Steel sleeve welding structure and welding method of directly-buried steam pipeline

Abstract

The invention discloses a welding structure and a welding method for a steel sleeve of a directly-buried steam pipeline. The welding structure comprises a working pipe assembly; a steel sleeve assembly; wherein the working pipe assembly and the steel sleeve assembly are coaxially arranged, and a welding seam between every two adjacent working pipe sections and a welding seam between every two adjacent steel sleeve sections are arranged in a staggered mode; the steel sleeve assembly is provided with a fixed area section, a compensator area section and a straight pipe area section. The method has the beneficial effects that through cooperative application of the split type joint coating and the dragging pipe joint coating, in actual welding, the total weld length of the steel sleeve joint coating is reduced, and the consumption of welding materials can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to a steel casing welding structure and a welding method for a directly buried steam pipeline. Background Art

[0002] As a core facility for urban heat transmission, the reliability of the welding structure of a directly buried steam pipeline is directly related to the safe operation of the pipe network. The traditional steel casing welding structure mostly adopts a segmented jointing process, and the conventional segmented jointing requires longitudinal extension welds, resulting in a large total length of the welds and a high stress concentration coefficient, which is prone to fatigue cracking under thermal cyclic loads. In view of this, the present invention proposes a steel casing welding structure and a welding method for a directly buried steam pipeline to solve the above problems. Summary of the Invention

[0003] The purpose of the present invention is to provide a steel casing welding structure and a welding method for a directly buried steam pipeline to solve the problems raised in the above background art.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A steel casing welding structure for a directly buried steam pipeline, characterized in that it includes:

[0006] A working pipe assembly; the working pipe assembly is composed of n sequentially connected working pipe segments (the 1st to the nth working pipe segments) through working pipe welds (H 12 , H 23 , …, H {(n-2)n-2} , H {(n-1)n} ) to form a continuous inner pipe, and the outer surface of the working pipe segment is coated with a heat insulation layer;

[0007] A steel casing assembly; the steel casing assembly is composed of m sequentially connected steel casing segments (the 1st to the mth steel casing segments) through steel casing welds (h 12 , h 23 , …, h {(m-2)m-1} , h {(m-1)m} ) to form an outer protective layer, and the inner surface of the steel casing segment is coated with an anti-corrosion layer;

[0008] Wherein, the number m of the steel casing segments is the number n of the working pipe segments plus 1, and n≥5, the working pipe assembly and the steel casing assembly are coaxially arranged, and the welds between adjacent working pipe segments and the welds between adjacent steel casing segments are arranged staggeredly;

[0009] Wherein, the steel casing assembly is provided with a fixed area segment, a compensator area segment and a straight pipe area segment, the fixed area segment is the 1st and the mth steel casing segments, the compensator area segment is the 2nd and the m - 1th steel casing segments, and the straight pipe area segment is the 3rd to the m - 2th steel casing segments;

[0010] The weld seam h 12 and the weld seam h {(m-1)m are both formed by splicing and welding with segmented steel casing clamps, and are segmented joint welds;

[0011] The weld seam h 23 、h 34 …、the weld seam h {(m-2)m-1} are all formed by towing and butt-welding adjacent steel casing segments, and are pipe-towing joint welds.

[0012] As an improvement to the above technical solution, the length of the working pipe section (the 1st to the nth) is the length of the corresponding steel casing section plus ΔL, and the value range of ΔL is 500 - 600 mm.

[0013] As an improvement to the above technical solution, the length of the (m - 1)th steel casing section in the compensator area section is (n - 3)ΔL;

[0014] The length of the pipe-towing joint weld satisfies L = πD, where D is the outer diameter of the steel casing.

[0015] As an improvement to the above technical solution, the steel casing clamp of the segmented joint weld is three 120° arc-shaped steel plates, which are spliced along the circumferential direction of the steel casing to form a complete circular weld;

[0016] The pipe-towing joint weld is towed and butt-jointed through temporary lugs and manual hoists arranged in the horizontal direction of the steel casing section.

[0017] As an improvement to the above technical solution, the thermal insulation layer is composed of a composite of aluminosilicate fiber felt and polyurethane foam layer, where the thickness of the aluminosilicate fiber felt is 30 - 50 mm, and the density of the polyurethane foam layer is 60 - 80 kg / m 3 ;

[0018] The anticorrosion layer is an epoxy coal tar pitch coating, and the dry film thickness ≥ 300 μm.

[0019] A welding method for the steel casing welding structure of a directly buried steam pipeline includes the following steps:

[0020] Step 1. Working pipe butt-welding:

[0021] The n working pipe sections (the 1st to the nth) are butt-welded in sequence to form weld seams (H 12 、H 23 、…、H {(n-1)n} ), and all weld seams are subjected to radiographic non-destructive testing;

[0022] Step 2. Working pipe thermal insulation joint:

[0023] On the outer surface of the exposed working pipe section, repair the joint insulation layer with the same material as the prefabricated pipe section insulation layer, and wrap the fireproof cloth outside the insulation layer. The width of the fireproof cloth at the segmented joint is ΔL + 200 mm, and the width of the fireproof cloth at the pipe-dragging joint is ΔL. Both are fixed by tying with iron wire;

[0024] Step 3: Welding of the segmented joint of the steel casing:

[0025] For the steel casing sections between the fixed area sections (the 1st and the mth steel casing sections) and the compensator area sections (the 2nd and the m - 1th steel casing sections), use segmented steel casing clamps to splice and weld to form segmented joint welds (h 12 、h {(m-1)m} );

[0026] Step 4: Welding of the pipe-dragging joint of the steel casing:

[0027] For the steel casing sections between the straight pipe area sections (the 3rd to the m - 2th steel casing sections), use temporary lugs and manual hoists to drag and align them, and weld to form pipe-dragging joint welds (h 23 、h 34 、…h {(m-2)(m-1)} );

[0028] Step 5: Detection and anti-corrosion of the steel casing welds:

[0029] Perform ultrasonic non-destructive testing on all steel casing welds. After passing the test, perform anti-corrosion treatment on the joint.

[0030] As an improvement of the above technical solution, in the step 3, when performing segmented joint welding, the steel casing clamps are installed piece by piece from the bottom upwards, and the overlapping length of each pipe clamp with the steel casing sections on both sides is not less than 100 mm.

[0031] As an improvement of the above technical solution, in the step 4, before performing pipe-dragging joint welding, adjust the coaxiality of the working pipe and the steel casing through a guiding roller type pipe support, and control the deviation within ±5 mm;

[0032] In the step 3 and step 4, the welding sequence of the segmented joint and the pipe-dragging joint is: first complete all the segmented joint weldings, and then perform the pipe-dragging joint welding;

[0033] In the step 4, the temporary lug is a Q235B steel plate with a thickness of 10 mm, welded on both sides of the steel casing section, and the center distance of the lug from the weld edge is not less than 200 mm.

[0034] As an improvement of the above technical solution, in the step 1, if the weld detection is unqualified, repair it according to the following repair steps:

[0035] (a) Defect reinspection and classification: The complementary methods of ray detection and ultrasonic detection are used to reinspect the defect location. When the ratio of defect depth to pipe wall thickness ≤ 0.1, it is determined as a surface defect that can be repaired by grinding; when the ratio of defect depth to wall thickness > 0.1, it is determined as a deep defect that needs to be repaired by welding.

[0036] (b) Defect removal: For surface defects, an angle grinder is used to grind to form a transition zone with a slope ≤ 1:4. For deep defects, the defective section is cut off and a V-shaped / U-shaped groove is prepared, and then it is cleaned to remove oil stains and oxide scales.

[0037] (c) Welding repair: Welding materials matching the working pipe section are selected, and the multi-layer and multi-pass welding process is used to complete the repair welding, controlling the interlayer temperature and cleaning the welding slag layer by layer.

[0038] (d) Post-repair heat treatment: A hydrogen removal treatment at 250 - 350 °C is carried out on the repaired area, and stress annealing outside the sensitization temperature range is performed on the repaired area.

[0039] (e) Repair verification: 100% ray / ultrasonic detection and a hydrostatic pressure test at 1.5 times the design pressure are carried out on the repaired area to confirm that there are no surface cracks. If there are cracks, repeat the above steps.

[0040] As an improvement of the above technical solution, in step five, if the weld inspection is unqualified, the following repair steps are carried out for repair:

[0041] (a) Defect reinspection and classification: The complementary methods of ray detection and ultrasonic detection are used to reinspect the defect location. When the ratio of defect depth to pipe wall thickness ≤ 0.1, it is determined as a surface defect that can be repaired by grinding; when the ratio of defect depth to wall thickness > 0.1, it is determined as a deep defect that needs to be repaired by welding.

[0042] (b) Defect removal: For surface defects, an angle grinder is used to grind to form a transition zone with a slope ≤ 1:4. For deep defects, the defective section is cut off and a V-shaped / U-shaped groove is prepared, and then it is cleaned to remove oil stains and oxide scales.

[0043] (c) Welding repair: Welding materials matching the steel casing section are selected, and the multi-layer and multi-pass welding process is used to complete the repair welding, controlling the interlayer temperature and cleaning the welding slag layer by layer.

[0044] (d) Post-repair heat treatment: A hydrogen removal treatment at 250 - 350 °C is carried out on the repaired area, and stress annealing outside the sensitization temperature range is performed on the repaired area.

[0045] (e) Repair verification: 100% ray / ultrasonic detection and a hydrostatic pressure test at 1.5 times the design pressure are carried out on the repaired area to confirm that there are no surface cracks. If there are cracks, repeat the above steps.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] By limiting the number of steel casing segments m to be one more than the number of working pipe segments n (m = n + 1, and n ≥ 5), the welds of adjacent working pipes and the welds of the steel casings are arranged with an axial offset, effectively dispersing the axial stress concentration of the pipeline. The length of the compensator area section adopts a specific proportional relationship of (n - 2)ΔL, enabling the thermal displacement compensation amount to form a dynamic match with the weld spacing, and effectively extending the service life of the pipeline;

[0048] In the fixed area sections (the 1st and mth sections) and the compensator area sections (the 2nd and m - 1th sections), split - type steel casing clamps are used for welding, overcoming the problem of alignment deviation of traditional integral casings in complex pipe sections, and significantly improving the alignment accuracy. For the straight pipe area sections (the 3rd to m - 2th sections), the drag - welding process is adopted, combined with temporary lugs and guide - roller - type pipe supports, shortening the single - joint alignment time, significantly improving the efficiency compared with the traditional split - type process. Moreover, through the collaborative application of split - type joint compensation and pipe - dragging joint compensation, in actual welding, the total weld length of the steel casing joint is reduced, effectively reducing the consumption of welding materials. Brief Description of the Drawings

[0049] Figure 1 It is a schematic structural diagram of the present invention;

[0050] Figure 2 It is a schematic structural diagram of the working pipe assembly of the present invention;

[0051] Figure 3 It is a schematic position diagram of the working pipe assembly and the steel casing assembly of the present invention;

[0052] Figure 4 It is a schematic cross - sectional diagram of the working pipe section and the steel casing section of the present invention;

[0053] Figure 5 It is Figure 1 a schematic position diagram of the weld h in

[0054] Figure 6 It is Figure 2 a schematic position diagram of the weld H in

[0055] Figure 7 It is a schematic position diagram of the weld F of the split - type steel casing clamp splicing welding in the prior art.

[0056] In the figure: 10. Steel casing assembly; 20. Working pipe assembly; 30. Thermal insulation layer; 40. Anticorrosion layer. Detailed Embodiments

[0057] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0058] Embodiment:

[0059] As Figures 1-7 shown, this embodiment proposes a welded structure of a steel casing for a directly buried steam pipeline, including:

[0060] A working pipe assembly 20; the working pipe assembly 20 is formed by n sequentially connected working pipe segments (the 1st to the nth working pipe segments) through working pipe welds (H 12 , H 23 , …, H {(n-2)n-2} , H {(n-1)n} ) to form a continuous inner pipe, and the outer surface of the working pipe segment is coated with a heat insulation layer 30;

[0061] A steel casing assembly 10; the steel casing assembly 10 is formed by m sequentially connected steel casing segments (the 1st to the mth steel casing segments) through steel casing welds (h 12 , h 23 , …, h {(m-2)m-1} , h {(m-1)m} ) to form an outer protective layer, and the inner surface of the steel casing segment is coated with an anti-corrosion layer 40;

[0062] Among them, the number m of the steel casing segments is the number n of the working pipe segments plus 1, and n≥5. The working pipe assembly 20 and the steel casing assembly 10 are coaxially arranged, and the welds between adjacent working pipe segments and the welds between adjacent steel casing segments are arranged staggeredly;

[0063] Among them, the steel casing assembly 10 is provided with a fixed area section, a compensator area section, and a straight pipe area section. The fixed area section is the 1st and the mth steel casing segments, the compensator area section is the 2nd and the m-1th steel casing segments, and the straight pipe area section is the 3rd to the m-2th steel casing segments;

[0064] The weld h 12 and the weld h {(m-1)m are both formed by splicing and welding with a split steel casing clamp, and are split patch welds;

[0065] The welds h 23 , h 34 …, the welds h {(m-2)m-1} are all formed by butt welding adjacent steel casing segments in tow, and are tow pipe patch welds.

[0066] In this embodiment, by limiting the number of steel casing sections m to the number of working pipe sections n plus 1 (m=n+1, and n≥5), the adjacent working pipe welds and the steel casing welds are arranged in an axially staggered manner, which effectively disperses the axial stress concentration of the pipeline. The length of the compensator section adopts a specific proportional relationship of (n-2)ΔL, so that the thermal displacement compensation amount and the weld spacing form a dynamic match, which can effectively extend the service life of the pipeline;

[0067] The fixed section (sections 1 and m) and the compensator section (sections 2 and m-1) are welded with piece-type steel casing clamps, which overcomes the problem of matching deviation of traditional integral casing in complex pipe sections and significantly improves the matching accuracy. The straight pipe section (sections 3 to m-2) adopts a drag welding process, combined with temporary pull ears and guide roller-type pipe supports, which shortens the single patching time and significantly improves the efficiency compared with the traditional piece-type process. In addition, through the coordinated application of piece-type patching and drag pipe patching, in actual welding, the total weld length of the steel casing patching is reduced, which can effectively reduce the consumption of welding materials.

[0068] Specifically, the length of the working pipe section (the 1st to the nth) is the length of the corresponding steel casing section plus ΔL, and the value range of ΔL is 500-600 mm.

[0069] In this embodiment, by precisely controlling ΔL, the patching section of the working pipe insulation layer 30 and the prefabricated pipe section form an axial overlap of ≥200mm (when ΔL≥500mm), eliminating the thermal bridge effect at the joint of the insulation layer 30 caused by dimensional deviation in traditional processes.

[0070] Specifically, the length of the m-1th steel casing section of the compensator region is (n-3)ΔL;

[0071] The length of the pipe-drag patching weld satisfies L=πD, where D is the outer diameter of the steel casing.

[0072] Specifically, the steel casing clamp of the split-piece patch weld is three 120° arc-shaped steel plates, which are spliced along the circumference of the steel casing to form a complete annular weld;

[0073] The pipe-drag patching weld is dragged and assembled by means of temporary pulling ears and manual hoists arranged in the horizontal direction of the steel casing section.

[0074] In this embodiment, three 120° arc steel plates are spliced circumferentially to form an annular weld, and the angle difference of a single arc is ≤0.5°, so that the radial gap between the pipe clamp and the steel casing section is uniform;

[0075] Through the temporary pulling ear and manual hoist traction system, combined with the guide roller type pipe support, the straight pipe section assembly speed is increased, thereby effectively improving the welding efficiency.

[0076] Specifically, the thermal insulation layer 30 is composed of a composite of aluminosilicate fiber felt and polyurethane foam layer, where the thickness of the aluminosilicate fiber felt is 30 - 50 mm and the density of the polyurethane foam layer is 60 - 80 kg / m 3 ;

[0077] The anti-corrosion layer 40 is an epoxy coal tar pitch coating with a dry film thickness ≥ 300 μm.

[0078] In this embodiment, through the above materials, technical problems such as the collapse of the thermal insulation layer 30, the peeling of the anti-corrosion layer 40, and the interface failure that have long existed in the directly buried pipeline are solved, achieving triple breakthroughs in energy efficiency, durability, and economy in the high-temperature steam pipeline project, and having significant industrial application value.

[0079] A welding method for the welded structure of the steel casing of a directly buried steam pipeline includes the following steps:

[0080] Step 1. Welding of the working pipe group:

[0081] Arrange and weld n working pipe segments (the 1st to the nth) in sequence to form welds (H 12 、H 23 、…、H {(n-1)n} ), and perform radiographic non-destructive testing on all welds;

[0082] Step 2. Thermal insulation repair of the working pipe:

[0083] Repair and insulate the outer surface of the exposed working pipe segment with the thermal insulation layer 30, and the material is the same as that of the prefabricated pipe segment. Wrap a fireproof cloth outside the thermal insulation layer 30. The width of the fireproof cloth at the patchwork joint is ΔL + 200 mm, and the width of the fireproof cloth at the drag pipe joint is ΔL. Both are fixed by tying with iron wires;

[0084] Step 3. Welding of the steel casing patchwork joint:

[0085] For the steel casing segments between the fixed area segment (the 1st and the mth steel casing segments) and the compensator area segment (the 2nd and the m - 1th steel casing segments), use a split steel casing clamp to splice and weld to form split joint welds (h 12 、h {(m-1)m} );

[0086] Step 4. Welding of the steel casing drag pipe joint:

[0087] For the steel casing segments between the straight pipe area segments (the 3rd to the m - 2nd steel casing segments), use a temporary lug and a manual hoist to drag and assemble, and weld to form drag pipe joint welds (h 23 、h 34 、…h {(m-2)(m-1)} );

[0088] Step 5. Detection and anti-corrosion of the steel casing welds:

[0089] All steel casing welds shall be subjected to ultrasonic non-destructive testing. After passing the test, anti-corrosion treatment shall be carried out at the joint area.

[0090] In this embodiment, through the synergistic effect of innovative structural design and process optimization, the comprehensive improvement of the welding quality, construction efficiency and service performance of the directly buried steam pipeline is realized: the combined process of segmented joint (circumferential splicing of three 120° arc-shaped steel plates) and pipe-dragging joint (πD continuous weld) is adopted, which reduces the total length of the weld and the stress concentration coefficient. Combined with the dynamic misalignment arrangement of the working pipe and the steel casing (m = n + 1) and the precise dimension control of the compensator area section (n - 3)ΔL, the thermal displacement compensation efficiency is increased by 42%; the innovative gradient thermal insulation structure (30 - 50 mm of aluminum silicate fiber felt + 60 - 80 kg / m 3 ) and the compatibility of the epoxy coal tar anti-corrosion coating (≥300 μm) reduce the heat loss of the pipeline and the cathodic protection current density. Combined with the staged non-destructive testing (radiography + ultrasonic testing) and the differential fireproof cloth wrapping process (segmented joint ΔL + 200 mm / pipe-dragging joint ΔL), zero burn-out of the thermal insulation layer and reduction of the weld defect rate are achieved, the comprehensive construction efficiency is improved, and the life-cycle cost is reduced. In the field of long-distance high-temperature steam transportation, systematic technical problems such as weld cracking, thermal insulation failure, and high corrosion rate are overcome, with significant technological progress and industrial application value.

[0091] Specifically, in step three, when welding the segmented joint, the steel casing clamps are installed piece by piece from the bottom upwards, and the overlapping length of each clamp with the two adjacent steel casing sections is not less than 100 mm.

[0092] Specifically, in step four, before welding the pipe-dragging joint, the coaxiality of the working pipe and the steel casing is adjusted by the guiding roller type pipe support, and the deviation is controlled within ±5 mm.

[0093] Specifically, in steps three and four, the welding sequence of the segmented joint and the pipe-dragging joint is: first complete the welding of all segmented joints, and then carry out the welding of the pipe-dragging joint.

[0094] Specifically, in step four, the temporary lugs are Q235B steel plates with a thickness of 10 mm, welded on both sides of the steel casing section, and the center distance of the lugs from the weld edge is not less than 200 mm.

[0095] Specifically, in step one, if the weld inspection is unqualified, the repair shall be carried out according to the following repair steps:

[0096] (a) Defect reinspection and classification: The location of the defect is reinspected by using a complementary method of radiographic testing and ultrasonic testing. When the ratio of the defect depth to the pipe wall thickness ≤ 0.1, it is determined as a surface defect that can be repaired by grinding; when the ratio of the defect depth to the wall thickness > 0.1, it is determined as a deep defect that requires repair by welding.

[0097] (b) Defect removal: For surface defects, an angle grinder is used to grind to form a transition zone with a slope ≤ 1:4. For deep defects, the defective section is cut off and a V-shaped / U-shaped groove is prepared, and it is cleaned to remove oil stains and oxide scales.

[0098] (c) Welding repair: Welding consumables matching the working pipe section are selected, and the repair welding is completed by using a multi-layer and multi-pass welding process, controlling the interlayer temperature and cleaning the welding slag layer by layer.

[0099] (d) Post-repair heat treatment: A hydrogen removal treatment at 250 - 350 °C is carried out on the repaired area, and stress annealing outside the sensitization temperature range is performed on the repaired area.

[0100] (e) Repair verification: 100% radiographic / ultrasonic testing and a hydrostatic test at 1.5 times the design pressure are carried out on the repaired area to confirm no surface cracks. If there are cracks, repeat the above steps.

[0101] Specifically, in step five, if the weld inspection is unqualified, the repair shall be carried out according to the following repair steps:

[0102] (a) Defect reinspection and classification: The location of the defect is reinspected by using a complementary method of radiographic testing and ultrasonic testing. When the ratio of the defect depth to the pipe wall thickness ≤ 0.1, it is determined as a surface defect that can be repaired by grinding; when the ratio of the defect depth to the wall thickness > 0.1, it is determined as a deep defect that requires repair by welding.

[0103] (b) Defect removal: For surface defects, an angle grinder is used to grind to form a transition zone with a slope ≤ 1:4. For deep defects, the defective section is cut off and a V-shaped / U-shaped groove is prepared, and it is cleaned to remove oil stains and oxide scales.

[0104] (c) Welding repair: Welding consumables matching the steel casing section are selected, and the repair welding is completed by using a multi-layer and multi-pass welding process, controlling the interlayer temperature and cleaning the welding slag layer by layer.

[0105] (d) Post-repair heat treatment: A hydrogen removal treatment at 250 - 350 °C is carried out on the repaired area, and stress annealing outside the sensitization temperature range is performed on the repaired area.

[0106] (e) Repair verification: 100% radiographic / ultrasonic testing and a hydrostatic test at 1.5 times the design pressure are carried out on the repaired area to confirm no surface cracks. If there are cracks, repeat the above steps.

[0107] In this embodiment, based on the welding structure and welding method described above, the following data comparison is carried out. This comparison includes the working pipe assembly 20 and the steel casing assembly 10, and a comparison is made between the conventional segmented joint and the combined joint in this embodiment;

[0108] In the working pipe assembly 20, n takes the value of 7, in the steel casing assembly 10, m takes the value of 8, and ΔL takes the value of 600 mm;

[0109] The specification of the working pipe section in the working pipe assembly 20: Φ630×10 mm;

[0110] The specification of the steel casing section in the steel casing assembly 10: Φ1220×10 mm;

[0111] The fixed area section, namely the first steel casing section and the eighth steel casing section, has a length of 1.5 m;

[0112] The compensator area section, namely the second steel casing section and the seventh steel casing section, has a length of 3 m;

[0113] The straight pipe area section, namely the third steel casing section to the sixth steel casing section, has a length of 12 m;

[0114] Table 1 shows the comparison data between the conventional segmented joint and the combined joint.

[0115]

[0116] The description of the data calculation in the above table:

[0117] The total length of the welds for the conventional segmented joint technology:

[0118] 9462 mm×7 = 66234 mm

[0119] The formula for the single joint weld:

[0120] 2πD + 3ΔL = 2×3.14×1220 + 3×600 = 9462 mm

[0121] (In the formula, 2πD is the circumferential welds on both sides, and 3ΔL is the total length of the longitudinal joints between the three arc-shaped steel plates, with each extending by ΔL)

[0122] The total length of the welds in this embodiment (segmented + pipe-dragging joint):

[0123] 9462 mm×2 (segmented) + 3831 mm×6 (pipe-dragging type) = 18924 + 22986 = 41910 mm

[0124] The formula for the single joint weld of the pipe-dragging type: πD = 3.14×1220 = 3831 mm

[0125] The reduction ratio of the welds:

[0126] (66,234 - 41910) / 66,234 × 100% = 36.7%

[0127] Through the above data comparison, it can be concluded that in this embodiment, through the combination optimization of segmented and pipe-dragging joint repair, the weld length is reduced by 36.7%, the construction efficiency is significantly improved, the comprehensive cost is reduced, and the pipe-dragging joint repair can avoid the deformation of pipe clamps, the weld gap is uniform, and the welding qualification rate is significantly improved. It is especially suitable for long-distance directly buried pipelines and projects passing through complex sections, and has high engineering popularization value.

[0128] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A steel casing welding structure for a directly buried steam pipeline, characterized in that: Including: Working pipe assembly (20); the working pipe assembly (20) is composed of n successively connected working pipe segments (the 1st to the nth working pipe segments) through working pipe welds (H 12 , H 23 , …, H {(n-2)n-2} , H {(n-1)n} ) to form a continuous inner pipe, and the outer surface of the working pipe segment is coated with a heat insulation layer (30); Steel casing assembly (10); the steel casing assembly (10) is formed by m successively connected steel casing segments (the 1st to the mth steel casing segments) through steel casing welds (h 12 , h 23 , …, h {(m-2)m-1} , h {(m-1)m} ) to form an outer protective layer, and an anti-corrosion layer (40) is coated on the inner surface of the steel casing segment; Wherein, the number of steel casing segments m is equal to the number of working pipe segments n plus 1, and n≥5. The working pipe assembly (20) and the steel casing assembly (10) are coaxially arranged, and the welds between adjacent working pipe segments and the welds between adjacent steel casing segments are staggered. Wherein, the steel casing assembly (10) is provided with a fixed area section, a compensator area section, and a straight pipe area section. The fixed area section is the 1st and the mth steel casing segments, the compensator area section is the 2nd and the m - 1th steel casing segments, and the straight pipe area section is the 3rd to the m - 2th steel casing segments. The weld h 12 and the weld h {(m-1)m are both formed by splicing and welding with segmented steel casing clamps, which are segmented joint welds; The weld seam h 23 、h 34 …, the weld seam h {(m-2)m-1} are all formed by dragging and butt-welding adjacent steel casing pipe segments, and are the weld seams for pipe dragging and joint repair.

2. The steel casing welding structure of the directly buried steam pipeline according to claim 1, characterized in that: The length of the working pipe segments (the 1st to the nth) is the length of the corresponding steel casing segment plus ΔL, and the value range of ΔL is 500 - 600mm.

3. The steel casing welding structure of a directly buried steam pipeline according to claim 1, characterized in that: The length of the m - 1th steel casing segment in the compensator area section is (n - 3)ΔL. The length of the drag pipe joint weld satisfies L = πD, where D is the outer diameter of the steel casing.

4. A steel casing welding structure for a directly buried steam pipeline according to claim 1, characterized in that: The steel casing clamp of the segmented joint weld is three 120° arc-shaped steel plates, which are spliced along the circumferential direction of the steel casing to form a complete circular weld. The drag pipe joint weld is dragged and assembled by means of temporary lugs and manual hoists arranged horizontally on the steel casing segment.

5. A steel casing welding structure for a directly buried steam pipeline according to claim 1, characterized in that: The thermal insulation layer (30) is composed of a composite of aluminosilicate fiber felt and a polyurethane foam layer, where the thickness of the aluminosilicate fiber felt is 30 - 50 mm and the density of the polyurethane foam layer is 60 - 80 kg / m 3 ; The anti-corrosion layer (40) is an epoxy coal tar pitch coating, and the dry film thickness is ≥300μm.

6. A welding method for a steel casing welding structure of a directly buried steam pipeline according to any one of claims 1-5, characterized in that: Including the following steps: Step 1: Assembly and welding of the working pipe Successively butt-weld n working pipe sections (the 1st to the nth) to form welds (H 12 , H 23 , …, H {(n-1)n} ), and perform radiographic non-destructive testing on all welds; Step 2: Thermal insulation joint repair of the working pipe On the outer surface of the exposed working pipe segment, repair the thermal insulation layer (30). The material is the same as that of the prefabricated pipe segment thermal insulation layer, and a fireproof cloth is wrapped outside the thermal insulation layer (30). The width of the fireproof cloth at the segmented joint is ΔL + 200mm, and the width of the fireproof cloth at the drag pipe joint is ΔL. Both are fixed by wire bundling. Step 3: Segmented joint welding of the steel casing For the steel casing segments between the fixed area segments (the 1st and the mth steel casing segments) and the compensator area segments (the 2nd and the (m - 1)th steel casing segments), split-type steel casing clamps are used for splicing and welding to form split-type joint welds (h 12 , h {(m-1)m} ); Step 4: Drag pipe joint welding of the steel casing For the steel casing segments between the straight pipe sections (the 3rd to the (m - 2)th steel casing segments), they are assembled by pulling with temporary lugs and manual hoists, and welded to form the pipe pulling repair welds (h 23 , h 34 , … h {(m-2)(m-1)} ); Step 5: Weld inspection and anti-corrosion of the steel casing All steel casing segment welds are subjected to ultrasonic non-destructive testing. After passing the test, anti-corrosion treatment is carried out at the joint.

7. The welding method of the steel casing welding structure of a directly buried steam pipeline according to claim 6, characterized in that: In the above Step 3, during segmented joint welding, the steel casing clamps are installed one by one from the bottom upwards, and the overlapping length of each pipe clamp with the two adjacent steel casing segments is not less than 100mm.

8. The welding method of the steel casing welding structure of a directly buried steam pipeline according to claim 6, characterized in that: In the above Step 4, before drag pipe joint welding, the coaxiality of the working pipe and the steel casing is adjusted by a guide roller type pipe support, and the deviation is controlled within ±5mm. In the above Steps 3 and 4, the welding sequence of the segmented joint and the drag pipe joint is: first complete all the segmented joint welds, and then carry out the drag pipe joint welding. In the above Step 4, the temporary lug is a Q235B steel plate with a thickness of 10mm, which is welded on both sides of the steel casing segment, and the center of the lug is not less than 200mm away from the weld edge.

9. The welding method of the steel casing welding structure of a directly buried steam pipeline according to claim 6, characterized in that: In the above Step 1, if the weld inspection is unqualified, repair shall be carried out according to the following repair steps: (a) Defect re-inspection and classification: The position of the defect is re-inspected by a complementary method of ray detection and ultrasonic detection. When the ratio of the defect depth to the pipe wall thickness ≤0.1, it is determined as a surface defect that can be repaired by grinding; when the ratio of the defect depth to the wall thickness >0.1, it is determined as a deep defect that needs to be repaired by welding. (b) Defect removal: Use an angle grinder to grind the surface defects to form a transition zone with a slope ≤ 1:

4. For deep defects, cut off the defective section and prepare a V-shaped / U-shaped groove, and clean it to remove oil stains and oxide scales; (c) Welding repair: Select welding materials matching the working pipe section, and complete the repair welding using the multi-layer and multi-pass welding process, control the interlayer temperature and clean the welding slag layer by layer; (d) Post-repair heat treatment: Perform a hydrogen removal treatment at 250 - 350 °C on the repair area, and perform a stress annealing outside the sensitization temperature range on the repair area; (e) Repair verification: Conduct 100% radiographic / ultrasonic testing and a hydrostatic test at 1.5 times the design pressure on the repair area to confirm no surface cracks. If there are cracks, repeat the above steps.

10. The welding method of the steel casing welding structure of a directly buried steam pipeline according to claim 6, characterized in that: In the fifth step above, if the weld inspection is unqualified, repair it according to the following repair steps: (a) Defect re-inspection and classification: Re-inspect the defect location using the complementary method of radiographic testing and ultrasonic testing. When the ratio of the defect depth to the pipe wall thickness ≤ 0.1, it is determined as a surface defect that can be ground and repaired; when the ratio of the defect depth to the wall thickness > 0.1, it is determined as a deep defect that requires repair welding; (b) Defect removal: Use an angle grinder to grind the surface defects to form a transition zone with a slope ≤ 1:

4. For deep defects, cut off the defective section and prepare a V-shaped / U-shaped groove, and clean it to remove oil stains and oxide scales; (c) Welding repair: Select welding materials matching the steel casing section, and complete the repair welding using the multi-layer and multi-pass welding process, control the interlayer temperature and clean the welding slag layer by layer; (d) Post-repair heat treatment: Perform a hydrogen removal treatment at 250 - 350 °C on the repair area, and perform a stress annealing outside the sensitization temperature range on the repair area; (e) Repair verification: Conduct 100% radiographic / ultrasonic testing and a hydrostatic test at 1.5 times the design pressure on the repair area to confirm no surface cracks. If there are cracks, repeat the above steps.

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