Polyethylene composite wrapping tape and pipeline corrosion prevention method

Abstract

The invention belongs to the field of pipeline corrosion prevention, and particularly relates to a polyethylene composite wrapping tape and a pipeline corrosion prevention method. The polyethylene composite wrapping tape comprises a polyethylene base material and an adhesive layer which are compounded up and down, the upper surface of the polyethylene base material is flat, and the height of the lower surface of the polyethylene base material is reduced from the middle to the two ends in the tape width direction; the lower surface of the adhesive layer is flat, and the upper surface of the adhesive layer and the lower surface of the polyethylene base material are complementary in shape; an extrusion inclined surface is formed on the lower surface part corresponding to the wound and lapped end of the polyethylene base material, and the extrusion inclined surface extrudes the molten adhesive to flow and fill the lapped and non-lapped transition position of the subsequent winding during winding and lapping, so that the elevation difference of the lapped and non-lapped transition position is compensated. During winding and lap joint, the phenomenon of uneven appearance is avoided, generation of local hollowing at the edge position of the tape is reduced, and the quality of the anticorrosive coating of the polyethylene composite winding tape is further improved.

Description

Technical Field

[0001] The present invention belongs to the field of external anti-corrosion of buried steel pipelines and hot-bent elbows, and particularly relates to a polyethylene composite winding tape and a pipeline anti-corrosion method. Background Art

[0002] The polyethylene composite winding tape is used for the external anti-corrosion layer of pipeline straight sections and hot-bent elbows. During construction, the polyethylene winding tape is pre-wound on a mechanical winding machine and spirally wound onto a primer layer with a certain temperature under a certain tension. According to the analysis of the on-site construction of pipeline polyethylene composite winding tapes in recent years, when the polyethylene composite winding tape is wound on a steel pipe or elbow with a 50% overlap, it is very difficult to achieve an effective peel interface of more than 95% between the polyethylene composite winding tape and the epoxy powder coating. The effective peel interface is the effective coverage rate of the adhesive layer on the epoxy powder coating, which is an important aspect that needs to be improved in the overall anti-corrosion quality of the polyethylene composite winding tape external anti-corrosion layer.

[0003] There are two reasons for the low coverage rate of the peel interface: (1) Since the winding overlap amplitude is 50% - 55%, there is a sudden change in thickness at the overlap, and there are triangular voids in the cross-section at the overlap. Even in the molten state, the adhesive layer is difficult to fill, resulting in air pockets. The general characteristic of air pockets is that they penetrate along the overlap, and strip-shaped through-air pockets appear after the winding tape is peeled off. (2) During the winding process, the adhesive layer is also a process of exhausting air when it adheres to the bottom layer. In fact, the air cannot be completely exhausted, so some air is trapped between the adhesive layer and the bottom layer, forming irregular patchy air pockets.

[0004] The applicant previously disclosed a special-shaped tape for pipeline joint repair (i.e., a polyethylene composite winding tape, see the Chinese patent application with the publication date of October 22, 2024, and the publication number of CN118816030A). This polyethylene special-shaped tape is a two-layer structure formed by a polyethylene backing and an adhesive layer. The adhesive layer gradually thins from the middle to both sides, aiming to use the thick adhesive layer in the middle to flow to both sides in the molten state to achieve the purpose of filling air pockets.

[0005] The above-mentioned polyethylene special-shaped tape has improved the air pocket problem to a great extent compared with the traditional polyethylene composite tape. However, some new defects have also appeared during application. The reason is that the adhesive layer is in the shape of an arc, step, etc., with a thick middle and thin sides. After the adhesive layer contacts the primer layer with a relatively high temperature under tension winding, it cannot be evenly distributed to both sides according to the pre-designed shrinkage of the substrate. The substrate is a flat structure, and the uneven flow of the adhesive layer makes the shrinkage force of the substrate unstable under the heated state. After the adhesive layer is heated and melted and deformed, circumferential cross-sectional corrugations and internal local air pockets appear, resulting in an uneven state on the surface of the polyethylene composite winding tape anti-corrosion layer and affecting the appearance quality. Summary of the Invention

[0006] The object of the present invention is to provide a polyethylene composite winding tape, which solves the problems that the existing polyethylene composite tape is uneven in appearance due to the synergistic deformation with the adhesive layer under the heated state after spiral winding, and local air pockets will appear at the edge position of the tape.

[0007] The second object of the present invention is to provide a pipeline anti-corrosion method, which solves the problem that the anti-corrosion quality of the outer anti-corrosion layer of the existing polyethylene composite tape needs to be further improved.

[0008] In order to achieve the above first object, the technical solution adopted by the present invention is:

[0009] A polyethylene composite winding tape includes a polyethylene base material and an adhesive layer which are compounded up and down. The upper surface of the polyethylene base material is flat, and the lower surface decreases in height from the middle to both ends in the bandwidth direction; the lower surface of the adhesive layer is flat, and the upper surface is complementary in shape to the lower surface of the polyethylene base material; a pressing inclined surface is formed on a part of the lower surface corresponding to the wound and overlapped end of the polyethylene base material. When winding and overlapping, the pressing inclined surface presses the molten adhesive to flow and fill into the transition position between the lap and non-lap of the subsequent winding, compensating for the elevation difference at the transition position between the lap and non-lap.

[0010] The present invention belongs to an improved invention. By designing the flat surfaces of the upper and lower polyethylene base materials and the adhesive surface, and designing the bonding interface between the polyethylene base material and the adhesive as a special shape, that is, the bonding interface between the polyethylene base material and the adhesive (i.e., the lower surface of the polyethylene base material) is in the shape of being high in the middle and low on both sides. When winding and overlapping, the pressing inclined surface presses the molten adhesive to flow and fill into the transition position between the lap and non-lap of the subsequent winding, compensating for the elevation difference at this position; at the same time, since the upper and lower surfaces of the polyethylene composite winding tape are flat, there will be no uneven appearance phenomenon and the generation of local air pockets at the edge position of the tape is reduced, further improving the spiral winding quality.

[0011] In addition, when using a mechanical winding machine to wind the tape, the problem of unstable tension caused by the unevenness of the above-mentioned polyethylene special-shaped tape can be well solved, thereby further optimizing the winding stability and winding quality of the tape.

[0012] Preferably, the pressing inclined surface is an arc-shaped, oblique-linear or stepped shape that rises upward along the winding and overlapping direction. Further preferably, the lower surface of the polyethylene base material is symmetric in shape along its width center line.

[0013] Preferably, the maximum thickness of the polyethylene base material is 1.2 - 2.2 mm, and the maximum thickness of the adhesive layer is 0.5 - 1.4 mm; the total thickness of the polyethylene composite winding tape is 1.5 - 3.0 mm.

[0014] Preferably, the upper surface of the wound and overlapped end of the polyethylene substrate is trimmed to form a cut with an angle of 5-30° with the horizontal direction. Further preferably, the upper surface of the other end of the polyethylene substrate is trimmed to form a cut with an angle of 5-30° with the horizontal direction.

[0015] Preferably, the thickness of the substrate remaining after trimming is 0.2-0.8 mm.

[0016] Preferably, the width of the part with a reduced height on one side of the polyethylene substrate accounts for 10-50% of the total width of the substrate.

[0017] To achieve the second above-mentioned object, the technical solution adopted by the present invention is:

[0018] A pipeline anti-corrosion method includes the following steps:

[0019] (1) Coating a fusion-bonded epoxy powder coating on the surface of a bare pipe whose surface pretreatment reaches the specified effect before painting;

[0020] (2) Wrapping the above-mentioned polyethylene composite winding tape around the fusion-bonded epoxy powder coating whose temperature is higher than the melting point of the adhesive layer, and then heating and fusing the wound polyethylene composite winding tape;

[0021] (3) Cooling the heated and fused polyethylene composite winding tape with compressed air first, and then cooling and shaping it with water.

[0022] Based on the above structural design of the polyethylene composite winding tape, the pipeline anti-corrosion method of the present invention can further reduce the generation of drum formation during winding and overlapping, reduce the defects of the external anti-corrosion layer of the pipeline, avoid the infiltration of water vapor and ions, and improve the pipeline anti-corrosion quality.

[0023] Preferably, it is cooled with compressed air until the surface temperature is below 100°C, and then cooled and shaped with water. Description of the Drawings

[0024] Figure 1 It is a schematic structural diagram of the arc-shaped polyethylene composite winding tape of Embodiment 1 of the present invention;

[0025] Figure 2 It is a schematic structural diagram of the triangular polyethylene composite winding tape of another embodiment of the present invention;

[0026] Figure 3 It is a schematic structural diagram of the stepped polyethylene composite winding tape of another embodiment of the present invention;

[0027] Figure 4 It is a peeling photo after winding the polyethylene composite tape of CN118816030A;

[0028] Figure 5This is a photo of the polyethylene composite wrapping tape of the present invention after being peeled off;

[0029] Among them, 1-polyethylene substrate; 2-adhesive layer; 3-extruded end face; 4-first incision; 5-second incision. DETAILED DESCRIPTION

[0030] 1. Description of the preferred embodiment of the polyethylene composite wrapping tape of the present invention

[0031] In response to the problem that the polyethylene special-shaped tape involved in CN118816030A has unstable shrinkage force due to uneven flow distribution of the adhesive on the substrate, resulting in an uneven appearance and local hollowing at the edge of the tape, the inventors further optimized the structural design of the polyethylene composite wrapping tape, that is, when the polyethylene substrate and the adhesive layer are compounded in the up and down directions, the upper surface of the polyethylene substrate and the lower surface of the adhesive layer are flat (that is, the upper and lower surfaces of the tape appear flat), and the bonding interface between the polyethylene substrate and the adhesive layer is designed to be high in the middle and low on both sides in the bandwidth direction, that is, the polyethylene substrate as a whole is thick in the middle and thin on both sides, and the adhesive layer is bonded to the polyethylene substrate, and the bonding interface between the adhesive layer and the polyethylene substrate presents a complementary characteristic, that is, the adhesive layer as a whole is thin in the middle and thick on both sides. This structural design offers specific advantages during wrapping and lap joints: the adhesive layer melts and flows upon contact with the pipe primer. For example, with a 50% overlap, the compressive force provided by the wrapping and lap joint allows the polyethylene substrate's structural design to evenly distribute the molten adhesive to the overlapping transition area (the transition between the overlap and non-overlap of the subsequent wrapping process), thus resolving the problem of filling the overlapping transition area. Furthermore, the polyethylene composite wrapping tape boasts a smooth top and bottom surface, eliminating the problems of unevenness causing gaps and the resulting localized hollowing (small, localized) at the peeling interface.

[0032] When wrapping the polyethylene composite wrapping tape, the last wrap will overlap one end of the previous wrap. For example, when spirally wrapping from left to right, the last wrap will overlap the right end of the previous wrap. At this time, the right end of the previous wrap forms the end of the wrap (the outer side of the overlap). The bonding interface of the polyethylene substrate corresponding to this end can serve as the above-mentioned extruded molten adhesive filling the overlapping transition position. Therefore, this part of the bonding interface can be called the extrusion slope. In the wrapping overlap direction (i.e., from left to right), the extrusion slope can be in an upward-lifting shape.

[0033] This upward - lifting form corresponds to the thickness of the polyethylene composite winding tape gradually decreasing from the mid - line of the tape width (i.e., at the 1 / 2 of the tape width) to the end. There are various ways to achieve the gradual thickness reduction. For example, the thickness can continuously decrease, such as in a circular arc shape or an oblique linear shape; the thickness can decrease step - by - step, and there can be one or more equal - thickness platforms with equal thickness. For example, there are a maximum - thickness equal - thickness platform and a minimum - thickness equal - thickness platform at the maximum - thickness position and the minimum - thickness position respectively. The maximum - thickness equal - thickness platform and the minimum - thickness equal - thickness platform are connected by a vertical line or an oblique line to form a stepped structure; or only a maximum - thickness equal - thickness platform is set, and then the thickness continuously decreases to the minimum thickness. For the convenience of processing, the lower surface of the polyethylene composite winding tape can be processed into a structure symmetric about the width mid - line.

[0034] The polyethylene composite winding tape can further assist in trimming the upper surface to further improve the quality of spiral winding. For example, trimming the edge at the overlapped and wound end can further promote the melting flow and exhaust of the adhesive. The cut angle is generally set at 5 - 30°, preferably 5 - 25°. Trimming the edge at the other end opposite to the overlapped and wound end can improve the overall flatness of the spiral winding layer, and the cut angle is generally set at 5 - 30°, preferably 5 - 25°.

[0035] The present invention can use existing polyethylene base materials and adhesive materials. Generally speaking, it only needs to meet the provisions of Standard GB / T 37587. The polyethylene sheet is extruded and rolled into the shape of the base material, and after the base material is irradiated, the adhesive layer is thermally compounded to form the polyethylene composite winding tape. The following will give examples of the specific implementation of the polyethylene composite winding tape of the present invention in combination with specific embodiments.

[0036] Example 1

[0037] In the embodiment of the polyethylene composite winding tape of the present invention, the structural schematic diagram is as Figure 1 shown, including a polyethylene base material 1 and an adhesive layer 2 compounded together up and down.

[0038] The upper surface of the polyethylene base material 1 is flat, thick in the middle and thin at both sides in the width direction. Specifically, the bonding interface between the polyethylene base material 1 and the adhesive layer 2 is in a circular - arc shape (with an arc radius R), and is divided into a left - hand bonding interface and a right - hand bonding interface along the width mid - line. The left - hand bonding interface and the right - hand bonding interface are symmetrically arranged on both sides of the width mid - line. Among them, the right - hand bonding interface corresponds to the overlapped and wound end, forming the above - mentioned extrusion end face 3. At this time, the width of the part with a decreasing height on one side of the polyethylene base material accounts for 50% of the total width of the base material.

[0039] In other implementation cases, such as Figure 2As shown, instead of using an arc transition from the width midline of the polyethylene substrate 1 to the left end and the right end, a diagonal transition connection is directly adopted. The combined part of the polyethylene substrate 1 and the adhesive layer 2 is in a triangular structure as a whole. At this time, the width of the part with a reduced height on one side of the polyethylene substrate accounts for 50% of the total width of the substrate.

[0040] As Figure 3 shown, the bonding interface between the polyethylene substrate 1 and the adhesive layer 2 is a stepped shape symmetrically arranged along the width midline. From the width midline to the right end, it includes a first stepped surface, a second stepped surface, and a third stepped surface connected in sequence. The first stepped surface has the largest thickness, the second stepped surface has the second largest thickness, and the third stepped surface has the smallest thickness. Taking the width of one side of the substrate as L / 2, the width range of the first stepped surface can be 0 - L / 4, and the thickness ranges of the second stepped surface and the third stepped surface can be 0 - L / 8. Figure 2 In this case, the number of steps of the step is 3. Of course, the number of steps of the step can also be 2, 4, or more. At this time, the width of the part with a reduced thickness on one side of the polyethylene substrate can account for more than 15% of the total width of the substrate, such as 15%, 20%, 30%, etc.

[0041] The left bonding interface can be symmetric or asymmetric with the right bonding interface. When it is asymmetrically arranged, it can present a shape that rises upward from right to left.

[0042] The right end of the polyethylene substrate is trimmed to form a first cut 4 at an angle of 5 - 30° with the horizontal direction, specifically, it can be 5°, 10°, 15°, 20°, 25°, 30°, etc. The left end is also trimmed to form a second cut 5 at an angle of 5 - 30° with the horizontal direction, specifically, it can be 5°, 10°, 15°, 20°, 25°, 30°, etc. The thickness of the remaining substrate after trimming can be 0.2 - 0.8 mm.

[0043] The lower surface of the adhesive layer 2 is flat, and the shape of the bonding interface of the adhesive layer 2 is complementary to the bonding interface of the polyethylene substrate 1.

[0044] The bandwidth L of the polyethylene composite winding tape can be 80 - 260 mm, the total thickness H can be 1.5 - 3.0 mm, the maximum thickness h1 of the polyethylene substrate can be 1.2 - 2.2 mm, and the maximum thickness h2 of the adhesive layer can be 0.5 - 1.4 mm. The typical thickness design can be carried out according to Table 1 below.

[0045] Table 1 Typical Thickness Design of Polyethylene Substrate (Unit: mm)

[0046]

[0047] II. Description of the Preferred Embodiment of the Pipeline Anti - corrosion Method of the Present Invention

[0048] Based on the above pipeline anti-corrosion method using polyethylene composite winding tape, it can be carried out according to the following steps:

[0049] (1) Apply a fusion-bonded epoxy powder primer on the surface of the bare pipe that has reached the specified effect before painting after surface pretreatment. This step can be carried out according to the regulations of the standard.

[0050] (2) Wind the above polyethylene composite winding tape on the fusion-bonded epoxy powder coating whose temperature is higher than the melting point of the adhesive layer, and then heat and fuse the wound polyethylene composite winding tape. When the polyethylene composite winding tape cools, the method of cooling with air first and then water is adopted. After the polyethylene composite winding tape is heated by infrared, the surface temperature reaches about 180 °C, and it is first cooled with compressed air to lower the surface temperature below 100 °C and then cooled and shaped with water.

[0051] The following is an example of the pipeline anti-corrosion method in combination with specific embodiments.

[0052] Example 2

[0053] The pipeline anti-corrosion method of this embodiment is specifically described as follows:

[0054] (1) Basic data

[0055] Anti-corrosion target: Natural gas transmission main line Steel hot-bent elbow, wall thickness 27, material X80;

[0056] Anti-corrosion structure: Fusion-bonded epoxy powder coating + polyethylene composite tape, 50% winding overlap;

[0057] Bottom layer thickness: Powder coating thickness ≥ 350 μm, total thickness ≥ 4 mm.

[0058] Anti-corrosion materials: Fusion-bonded epoxy powder: Powder coating temperature 210 °C - 230 °C; Polyethylene composite winding tape: Substrate arc + adhesive, winding bandwidth 120 mm, total thickness 2.40 mm (serial number 4 of the typical design thickness in Table 1).

[0059] (2) Process equipment

[0060] Elbow anti-corrosion production line: Medium-frequency heating system, powder spraying equipment, polyethylene tape automatic winding machine, infrared heating system, air-water cooling, elbow transmission line and tooling system.

[0061] (3) Execution and reference standards, quality requirements

[0062] Execution standard: GB / T 37587.

[0063] Reference standards: GB / T 23257, GB / T 39636.

[0064] Quality requirement: The effective cohesive peeling interface of the polyethylene composite tape > 90%.

[0065] (4) Anti-corrosion process flow

[0066] Rust removal effect before coating the elbow: The rust removal grade reaches Sa2.5, and the dustiness reaches grade 2;

[0067] Medium-frequency heating of the steel pipe: The elbow is heated by medium-frequency electric induction heating method and passes through the medium-frequency induction coil. The heating temperature of the elbow reaches the spraying temperature of the fusion-bonded epoxy powder, and the spraying temperature of the fusion-bonded epoxy powder is 210 - 230°C;

[0068] Powder spraying: Adopt a high-voltage electrostatic spraying system, and the thickness of the fusion-bonded epoxy powder coating ≥ 350μm;

[0069] Winding of the polyethylene composite tape: Wind the polyethylene composite winding tape on the groove of the winding machine. Before winding, the temperature of the fusion-bonded epoxy powder coating is not less than 190°C. Under the tension control mode, wind the polyethylene composite tape on the steel pipe with constant tension;

[0070] Infrared heating: The anti-corrosion layer of the polyethylene composite winding tape passes through the infrared heating coil, and the infrared heating temperature is 180°C.

[0071] (5) Implementation process

[0072] Transfer and tooling of the elbow: The bare elbow reaches the rust removal effect after shot blasting and rust removal. Place the elbow on the elbow transfer line and clamp it with the tooling fixture, and the elbow starts to be stably transferred.

[0073] Medium-frequency heating and powder spraying: The elbow is heated to 225°C after passing through the medium-frequency induction heating coil and undergoes high-voltage electrostatic spraying, and the thickness of the fusion-bonded epoxy powder spraying ≥ 350μm;

[0074] After the powder layer is initially cured, the surface temperature of the elbow drops to 190°C. At this time, the winding machine winds the polyethylene composite winding tape spirally on the elbow. The winding process is always wound in the constant tension control unwind mode. The polyethylene composite winding tape is closely attached to the bottom coating and heated under the action of tension. First, the adhesive layer starts to be heated and melted;

[0075] Infrared heating: After winding the polyethylene composite winding tape, the elbow enters the infrared heating coil, and the surface temperature of the heated polyethylene composite tape is 180°C.

[0076] Anticorrosion layer cooling: The polyethylene composite winding tape is first cooled with compressed air and then with water. The reason is that if the cooling water (room temperature 25±5°C) is directly sprayed onto the polyethylene composite winding tape anticorrosion layer above 100°C, it will rapidly cool and shrink, resulting in water shock marks and affecting the appearance. The current method is to first cool with compressed air to initially harden the surface of the anticorrosion layer, and then cool with water, achieving the appearance requirements of flat, bright, and spotless as specified in the anticorrosion layer process execution standard.

[0077] Effective bonding interface peel test: Conduct a peel test after the anticorrosion layer is cooled.

[0078] The peeling situation after winding with the polyethylene tape of CN118816030A is as Figure 4 shown, and the peeling situation after winding with the polyethylene tape of the present invention is as Figure 5 shown. From Figure 4 , Figure 5 it can be seen that after winding with the polyethylene composite winding tape of the present invention, the appearance is flat and there are no corrugations, which can further reduce the generation of drum hollows during winding overlap.

[0079] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polyethylene composite winding tape, comprising a polyethylene base material and an adhesive layer which are compounded up and down, characterized in that, The upper surface of the polyethylene base material is flat, and the lower surface decreases in height from the middle to both ends in the bandwidth direction; the lower surface of the adhesive layer is flat, and the upper surface is complementary in shape to the lower surface of the polyethylene base material; the lower surface part corresponding to the wound and overlapped end of the polyethylene base material forms an extrusion inclined surface, and the extrusion inclined surface extrudes the molten adhesive to flow and fill at the transition position between the lap and non-lap of the subsequent winding during winding and overlapping, compensating for the elevation difference at the transition position between the lap and non-lap.

2. The polyethylene composite winding tape according to claim 1, characterized in that, The extrusion inclined surface is an arc shape, an inclined linear shape or a stepped shape that rises upward along the winding and overlapping direction.

3. The polyethylene composite winding tape according to claim 2, wherein, The lower surface of the polyethylene base material is symmetric in shape along its width center line.

4. The polyethylene composite winding tape according to claim 1, wherein The maximum thickness of the polyethylene base material is 1.2 - 2.2 mm, and the maximum thickness of the adhesive layer is 0.5 - 1.4 mm; the total thickness of the polyethylene composite winding tape is 1.5 - 3.0 mm.

5. The polyethylene composite winding tape according to claim 1, wherein The upper surface of the wound and overlapped end of the polyethylene base material is trimmed to form a cut with an angle of 5 - 30° with the horizontal direction.

6. The polyethylene composite winding tape according to claim 4, characterized in that The upper surface of the other end of the polyethylene base material is trimmed to form a cut with an angle of 5 - 30° with the horizontal direction.

7. The polyethylene composite winding tape according to claim 5 or 6, characterized in that, The remaining thickness of the base material after trimming is 0.2 - 0.8 mm.

8. The polyethylene composite winding tape according to claim 1, characterized in that, The width of the part with a decreasing height on one side of the polyethylene base material accounts for 10 - 50% of the total width of the base material.

9. A pipeline anti-corrosion method, characterized in that, It includes the following steps: (1) Coat a fusion-bonded epoxy powder coating on the surface of the bare pipe whose surface pretreatment has achieved the specified effect before painting. (2) Wind the polyethylene composite winding tape according to any one of claims 1 - 8 on the fusion-bonded epoxy powder coating with a temperature higher than the melting point of the adhesive layer, and then heat and fuse the wound polyethylene composite winding tape. (3) After heating and fusing, the polyethylene composite winding tape is first cooled with compressed air and then cooled and shaped with water.

10. The pipeline anti-corrosion method according to claim 9, characterized in that, Cool with compressed air until the surface temperature is below 100°C, and then cool and shape with water.

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