while the sodium silicate sample was slightly sticky on the surface under the same conditions, requiring drying before use.

[0054] The mechanical properties of the welded joints using the two adhesive methods are not significantly different, and both meet the application requirements.

[0055] Comparative Example 1 A commercially available copper annular gasket, with an outer diameter of 88.5 mm and a width of 25 mm, was used for pipe butt welding under the same welding conditions as in Example 1. After welding, the copper gasket fused and adhered to the weld root in multiple places. However, after repeated and forceful tapping from the other end, the gasket was eventually deformed and removed, leaving obvious scratches on the inner wall of the pipe. Radiographic testing revealed intermittent copper infiltration at the weld root, and spectral analysis showed that the local Cu content at the root reached 0.9%. The tensile strength of the joint was 451 MPa, and the average impact absorption energy of the weld zone at -20°C was 43 J, which was lower than that in Example 1.

[0056] Comparative Example 2 A commercially available alumina-based ceramic gasket was used, consisting of multiple arc-shaped ceramic blocks assembled into a ring with an outer diameter of 89 mm, and welded under the same conditions as in Example 1. During welding, a crisp cracking sound could be heard as the ceramic blocks cracked, and multiple pieces of flaked ceramic fragments were found inside the pipe after welding. Radiographic testing revealed multiple point-like slag inclusions at the weld root, rated as Class III according to NB / T47013.2. The joint's tensile strength was 465 MPa, and the average impact energy was 50 J.

[0057] Comparative Example 3 The same fusible support layer 1, high-temperature resistant skeleton layer 2, and flexible bonding layer 3 as in Example 1 were used, but without the active metallurgical layer 4. The flexible bonding layer was in direct contact with the pipe wall. Welding was performed under the same conditions. The weld root formation was acceptable, but the surface oxide color was darker. The tensile strength of the joint was 474 MPa, and the average impact absorption energy of the weld zone at -20°C was 55 J, which was about 30% lower than that in Example 1. Energy dispersive spectroscopy analysis showed that the oxygen content of the root weld was about twice that of Example 1.

[0058] Comparative Example 4 The gasket was prepared according to the process in Example 1, except that the formulation of the fusible support layer 1 was changed to 800g of sodium chloride and 200g of potassium chloride, without adding sodium silicate. The softening initiation temperature of the support layer was measured to be 630℃, and the complete melting temperature was 795℃, exceeding the range of 650℃-750℃. Under the welding conditions of Example 1, the support layer was not completely eroded when the root pass was completed, and some solid residue remained attached to the inner side of the high-temperature resistant skeleton layer, which needed to be removed by compressed air after welding. This indicates that the addition of sodium silicate plays a role in controlling the eutectic erosion temperature range.

[0059] Comparative Example 5 Referring to Example 1, the mass ratio of graphite worms to aluminosilicate fiber felt in the flexible bonding layer 3 was adjusted to 1:0.1 (i.e., graphite content was approximately 91%), with a density of 0.65 g / cm³. 3 Welding was performed under CO2 gas shielded welding conditions. Post-weld inspection revealed that the bonding layer thickness was reduced by approximately 0.6 mm compared to the initial thickness, with through-holes appearing in localized areas. Slight oxidation was observed on the back weld at the corresponding locations. This indicates that when the graphite ratio is too high, significant volume loss occurs under an oxidizing atmosphere, affecting the integrity of the bonding layer.

[0060] The results of the above embodiments and comparative examples are summarized in Table 1 below.

[0061] Table 1: Summary of Results for Examples and Comparative Examples

[0062] Note: The impact energy of Example 1 is the test value at -20℃, Example 2 is the test value at 0℃, and Comparative Examples 1, 2, 3, 4, and 5 are all test values ​​at -20℃.

[0063] As can be seen from the data in the table, Embodiments 1 and 2 of the present invention are superior to the comparative examples in terms of assembly convenience, post-weld residue cleaning, weld non-destructive testing level, and joint mechanical properties, verifying the comprehensive effect of the four-layer composite structure and its specific material composition in engineering applications. Meanwhile, the results of Comparative Examples 4 and 5 show that when the material ratio of each layer exceeds the defined range, the post-weld residue of the gasket, the integrity of the bonding layer, and the weld protection effect will be identifiablely affected, thus demonstrating, from the opposite perspective, that the parameter range defined in this application has practical engineering significance.

[0064] It should be noted that the above embodiments are only used to explain the technical concept of the present invention and are not intended to limit the scope of protection. Any adjustments made by those skilled in the art, after reading this specification, to the specific proportions, thicknesses, and preparation process parameters of each layer of material based on common knowledge and conventional experimental methods, without departing from the essential spirit of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A ring-shaped gasket material for pipe welding, characterized in that, From the radial inner side to the radial outer side, it includes a fusible support layer (1), a high-temperature resistant skeleton layer (2), a flexible bonding layer (3), and an active metallurgical layer (4). The fusible support layer (1) is a ring-shaped layer of salt eutectic material composed of sodium chloride, potassium chloride and sodium silicate. Its ratio makes the layer soften or partially melt in the range of 650℃-750℃, forming a flowing or semi-flowing state during the welding process. The high-temperature resistant skeleton layer (2) is a mesh structure layer woven from continuous alumina fibers and sintered with silica sol, with a porosity of 40%-60%. The flexible bonding layer (3) is a pressed layer composed of graphite worms and aluminum silicate fiber felt, with a compression rate of 30%-50%. The active metallurgical layer (4) is composed of dry powder components and a binder; based on the total mass of the dry powder components as 100%, the proportions of each component are: cryolite 10%-25%, ferrosilicon powder 5%-15%, ferromanganese powder 3%-12%, aluminum powder 2%-8%, and the balance is rutile titanium dioxide; the mass of the binder accounts for 15%-25% of the total mass of the active metallurgical layer (4); The wall thickness of the fusible support layer (1) is 1.5-3.0 mm, the thickness of the high temperature resistant skeleton layer (2) is 0.8-1.5 mm, the thickness of the flexible bonding layer (3) is 1.0-2.0 mm, and the thickness of the active metallurgical layer (4) is 0.3-0.8 mm.

2. The annular gasket material for pipe welding according to claim 1, characterized in that, The mass percentage of sodium chloride in the fusible support layer (1) is 55%-70%, the mass percentage of potassium chloride is 20%-35%, and the mass percentage of sodium silicate is 5%-10%.

3. The annular gasket material for pipe welding according to claim 1, characterized in that, The porosity of the high-temperature resistant skeleton layer (2) is 40%-60%, and the diameter of the continuous alumina fiber is 8-15μm.

4. The annular gasket material for pipe welding according to claim 1, characterized in that, The mass ratio of graphite worms to aluminum silicate fiber felt in the flexible bonding layer (3) is 1:0.3-0.6, and the density of the flexible bonding layer (3) is 0.8-1.2 g / cm³. 3 .

5. The annular gasket material for pipe welding according to claim 1, characterized in that, The binder is one or both of silica sol and sodium silicate.

6. The annular gasket material for pipe welding according to claim 1, characterized in that, The gasket material (5) is a closed ring structure with an outer diameter 0.1-0.3 mm smaller than the inner diameter of the pipe (6) to be welded.

7. The annular gasket material for pipe welding according to claim 1, characterized in that, The gasket material (5) is an open ring structure with an axially extending open slit (7) with an opening width of 2-5 mm and an outer diameter 0.5-1.0 mm larger than the inner diameter of the pipe to be welded (6).

8. The annular gasket material for pipe welding according to claim 7, characterized in that, After the open ring structure is installed into the pipe to be welded (6), the high temperature resistant skeleton layer (2) and the flexible bonding layer (3) are in a radially compressed state.

Images