CN114607844A - Steel wire reinforced thermoplastic plastic composite pipe for preventing end bulging failure and manufacturing method - Google Patents

Abstract

The invention relates to the field of thermoplastic composite pipes, and aims to provide a steel wire reinforced thermoplastic composite pipe and a manufacturing method for preventing end bulging failure. The composite pipe includes a thermoplastic inner layer, a steel wire reinforcement layer wrapped in hot melt adhesive, and a thermoplastic outer layer, and the adjacent structures are closely combined; It is formed by weaving, and has intersections formed by the intersection of steel wires with different winding directions; the intersections arranged along the circumferential direction at the outermost of the two ends of the composite pipe are fixedly connected by welding. The invention avoids the debonding of the steel-plastic interface and the pull-out of the steel wire which may occur in the service process of the composite pipe from the mechanism, and avoids the occurrence of bulging failure at the end. The invention does not need to perform flanging and other treatments on the composite pipe, and the technological process is simpler; the treated composite pipe has universality and can be applied to various existing joint connection modes.

Description

Steel wire reinforced thermoplastic composite pipe for preventing end bulging failure and manufacturing method

technical field

The invention relates to the field of thermoplastic composite pipes, in particular to a steel wire reinforced thermoplastic composite pipe for preventing end bulging failure and a manufacturing method.

Background technique

In recent years, with the development of economy, the demand for oil and gas resources is increasing day by day. Pipeline transportation, as a main transportation method carrying energy flow, has become an important link in the development and utilization of oil and gas resources due to its advantages such as one-time investment, low-cost operation, high safety, and suitability for long-distance transportation. In addition to oil and gas transportation, pressure pipelines are also widely used in urban water supply, heating, gas transmission, sewage and other fields. Pressure pipes include metal pipes, non-metal pipes, and composite pipes. The advantage of metal pipes is high strength, but metal pipes are easily corroded or even damaged by the environment and conveying medium during use. Non-metallic pipes are light in weight, strong in corrosion resistance, and quick to install. However, due to the characteristics of material structure, non-metallic pipes have disadvantages such as poor heat resistance and poor creep resistance. The composite pipe is made by combining the high strength of metal materials with the corrosion resistance of non-metallic materials. Reasonable selection of material types can make the composite pipe achieve the effect of complementing the advantages of mechanical properties and have better comprehensive performance.

Steel wire wound reinforced plastic composite pipe (plastic-steel-plastic composite pressure pipe, PSP pipe) is based on high-density polyethylene (HDPE) as the matrix, with a reticulated skeleton formed by high-strength steel wire as the reinforcement. It is bonded with high-strength steel wire by hot melt adhesive. With its unique structural advantages, PSP pipe has the advantages of high strength of steel pipe and corrosion resistance of plastic pipe at the same time, can withstand high working pressure and maintain certain toughness, and has been widely used in oil and gas fields, municipal construction, chemical industry, agriculture , thermal power generation and other fields.

The failure modes of PSP pipe mainly include strength failure, instability failure, leakage failure, and bulging failure at the joint end. The bulging of the joint end refers to the failure mode of bulging deformation and rupture at the pipe joint after the PSP pipe is loaded for a long time, and at the same time, the bulging deformation will be accompanied by the phenomenon of wire breakage. In engineering practice, the location where the end bulging failure occurs is usually the end or joint of the PSP pipe, and even if a metal reinforcing hoop is added to the bulging composite pipe, the pipe will still bulge at the joint. According to the actual engineering case, the higher the pressure load, the higher the temperature, and the longer the loading time, the higher the probability of end bulging failure of the PSP pipe. With the continuous expansion of the application range of PSP pipes, it is necessary to study how to avoid end bulging failure of PSP pipes during use.

The applicant's research team has carried out a lot of theoretical, experimental and simulation studies on the failure mode of PSP pipes in the previous research work. The main reason for the failure of end bulging is the debonding of the interface between steel wire and polyethylene, and a design and analysis method of PSP joint based on end bulging failure is proposed. The interface failure criterion and the influence of temperature and time on the interface strength are analyzed.

The study found that the process of bulging failure at the end of the PSP pipe is divided into two stages: the first stage occurs in the steel wire reinforcement layer of the PSP pipe, and the steel wire is subjected to shear stress along the direction of the steel wire, resulting in debonding between the steel wire and the plastic layer, causing Plastic interface failure. In the second stage, the debonding of the steel-plastic interface causes the stress redistribution at the steel wire, so that the unbonded steel wire reaches the strength limit in advance, causing the strength of the pipe to be damaged.

At present, in order to deal with the possible end bulging failure of the PSP pipe, the joint connection method is mainly used to improve the pressure bearing level of the connection part during the service process to ensure the long-term operation of the pipe. For example, in the Chinese patent application "A connection structure and connection method of a steel mesh skeleton polyethylene composite pipe" (CN201410450250.5), a certain length of PSP pipe is reserved for flanging, and a metal reinforcing ring is placed after flanging. The metal reinforcement ring is welded with the metal sleeve flare. This method avoids bulging of the end by improving the strength of the joint, but the processing and installation process of the pipe is complicated, additional tooling and pipe fittings are required, and the cost is high. On the basis of this joint connection method, various connection devices are designed to facilitate connection processing. For example, the Chinese patent application "A composite pipe riveting connection device" (CN201920997775.9) is provided with a "T"-shaped valgus at the outer end of the pipe. Structure, the pipe is riveted through the connector, and the steel wire reinforcement layer is riveted and deformed to avoid the risk of the connection end pulling out, but this patent only works on the steel wire reinforcement layer in the pipe joint, and the PSP pipe outside the joint There is still a risk of bulging failures. The existing method can achieve the effect of avoiding the bulging of the end of the pipe, but the effect is limited to the pipe inside the joint, which will cause the position where the bulging failure occurs to move to the outside of the joint; and the existing method needs to be flanged during the production process of the pipe, and the installation Corresponding connection devices make the pipe manufacturing process cumbersome, and the connection devices of different connection methods are different, so that the pipes of different connection devices cannot be universally used.

The technical idea proposed by the present invention to solve the bulging of the end is that by spot welding the intersection of the steel wire at the end of the pipe material, the force of the steel wire at the end of the composite pipe is transformed from the shear force between the steel wire and the resin to the interaction between the steel wire and the steel wire. Therefore, the phenomenon of debonding failure of the steel-plastic interface and the pull-off of the steel wire may occur at the end of the steel wire, and the purpose of preventing the bulging failure of the end of the steel wire is achieved. By proposing an end spot welding treatment method that can prevent the bulging failure of the end of the steel wire reinforced thermoplastic composite pipe, compared with the above-mentioned prior art, the method can change the stress mode of the steel wire at the end of the composite pipe, and reduce or reduce the load from the bearing mechanism. Shearing forces between wire and plastic are eliminated, thereby avoiding bulging failures. The method has convenient operation process, does not affect the original PSP pipe production process, and can be directly applied to the existing pipe production line.

SUMMARY OF THE INVENTION

The problem to be solved by the present invention is to overcome the deficiencies in the prior art and propose an end spot welding treatment method for preventing the end bulging failure of the steel wire reinforced thermoplastic composite pipe.

For solving the technical problem, the technical scheme adopted in the present invention is:

Provided is a steel wire reinforced thermoplastic composite pipe for preventing end bulging failure, comprising a thermoplastic inner layer, a steel wire reinforced layer wrapped in a hot melt adhesive, and a thermoplastic outer layer, and the adjacent structures are tightly combined; the The steel wire reinforcement layer has at least one layer, which is formed by a plurality of steel wires spirally intertwined and braided, and has an intersection formed by the intersection of steel wires with different winding directions; way to achieve a fixed connection.

As a preferred solution of the present invention, for the steel wire reinforcement layers of different layers, the fixed connection of the intersection is realized as follows:

(1) For the single-layer steel wire reinforcement layer: take the outermost circle intersection along the circumferential direction as the fixed connection point;

(2) For the double-layer steel wire reinforcement layer: the inner steel wire reinforcement layer is used as the benchmark, and the outer steel wire that intersects with each inner steel wire is selected according to the winding direction of the inner steel wire and the principle of the closest distance, and the most The outer intersection is used as a fixed connection point;

(3) For steel wire reinforcement layers with more than two layers: select one of the inner steel wire reinforcement layers as the benchmark, and select the outer steel wire that intersects with each inner steel wire according to the winding direction of the inner steel wire and the principle of the closest distance. The outermost intersection of the two serves as the fixed connection point.

As a preferred solution of the present invention, the material of the thermoplastic inner layer and the thermoplastic outer layer is any single resin in polyethylene, polypropylene or polyvinyl chloride, or modified by carbon black, carbon nanotubes or graphene. Any kind of composite resin.

As a preferred solution of the present invention, the steel wire reinforcement layer is a single-layer structure formed by forward and reverse interlaced weaving; The steel wires of the adjacent single-layer structure are in sufficient contact with each other.

As a preferred solution of the present invention, the melting point of the steel wire is in the range of 1400°C-1600°C, the diameter of the steel wire is in the range of 0.6mm-2.5mm, the carbon content in the steel wire material is less than 0.7%, and the surface of the steel wire is not coated to ensure that the steel wire is Direct contact is possible at the point of intersection.

The present invention further provides a method for preparing the aforementioned steel wire reinforced thermoplastic composite pipe, comprising the following steps:

(1) First extrude the inner layer of thermoplastic plastic, spray hot melt adhesive on its outer surface; then interlace the steel wire reinforcement layer on the outside of the hot melt adhesive, and then spray the hot melt adhesive to cover the steel wire reinforcement layer; finally extrude the thermoplastic plastic the outer layer to obtain a composite pipe;

(2) Cut both ends of the composite pipe according to the preset length, so that the end of the steel wire reinforcement layer exposes each steel wire end point for wiring during spot welding;

(3) Apply radial pressure to the two ends of the composite pipe, and ensure that the steel wires at the intersections arranged in the circumferential direction at the outermost of the two ends of the composite pipe keep close contact;

(4) Select the ends of two adjacent and intersecting steel wires in the steel wire reinforcement layer, connect them to the positive and negative poles of the electric welding machine power supply with wires respectively, and perform spot welding operations on the intersection of the steel wires by applying voltage; In the way of operating at the farthest intersection of the two ends of the composite pipe, alternate spot welding is performed on each intersection arranged in the circumferential direction to avoid local heat accumulation, and finally all the outermost intersections of the two ends of the composite pipe are fixedly connected.

As a preferred solution of the present invention, in the step (1), when the steel wire reinforcement layer has multiple layers, firstly spray hot melt glue on the outside of the innermost steel wire reinforcement layer to cover it, and then continue to interlace a layer of steel wire The reinforcement layer is then coated with hot melt adhesive; and so on, so as to realize the interval and coating of the multi-layer steel wire reinforcement layer by the hot melt adhesive.

As a preferred solution of the present invention, in the step (3), the radial pressure applied to the composite pipe does not exceed 1.2Mpa.

As a preferred solution of the present invention, in the step (4), the current reference value of the electric welding machine is maintained not less than 10A during the spot welding process, and the energization time of a single welding node is not more than 2s.

As a preferred solution of the present invention, in the step (4), the intersection point during spot welding and the steel wire to be connected are selected in the following manner:

(1) For the single-layer steel wire reinforcement layer: take the outermost intersection point along the circumferential direction as the fixed connection point, and connect the two wires to the power supply and the ends of the two steel wires forming the intersection point respectively;

(2) For the double-layer steel wire reinforcement layer: the inner steel wire reinforcement layer is used as the benchmark, and the outer steel wire that intersects with each inner steel wire is selected according to the winding direction of the inner steel wire and the principle of the closest distance, and the most The outer intersection is used as a fixed connection point; the two wires are respectively connected to the power supply and the ends of the inner and outer steel wires that form the intersection;

(3) For steel wire reinforcement layers with more than two layers: select one of the inner steel wire reinforcement layers as the benchmark, and select the outer steel wire that intersects with each inner steel wire according to the winding direction of the inner steel wire and the principle of the closest distance. The outermost intersection of the two is used as a fixed connection point; the two wires are respectively connected to the power supply and the ends of the inner and outer steel wires that form the intersection.

Description of the principle of the invention:

In the present invention, by means of spot welding performed by an electric welding machine, the steel wires wound in a positive and negative direction inside the composite pipe are fixedly connected at the intersection point closest to the end. Through the analysis of the end of the composite pipe, the original force of the two steel wires intersecting at one point is distributed along the respective winding directions of the two steel wires. distribution. Due to the change of the force distribution on the steel wire, for a single steel wire, the debonding of the steel-plastic interface and the pull-out of the steel wire during the bulging of the end of the composite pipe are avoided, and the possible failure mode is transformed into the strength of the steel wire or plastic material. destroy. When all the intersection points of the steel wires at the end of the composite pipe are connected by spot welding, the occurrence of end bulging failure can be avoided from the mechanism.

In the production process of the steel wire winding reinforced thermoplastic composite pipe, it has been ensured that each layer of steel wire reinforcement has sufficient contact. After the pipe production is completed, a radial pressure is applied to the end of the pipe, and a voltage is applied to the intersection of a pair of end steel wires. The current will form a path in the direction of least resistance, that is, starting from the intersection of a steel wire, passing through the intersection of two sections of steel wire in the direction of the steel wire, and then reaching the corresponding intersection point of the steel wire along the direction of the other steel wire. After the passage is formed, a current flows through the two sections of steel wire and their intersections. After the current flows through the resistance, heat will be released. In the passage, the intersection of the steel wires is the place where the resistance is the largest, and the intersection of the steel wires is the place where the heat release power is the largest. When the applied current is large enough, a large amount of heat is instantly generated at the intersection of the steel wires, so that the two sections of steel wire enter a molten state at the intersection point. Since the energization time is short enough, the spot welding process only generates heat at the intersection of the steel wire to complete the spot welding. After the voltage is removed, the heat dissipates along the wire with faster heat transfer and will not affect the plastic matrix near the intersection.

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

(1) The present invention performs spot welding connection processing on the intersection of the steel wires at the end of the composite pipe, which mechanically avoids the debonding of the steel-plastic interface and the pull-out of the steel wire that may occur during the service process of the composite pipe, thereby avoiding end bulging. failure occurs.

(2) The preparation method of the present invention does not require processing such as flanging of the composite pipe, and the technological process is simpler; the treated composite pipe is versatile and can be applied to various existing joint connection methods.

Description of drawings

FIG. 1 is a schematic diagram of the circuit connection of the spot welding treatment for the intersection of the steel wires at the end of the composite pipe according to the present invention.

Figure 2 is a schematic diagram of the end wire intersection point for a single-layer wire reinforcement layer.

FIG. 3 is a schematic diagram of the end intersection and the matching of the steel wires for the double-layer steel wire reinforcement layer.

FIG. 4 is a diagram showing the effect of analyzing the mechanical properties of the end of the composite pipe of the present invention before and after spot welding.

Detailed ways

The implementation of the present invention will be described in detail below.

The steel wire reinforced thermoplastic composite pipe for preventing end bulging failure of the present invention comprises a thermoplastic inner layer, a steel wire reinforced layer wrapped in a hot melt adhesive, and a thermoplastic outer layer, and the adjacent structures are tightly combined; The steel wire reinforcement layer has at least one layer, which is formed by a plurality of steel wires spirally interlaced and braided, and has a point of intersection formed by the intersection of steel wires with different winding directions; The intersection point is a fixed connection by welding.

For steel wire reinforced layers with different layers, the fixed connection of the intersection is realized as follows: (1) For single-layer steel wire reinforced layer: take the outermost intersection along the circumferential direction as the fixed connection point; (2) For double-layered steel wire reinforced layers The steel wire reinforcement layer: the steel wire reinforcement layer of the inner layer is used as the benchmark, and the outer steel wire that intersects with each inner steel wire is selected according to the winding direction of the inner steel wire and the principle of the closest distance, and the outermost intersection of the two is used as the fixed connection point. ; (3) For steel wire reinforcement layers with more than two layers: select one of the inner steel wire reinforcement layers as the benchmark, and select the outer steel wire that intersects with each inner steel wire according to the winding direction of the inner steel wire and the principle of the closest distance. Take the outermost intersection of the two as the fixed connection point.

The material of the thermoplastic inner layer and the thermoplastic outer layer can be any single resin of polyethylene, polypropylene or polyvinyl chloride, or any composite resin modified by carbon black, carbon nanotubes or graphene . The steel wire reinforcement layer can optionally be a single-layer structure formed by forward and reverse interlaced weaving; or a multi-layer structure formed by repeated stacking of multiple single-layer structures formed by forward and reverse interlaced weaving, and the steel wires of adjacent single-layer structures are mutually full contact. The melting point of the steel wire used is in the range of 1400℃-1600℃, the diameter of the steel wire is in the range of 0.6mm-2.5mm, the carbon content in the steel wire material is less than 0.7%, and the surface of the steel wire is not coated to ensure that the steel wire can be in direct contact at the intersection point.

The preparation method of the steel wire reinforced thermoplastic composite pipe of the present invention comprises the following steps:

(1) First extrude the inner layer of thermoplastic plastic, spray hot melt adhesive on its outer surface; then interlace the steel wire reinforcement layer on the outside of the hot melt adhesive, and then spray the hot melt adhesive to cover the steel wire reinforcement layer; finally extrude the thermoplastic plastic the outer layer to obtain a composite pipe;

When there are multiple layers of steel wire reinforcement, first spray hot melt adhesive on the outside of the innermost steel wire reinforcement layer to cover it, then continue to interlace a layer of steel wire reinforcement layer, and then cover it with hot melt adhesive; and so on. , so as to realize the interval and coating of the multi-layer steel wire reinforcement layer by the hot melt adhesive.

(2) Cut both ends of the composite pipe according to the preset length, so that the end of the steel wire reinforcement layer exposes each steel wire end point for wiring during spot welding;

(3) Apply a radial pressure of no more than 1.2MPa to the two ends of the composite pipe, and ensure that the steel wires at the intersections arranged in the circumferential direction at the outermost of the two ends of the composite pipe keep close contact; the specific radial pressure The value can be determined by referring to the "Handbook of Metals (Volume 6) Welding and Brazing".

(4) Select the ends of two adjacent and intersecting steel wires in the steel wire reinforcement layer, connect them to the positive and negative poles of the electric welding machine power supply with wires respectively, and perform spot welding operations on the intersections of the steel wires by applying a voltage; maintain during the spot welding process. The current reference value of the welding machine is not less than 10A, and the power-on time of a single welding node is not more than 2s. Under this current, the wire intersection has enough power to generate enough heat to ensure that the wire enters a molten state at the intersection, and at the same time, the energization time is controlled to be extremely short, so that the loop generates limited energy and is concentrated at the wire intersection with the greatest resistance, and excess energy It can be quickly transmitted along the steel wire to avoid the high temperature near the intersection of the steel wire and affect the performance of the plastic matrix. The welding current and energization time of the above spot welding are determined by referring to "Metal Handbook (Volume 6) Welding and Brazing".

In the process of spot welding operation, it is necessary to match the steel wire ends exposed by the corresponding steel wire reinforcement layers at the ends for the intersections of the steel wires to be connected by spot welding. By alternately selecting the opposite most distal intersections for operation, alternate spot welding is performed on the circumferentially arranged intersections to avoid local heat accumulation, and finally all the outermost intersections of the two ends of the composite pipe are fixedly connected. Specifically, select the intersection point and the wire to be connected during spot welding as follows:

(1) For the single-layer steel wire reinforcement layer: take the outermost intersection point along the circumferential direction as the fixed connection point, and connect the two wires to the power supply and the ends of the two steel wires forming the intersection point respectively;

(2) For the double-layer steel wire reinforcement layer: the inner steel wire reinforcement layer is used as the benchmark, and the outer steel wire that intersects with each inner steel wire is selected according to the winding direction of the inner steel wire and the principle of the closest distance, and the most The outer intersection is used as a fixed connection point; the two wires are respectively connected to the power supply and the ends of the inner and outer steel wires that form the intersection;

(3) For steel wire reinforcement layers with more than two layers: select one of the inner steel wire reinforcement layers as the benchmark, and select the outer steel wire that intersects with each inner steel wire according to the winding direction of the inner steel wire and the principle of the closest distance. The outermost intersection of the two is used as a fixed connection point; the two wires are respectively connected to the power supply and the ends of the inner and outer steel wires that form the intersection. During the welding process, the two matched steel wire terminals are energized to form a path, and the current in the path is maintained at a constant value and maintained for a certain period of time. The heat generated at the intersection causes the wires to melt, fuse, and cool to form a fixed connection.

In order to avoid the influence of heat accumulation during the welding process on the material properties of the composite pipe, during the welding process, the opposite most distal intersection points should be selected alternately, and the circumferentially arranged intersection points should be alternately spot welded. That is, for the intersection of the end of the same composite pipe, after completing one intersection welding, change the intersection at the farthest opposite end as the next welding position, and then replace it with another intersection at the farthest opposite end, and so on, until completion All intersections are welded. After the spot welding of all the intersections of the steel wires at the same end of the composite pipe is completed, the intersection of the steel wires at the other end shall be spot welded in the same order.

In conjunction with the accompanying drawings, a more detailed implementation process is described as follows:

As shown in Fig. 1, the present invention adopts the method of spot welding to connect the intersections of the steel wires at the ends of the steel wire wound reinforced thermoplastic composite pipe, including the composite pipe material that needs to be spot welded, the steel wire ends exposed at both ends of the pipe material, and the ends of the steel wires used for Welding machine that applies voltage to wire intersections to complete spot welding.

The composite pipe material that can be reinforced is a thermoplastic composite pipe with a thermoplastic inner layer, a steel wire reinforcement layer and a thermoplastic outer layer. The production process of the pipe can be briefly described as: extruding the plastic inner layer of the composite pipe, uniformly spraying the hot melt adhesive on the outside of the plastic inner layer, after spraying the hot melt adhesive, staggeredly wind the steel wire on the outer surface of the plastic inner layer, and then wind the steel wire. The hot melt adhesive is evenly sprayed on the steel wire reinforcement layer, and the plastic outer layer is extruded outside the steel wire reinforcement layer after spraying the hot melt adhesive. The pipe produced by this process ensures sufficient contact between the inner steel wire reinforcement layers.

The method of spot welding the end steel wire intersection point of the composite pipe is as follows:

(1) Put the pipe on the fixing device, and apply a radial pressure of no more than 1.2MPa to the end of the pipe.

(2) Determine the wire intersections that need to be spot welded, and match the wire intersections exposed at the ends of the two steel wires that form the wire intersections one by one.

(3) Spot welding is performed, and a large voltage is applied to the intersection of a pair of steel wires to maintain a path current of not less than 10A, and the power-on time is not more than 2s.

(4) After the spot welding is completed at the intersection of a pair of steel wires at the intersection of the steel wires, spot welding is performed on the intersection of the other steel wire with the farthest distance on the same end face, and this step is repeated until all the intersection points of the steel wires on the end face are spot welded.

(5) Reverse the direction of the pipe and spot weld the other end of the pipe.

As shown in Figure 2, all the steel wire intersections that need to be spot welded in the present invention are the intersections of a circle of steel wires in the steel wire reinforcement layer in the composite pipe that are closest to the end of the composite pipe. If the composite pipe has more than two steel wire reinforcement layers, it is necessary to All the intersections of the steel wires formed by each adjacent two layers of steel wires near the end of the pipe are connected by spot welding.

Taking the composite pipe with more than two steel wire reinforcement layers as an example, the method for selecting the intersection of steel wires in the present invention is:

(1) Determine the number of steel wire reinforcement layers in the composite pipe, and select two adjacent steel wire reinforcement layers to select the intersection point of the end steel wire.

(2) In the selected two-layer steel wire reinforcement layer, the inner steel wire reinforcement layer is selected as the benchmark, and a steel wire intersection point at which a voltage is applied at the end is determined in the inner steel wire reinforcement layer, and the winding direction of the inner steel wire reinforcement layer is determined. , along the winding direction of the inner layer steel wire to find the wire intersection point of the outer layer steel wire exposed at the end that is closest to the inner layer steel wire intersection point, and the outer layer steel wire intersection point is the end wire intersection point of the applied voltage that matches the inner layer steel wire intersection point. The above steps are repeated for the end steel wire intersections of each inner steel wire reinforcement layer in turn, so that each inner layer end steel wire intersection is matched with the outer layer end steel wire intersection.

(3) For a composite pipe with two steel wire reinforcement layers, the selection of the steel wire intersections on the end face has been completed; for a composite pipe with more than two steel wire reinforcement layers, the steel wire reinforcement layers need to be numbered from the inside to the outside. Select the adjacent steel wire reinforcement layers from the inside to the outside and repeat the step of selecting the intersection points of the end steel wires in (2) until all the intersection points of the end steel wires are selected.

(4) Reverse the direction of the composite pipe, and repeat the above process for the other end face until all the intersection points of the steel wires are selected.

As shown in Figure 3, when there are two inner and outer steel wire reinforcement layers, the schematic diagram of the matching effect of the steel wire contacts is shown in the figure. Each inner end wire intersection is matched with a corresponding outer end wire intersection.

The specific embodiments of the present invention are further described below in conjunction with specific examples:

In this example, a PSP pipe with model DN110 PN1.6 is used as an example, the thermoplastic is high-density polyethylene, and the number of steel wires is 32 for the inner layer and 20 for the outer layer. The end reinforcement of the composite pipe is carried out according to the following steps.

(1) According to the production requirements of PSP pipe, make or obtain the PSP pipe that meets the requirements, place the PSP pipe in the fixing device, and apply a radial pressure of 0.6MPa to a section of the pipe.

(2) Select the intersection point of the end steel wire, determine the winding direction of the inner steel wire reinforcement layer at one end, and number the wire intersection points 1-32 of the exposed steel wire at the end along the wire winding direction. For the intersection of No. 1 steel wire, look for the intersection of the outer layer of steel wire closest to the contact along the wire winding direction and mark it as 1', and then find the corresponding intersection of the outer layer of steel wire 1'-32' for all the intersections of the inner layer of steel wire of No. 1-32 in turn, The intersection points of the outer steel wires with different numbers can be the same point. Repeat the process for the wire intersection at the other end.

(3) Spot welding, connect the steel wire contact 1 and the steel wire contact 1' to the two poles of the spot welding power supply respectively, and adjust the output power of the welding machine, so that the output current of the welding machine is 200A, and the power-on time is 0.6s. After disconnecting the power supply and waiting for cooling, the spot welding of the steel wire contacts 1 and 1' is completed.

(4) On the same end face, perform the same spot welding process of connecting the power electrode, turning on the power and cutting off the power as in step (3) for the intersection of the wires farthest from the intersection of the wires and its corresponding intersection of the wires.

(5) Repeat the above steps (3) and (4) until all 32 pairs of steel wire intersections on the end face are spot welded.

(6) Reverse the direction of the composite pipe, and repeat steps (3) and (4) for the other end face of the composite pipe until all 64 pairs of steel wire intersections on the two end faces of the composite pipe complete the spot welding process.

The invention carries out the connection treatment of the steel wire intersection at the end of the steel wire winding reinforced thermoplastic composite pipe by spot welding, so that the composite pipe can avoid the possible debonding of the steel-plastic interface and the steel wire pulling away during the service process, and prevent the end of the composite pipe from the mechanism. Occurrence of external bulging failure. Figure 4 shows the results of the analysis of the mechanical properties of the end of the composite pipe before and after spot welding. The possible failure form before the spot welding connection is the failure of the steel-plastic interface. When the end interface stress reaches the interface shear strength, the steel-plastic interface fails. After the spot welding connection, the possible failure form at the end of the composite pipe is the material strength failure. The material fails when the compressive stress reaches the material strength; it can be seen from the figure that under the same service conditions, the theoretical bearing time of the composite pipe after spot welding is long.

Claims (10)

1. A steel wire reinforced thermoplastic plastic composite pipe for preventing end bulging failure comprises a thermoplastic plastic inner layer, a steel wire reinforced layer coated in hot melt adhesive, and a thermoplastic plastic outer layer, wherein adjacent structures are tightly combined; the steel wire reinforcing layer is provided with at least one layer, is formed by spirally winding and weaving a plurality of steel wires in a staggered way and has an intersection point formed by intersecting the steel wires in different winding directions; the composite pipe is characterized in that the intersection points which are positioned at the outermost sides of the two end parts of the composite pipe and are arranged along the circumferential direction are fixedly connected in a welding mode.

2. The steel wire reinforced thermoplastic composite pipe according to claim 1, wherein the fixed connection of the intersection points is achieved for different numbers of steel wire reinforced layers as follows:

(1) for a single steel wire reinforcement layer: taking a circle of intersection points at the outermost side along the circumferential direction as a fixed connection point;

(2) for a two-layer steel wire reinforcement layer: selecting an outer layer steel wire intersected with each inner layer steel wire according to the principle of the winding direction and the closest distance of the inner layer steel wires by taking the steel wire reinforcing layer of the inner layer as a reference, and taking the intersection point of the outermost sides of the inner layer steel wire and the outer layer steel wire as a fixed connection point;

(3) for steel wire reinforcement layers that exceed two layers: selecting one of the inner steel wire reinforcing layers as a reference, selecting the outer steel wire intersected with each inner steel wire according to the principle of the winding direction and the closest distance of the inner steel wires, and taking the intersection point of the outermost sides of the two steel wires as a fixed connection point.

3. The steel wire reinforced thermoplastic composite pipe according to claim 1, wherein the inner thermoplastic layer and the outer thermoplastic layer are made of a single resin selected from polyethylene, polypropylene, and polyvinyl chloride, or a composite resin modified with carbon black, carbon nanotubes, and graphene.

4. The steel-wire reinforced thermoplastic composite pipe as claimed in claim 1, wherein the steel-wire reinforced layer is a single-layered structure formed by forward and reverse alternate winding and weaving; or a multilayer structure formed by repeatedly nesting a plurality of single-layer structures formed by forward and reverse staggered winding and weaving, and the steel wires of the adjacent single-layer structures are fully contacted with each other.

5. The steel wire reinforced thermoplastic composite pipe according to claim 1, wherein the melting point of the steel wire ranges from 1400 ℃ to 1600 ℃, the diameter of the steel wire ranges from 0.6mm to 2.5mm, the carbon content in the steel wire material is less than 0.7%, and the surface of the steel wire is not coated to ensure that the steel wire can be directly contacted at the intersection point.

6. The method for preparing a steel wire reinforced thermoplastic composite pipe according to claim 1, comprising the steps of:

(1) firstly, extruding out an inner thermoplastic layer, and spraying hot melt adhesive on the outer surface of the inner thermoplastic layer; then, winding steel wire reinforcement layers on the outer sides of the hot melt adhesives in a staggered mode, and then spraying the hot melt adhesives to coat the steel wire reinforcement layers; finally, extruding the thermoplastic outer layer to obtain a composite pipe;

(2) cutting two ends of the composite pipe according to a preset length, and enabling the end part of the steel wire reinforcing layer to expose each steel wire end point for wiring during spot welding;

(3) applying radial pressure to the two end parts of the composite pipe and ensuring that steel wires at the outermost sides of the two end parts of the composite pipe at the intersection points arranged along the circumferential direction are kept in close contact;

(4) selecting two adjacent and intersected steel wire end parts in the steel wire reinforcing layer, respectively connecting the two adjacent and intersected steel wire end parts to the positive electrode and the negative electrode of a spot welding machine power supply through leads, and performing spot welding operation on the steel wire intersection points in a voltage applying mode; through the mode of selecting the most distal end nodical point of subtend by turns and operating, each nodical point of arranging in order to avoid local heat to gather in turn to each nodical point of circumference, make the fixed connection all of nodical point in two tip outsides of composite tube realize finally.

7. The method according to claim 6, wherein in step (1), when the steel wire reinforcement layers have multiple layers, firstly, hot melt adhesive is sprayed on the outer portion of the innermost steel wire reinforcement layer to coat the steel wire reinforcement layer, then, one steel wire reinforcement layer is continuously and alternately wound, and then, the steel wire reinforcement layer is coated with the hot melt adhesive; and the like, thereby realizing the spacing and the coating of the multilayer steel wire reinforcing layers by the hot melt adhesive.

8. The method of claim 6, wherein in step (3), the radial pressure applied to the composite tube does not exceed 1.2 MPa.

9. The method according to claim 6, wherein in the step (4), the current reference value of the spot welding machine is maintained to be not less than 10A during spot welding, and the power-on time of the single welding node is not more than 2 s.

10. The method according to claim 6, wherein in the step (4), the intersection points and the wires to be connected are selected at the spot welding in the following manner:

(1) for a single layer steel wire reinforcement layer: taking a circle of intersection points on the outermost side along the circumferential direction as fixed connection points, and respectively connecting two wires with a power supply and the end parts of two steel wires forming the intersection points;

(2) for a two-layer steel wire reinforcement layer: selecting an outer layer steel wire intersected with each inner layer steel wire according to the principle of the winding direction and the closest distance of the inner layer steel wires by taking the steel wire reinforcing layer of the inner layer as a reference, and taking the intersection point of the outermost sides of the inner layer steel wire and the outer layer steel wire as a fixed connection point; two wires are respectively connected with a power supply and the end parts of the inner layer steel wire and the outer layer steel wire which form the intersection point;

(3) for steel wire reinforcement layers that exceed two layers: selecting one of the inner steel wire reinforcing layers as a reference, selecting an outer steel wire intersected with each inner steel wire according to the principle of the winding direction and the closest distance of the inner steel wires, and taking the intersection point of the outermost sides of the two steel wires as a fixed connection point; two wires are respectively connected with the power supply and the end parts of the inner layer steel wire and the outer layer steel wire which form the intersection point.

Images