Composite thermal insulation layer steam pipe and foaming forming process system of thermal insulation layer of composite thermal insulation layer steam pipe

Abstract

The invention discloses a steam pipe with a composite heat preservation layer. The steam pipe comprises a steam core pipe, an inorganic heat preservation layer, a polyurethane foaming layer and an outer sleeve from inside to outside. The polyurethane foaming layer between the inorganic thermal insulation layer and the outer sleeve is formed by annularly enclosing a plurality of polyurethane foaming bodies which are distributed in a circumferential array, and each polyurethane foaming body is in a strip shape extending in the axis direction of the steam core pipe; the periphery of each polyurethane foaming body is tightly surrounded by a circle of waist-ring-shaped elastic enclosing belt, and any two adjacent elastic enclosing belts are tightly attached to each other in the length direction, so that the plurality of polyurethane foaming bodies jointly form a polyurethane foaming layer; and the stability and thermal insulation performance of the foaming layer are effectively improved structurally and technologically.

Description

Technical Field

[0001] The invention belongs to the field of steam pipe insulation technology. Background Art

[0002] In the design and manufacture of high-temperature steam transmission pipelines with high thermal insulation performance requirements, the design of the insulation structure is particularly critical in order to minimize heat loss, maintain stable steam parameters, and ensure safe and efficient pipeline operation. In order to improve the thermal insulation performance, it is relatively basic to simply cover the inner core metal pipe with a layer of inorganic insulation (such as aluminum silicate fiber, rock wool, etc.). In order to pursue better thermal insulation effects, a metal sleeve is usually added to the outside of the inorganic insulation layer in engineering design, thereby forming an insulation structure from the inside to the outside, namely the inner core metal pipe, the annular inorganic insulation layer, and the outer protective pipe.

[0003] In order to fill the annular gap between the inner inorganic insulation layer and the outer protective tube and further improve the overall insulation performance, the process of injecting polyurethane foaming agent can be used to fill the space with closed-cell rigid foam polyurethane (PUR or PIR) formed by foaming, expanding and curing the liquid polyurethane material; this foam polyurethane becomes an effective supplementary insulation layer with its excellent low thermal conductivity.

[0004] However, the foaming cavity that needs to be filled is a circular cavity structure with a narrow ring-shaped cross-section and a long longitudinal extension. Such a geometric shape is not conducive to the infusion foaming process. The liquid mixture begins to enter this closed and narrow annular cavity to expand and foam. Since the material has viscosity changes and a certain fluidity during the foaming process, the material is prone to density differentiation effect in the annular cavity. Liquid components with relatively large density or materials that have not been fully foamed will tend to flow and gather to the "bottom" area of ​​the annular cavity due to gravity. Bubbles that are more fully foamed or have lower density may gather upward more quickly.

[0005] Relying solely on conventional infusion processes and the fluidity of the foaming agent itself, it is almost impossible to ensure the uniformity of polyurethane foam filling in this complex annular cavity structure; after the infusion operation is completed, it is very likely that large-volume voids or cavity areas will remain inside the solidified polyurethane foam insulation layer: the voids directly interrupt the thermal resistance path, greatly reducing the overall thermal insulation effect, causing a sharp increase in local heat loss in this area, and failing to meet the high insulation requirements of the design; secondly, the lack of foam support in the void area may cause heat to be transmitted outward through the metal path, forming a thermal bridge effect, causing the local temperature of the outer pipe surface to rise abnormally, bringing operational risks and even burn hazards; thirdly, uneven filling or voids may cause stress concentration, increasing the risk of structural damage during thermal expansion and contraction; this will also reduce the mechanical support and stability of the actual insulation layer, affecting the long-term safe operation of the pipeline system; therefore, how to effectively solve the problem of uniform polyurethane foam filling in the annular cavity is one of the key breakthroughs in improving the insulation technology of such pipelines. Summary of the Invention

[0006] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a composite insulation layer steam pipe and a foaming molding process system for its insulation layer, which effectively improves the stability and thermal insulation performance of the foaming layer both in structure and process.

[0007] Technical solution: To achieve the above purpose, the present invention provides a composite insulation layer steam pipe, which includes a steam core pipe, an inorganic insulation layer, a polyurethane foam layer and an outer sleeve from the inside to the outside.

[0008] The polyurethane foam layer between the inorganic thermal insulation layer and the outer sleeve is formed by a number of polyurethane foam bodies distributed in a circular array and enclosed in a ring shape. Each polyurethane foam body is in the shape of a strip extending along the axis of the steam core tube; the outer periphery of each polyurethane foam body is tightly surrounded by a circle of waist-shaped elastic enclosing belt, and any two adjacent elastic enclosing belts are tightly attached to each other along the length direction, so that the several polyurethane foam bodies together constitute a polyurethane foam layer.

[0009] Each polyurethane foam body is wrapped in a long strip cavity surrounded by the elastic enclosure belt, the outer wall of the inorganic thermal insulation layer and the inner wall of the outer sleeve, so that any two adjacent polyurethane foam bodies are independent of each other.

[0010] The inorganic thermal insulation layer is heat-resistant glass wool or aluminum silicate fiber; the polyurethane foam is hard polyurethane foam; and the elastic enclosure belt is silicone rubber.

[0011] Each elastic enclosure belt is formed by the expansion and deformation of a narrow closed-loop rubber belt; the two ends of the narrow closed-loop rubber belt are respectively put on the outside of the first push rod and the second push rod, and a narrow foamed polyurethane injection gap is formed on the inside of the narrow closed-loop rubber belt. After the foamed polyurethane is evenly injected into the narrow foamed polyurethane injection gap along the length direction, the narrow closed-loop rubber belt expands outward into an elastic enclosure belt under the rapid foaming and expansion of the foamed polyurethane on the inside.

[0012] A first annular clamp and a second annular clamp are coaxially mounted on the outer walls of the steam core tube at both ends of the inorganic thermal insulation layer; the outer ring of the first annular clamp is integrally provided with a plurality of first push rods radially arranged in a circular array, and the ends of the plurality of first push rods jointly support the inner wall of one end of the outer sleeve; the outer ring of the second annular clamp is integrally provided with a plurality of second push rods radially arranged in a circular array, and the ends of the plurality of second push rods jointly support the inner wall of the other end of the outer sleeve; thereby keeping the steam core tube and the outer sleeve coaxial.

[0013] The ends of the first push rod and the second push rod are spherical tops.

[0014] Insulation layer foaming molding process of composite insulation layer steam pipe:

[0015] Step 1: Install the steam core tube on the translation fixture;

[0016] Step 2: Coaxially wrap the inorganic insulation layer around the steam core tube;

[0017] Step 3: Coaxially and tightly install a first annular hoop and a second annular hoop on the outer walls of the steam core tube at both ends of the inorganic thermal insulation layer; by adjusting the circumferential positions of the first annular hoop and the second annular hoop, a plurality of first push rods outside the first annular hoop and a plurality of second push rods outside the second annular hoop correspond to each other;

[0018] Step 4: Prepare several narrow closed-loop rubber belts, and respectively put the two ends of each narrow closed-loop rubber belt over the corresponding first push rod and second push rod, so that a narrow foamed polyurethane injection gap is formed inside each narrow closed-loop rubber belt; at this time, the structure consisting of the steam core tube, the first annular hoop, the second annular hoop and the several narrow closed-loop rubber belts is recorded as a combined structure;

[0019] Step 5: Prepare an outer sleeve and fix it on a fixture that is coaxial with the steam core tube;

[0020] Step 6: Install a polyurethane foam injection device at one end of the outer sleeve close to the combined structure, the polyurethane foam injection device having a plurality of polyurethane foam spray guns;

[0021] Step 7: The displacement device drives one end of the combined structure to be inserted into one end of the outer sleeve along the axial direction and coaxially. At this time, the nozzle of each polyurethane foam spray gun is aimed at one end of a narrow and long polyurethane foam spraying gap;

[0022] Step eight, the nozzles of each polyurethane foaming spray gun simultaneously and continuously spray polyurethane foaming agent into the corresponding narrow and long foaming polyurethane injection gap, and at the same time, the displacement device drives the combined structure to quickly and completely insert into the outer sleeve along the axial direction within s, and immediately suspends the spraying; in the process of the above-mentioned combined structure being quickly and completely inserted into the outer sleeve, each narrow and long foaming polyurethane injection gap receives the polyurethane foaming agent uniformly along the length direction, and the narrow and long foaming polyurethane injection gap also quickly enters under the relative packaging of the inner wall of the outer sleeve and the outer wall of the inorganic thermal insulation layer The relatively closed state is achieved; the polyurethane foaming agent uniformly injected into the relatively closed narrow and long foamed polyurethane injection gaps along the length direction expands rapidly, so that the polyurethane foaming agent gradually foams and expands in the narrow and long foamed polyurethane injection gaps to uniformly and rapidly expand the narrow and long closed-loop rubber belt outward, and then the narrow and long closed-loop rubber belt expands outward into an elastic enclosing belt under the expansion action of the foamed polyurethane on the inside, until any two adjacent elastic enclosing belts are tightly attached to each other along the length direction, so that the polyurethane foam bodies in several elastic enclosing belts together constitute a polyurethane foam layer.

[0023] The process of installing a polyurethane foam injection device at one end of the outer sleeve close to the combined structure in "Step Six": The structure of the polyurethane foam injection device: includes an annular bracket, and the annular bracket is threaded in a circumferential array with three locking bolts extending in the radial direction. The annular bracket is put on the outside of one end of the outer sleeve, and then the three locking bolts are tightened so that the ends of each locking bolt are pressed against the outer wall surface of one end of the outer sleeve, so that the annular bracket is now coaxially clamped to the outside of the outer sleeve; one side of the annular bracket is fixedly connected to a plurality of polyurethane foam spray guns in a circumferential array through a plurality of spray gun arms, and the extension line of the nozzle of each polyurethane foam spray gun intersects with the axial direction of the outer sleeve at an angle; when working, the polyurethane foaming agent delivery pipe diverts the polyurethane foaming agent through the diversion pipe or diversion channel on the annular bracket to supply each polyurethane foaming spray gun.

[0024] Beneficial effects: This solution uses the diaphragm structure of the waist-ring-shaped elastic enclosure belt to make several polyurethane foam bodies independent of each other while maintaining their integrity. The elastic enclosure belt enclosed diaphragm structure can block the continuous circumferential heat transfer path along the polyurethane foam layer, reduce the thermal bridge effect caused by local defects, and thus reduce the overall heat loss; the independent insulation unit enclosed by several waist-ring-shaped elastic enclosure belts forms a local environment, avoiding the disorderly diffusion of heat in the insulation layer; and reducing the risk of cracking of the insulation layer due to stress concentration.

[0025] At the same time, the elastic enclosure belts in the waist ring form a physical barrier. If external moisture penetrates, it can limit the diffusion of moisture within a single partition, thereby preventing the entire insulation layer from becoming damp and failing. At the same time, the independent unit design can disperse external loads such as soil pressure and construction impact, reducing the risk of compression and deformation of the insulation layer. The local bearing capacity is further improved after zoning. At the same time, the diaphragm structure of the elastic enclosure belt in the waist ring blocks the extension path of cracks. Even if the local insulation layer cracks due to pipeline vibration, the damage is limited to a single zone, avoiding overall failure.

[0026] In the above process, since the polyurethane foaming agent is uniformly injected into each narrow and long polyurethane foam injection gap along the length direction, the problem of forming a large cavity during the one-time injection process of the existing annular cylindrical integrated polyurethane foam structure is avoided in principle. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the composite insulation layer steam pipe structure of this scheme;

[0028] Figure 2 This is a schematic diagram of the structure of the composite insulation layer steam pipe of this scheme with the outer sleeve partially hidden at one end;

[0029] Figure 3 This is a schematic diagram of the outer sleeve and the combined structure of this scheme being separated along the axis;

[0030] Figure 4 A schematic diagram of "step one" to "step three";

[0031] Figure 5 This is a schematic diagram at the end of "Step 4";

[0032] Figure 6 It is a schematic diagram of the structure of a narrow closed loop rubber belt;

[0033] Figure 7 This is the diagram at the end of "Step 5";

[0034] Figure 8 This is the diagram at the end of "Step 6";

[0035] Figure 9 This is the diagram at the end of "Step 7";

[0036] Figure 10 This is a schematic diagram at the end of "Step 8". DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings.

[0038] As attached Figures 1 to 10 A composite insulation layer steam pipe as shown, Figures 1 to 3As shown, it includes, from the inside to the outside, a steam core tube 1, an inorganic thermal insulation layer 2, a polyurethane foam layer and an outer sleeve 11; a first annular clamp 3a and a second annular clamp 3b are coaxially mounted on the outer wall of the steam core tube 1 at both ends of the inorganic thermal insulation layer 2; the outer ring of the first annular clamp 3a is integrally provided with a plurality of first push rods 4a arranged radially in a circumferential array, and the ends of the plurality of first push rods 4a jointly support the inner wall of one end of the outer sleeve 11; the outer ring of the second annular clamp 3b is integrally provided with a plurality of second push rods 4b arranged radially in a circumferential array, and the ends of the plurality of second push rods 4b jointly support the inner wall of the other end of the outer sleeve 11; thereby maintaining the steam core tube 1 and the outer sleeve 11 coaxially;

[0039] The inorganic thermal insulation layer 2 of this solution is heat-resistant glass wool or aluminum silicate fiber.

[0040] The composite insulation structure of this solution utilizes an "inorganic insulation layer 2 inside and a polyurethane foam layer outside" structural design. The core reason for this is that the operating temperature of high-temperature steam pipes often exceeds 200°C (even reaching 450°C), while the polyurethane foam layer has a temperature resistance limit of only approximately 120–140°C. Direct contact with the steam core pipe 1 will rapidly carbonize and fail. Therefore, the inner layer requires a high-temperature-resistant inorganic material (such as aluminum silicate, microporous calcium silicate, or glass wool, with a temperature resistance of 600–1000°C) to serve as a thermal barrier, reducing the interface temperature to a safe range for the organic layer. Simultaneously, the outer layer utilizes the polyurethane foam layer's ultra-low thermal conductivity (0.016–0.024 W / m·K) and closed-cell waterproof properties (high moisture resistance factor) to effectively isolate soil moisture intrusion and reduce overall heat loss. Furthermore, this structure reduces thermal stress through the inner layer's inorganic material's low thermal expansion coefficient (close to that of steel pipes). The outer layer's flexibility and rigid support (combined with the steel casing) jointly ensure the pipe's freedom from thermal displacement and stability against soil pressure.

[0041] like Figure 2 and 3 As shown, the above structure is further optimized. The polyurethane foam layer between the inorganic insulation layer 2 and the outer sleeve 11 of this solution is formed by a plurality of polyurethane foam bodies 15 distributed in a circumferential array and surrounded in an annular shape. The polyurethane foam body 15 is a hard polyurethane foam (density 60-80kg / m 3 , thermal conductivity 0.013–0.03kcal / m·h·℃, closed porosity > 92%, water absorption ≤ 0.2kg / m 2Each polyurethane foam body 15 is in the shape of a strip extending along the axis of the steam core tube 1; the outer periphery of each polyurethane foam body 15 is tightly surrounded by a circle of waist-shaped elastic enclosure belt 5a, and any two adjacent elastic enclosure belts 5a are tightly attached to each other along the length direction, so that several polyurethane foam bodies 15 together constitute a polyurethane foam layer; each polyurethane foam body 15 is wrapped in a long strip cavity surrounded by the elastic enclosure belt 5a, the outer wall surface of the inorganic thermal insulation layer 2, and the inner wall surface of the outer sleeve 11, so that any two adjacent polyurethane foam bodies 15 are independent of each other; Each elastic enclosure belt 5a of the present scheme is formed by the expansion deformation of a narrow closed-loop rubber belt 5, and the material of the narrow closed-loop rubber belt 5 is elastic and soft silicone rubber material; the two ends of the narrow closed-loop rubber belt 5 are respectively sleeved on the outside of the first push rod 4a and the second push rod 4b, and a narrow foamed polyurethane injection gap 6 is formed on the inside of the narrow closed-loop rubber belt 5. After the foamed polyurethane is uniformly injected into the narrow foamed polyurethane injection gap 6 along the length direction, the narrow closed-loop rubber belt 5 expands outward into an elastic enclosure belt 5a under the rapid foaming and expansion action of the foamed polyurethane on the inside.

[0042] For smoother coaxial assembly, the ends of the first push rod 4a and the second push rod 4b are spherical.

[0043] The diaphragm structure formed by the waist-ring-shaped elastic enclosure belt 5a enables the multiple polyurethane foam bodies 15 to be independent of each other while maintaining their integrity. The enclosed diaphragm structure of the elastic enclosure belt 5a can block the continuous circumferential heat transfer path along the polyurethane foam layer, reducing the thermal bridge effect caused by local defects such as cavities and cracks, thereby reducing overall heat loss; the independent insulation unit enclosed by the multiple waist-ring-shaped elastic enclosure belts 5a forms a local environment to prevent disorderly diffusion of heat in the insulation layer; the thermal conductivity coefficient of polyurethane is as low as 0.022-0.025W / (m·K), and the partition design can further reduce heat loss by more than 10%; at the same time, high-temperature steam pipes (above 200°C) expand and contract significantly due to heat and cold, and the partition design allows each unit to expand and contract independently, reducing the risk of cracking of the insulation layer due to stress concentration.

[0044] Each elastic waist-shaped band 5a forms a physical barrier. If external moisture intrudes, it limits its diffusion to a single zone, preventing the entire insulation layer from failing due to moisture. While the polyurethane has a closed-pore ratio of >95%, moisture intrusion can still increase its thermal conductivity; this design delays this process. Furthermore, the independent unit design distributes external loads such as soil pressure and construction impact, reducing the risk of compression deformation within the insulation layer. The polyurethane has a compressive strength of 120–220 MPa, further enhancing its localized pressure-bearing capacity through zoning. Furthermore, the membrane structure of the elastic waist-shaped band 5a blocks crack propagation paths. Even if the insulation layer cracks locally, such as due to pipeline vibration, the damage is limited to a single zone, preventing overall failure.

[0045] This insulation pipe has advantages not only in its own structure, but also in its process advantages. It can effectively solve the existing problem of being unable to ensure the uniformity of polyurethane foam filling in this complex annular cavity structure; after the pouring operation is completed, it is very likely that large-volume cavities or void areas will remain inside the solidified polyurethane foam insulation layer. The specific process is as follows:

[0046] The foaming molding process system of the composite insulation layer steam pipe includes the following steps:

[0047] like Figure 4 As shown, in step 1, the steam core tube 1 is mounted on a translation fixture. In order to facilitate subsequent steps such as wrapping, the steam core tube 1 is clamped by the translation fixture on the inner wall of the steam core tube 1, such as by an internal support chuck clamping;

[0048] Step 2: Coaxially wrap the inorganic insulation layer 2 around the steam core tube 1;

[0049] Step 3: Install the first annular hoop 3a and the second annular hoop 3b coaxially and tightly on the outer wall of the steam core tube 1 at both ends of the inorganic thermal insulation layer 2; the outer rings of the first annular hoop 3a and the second annular hoop 3b are respectively integrally provided with a plurality of first push rods 4a and a plurality of second push rods 4b radially arranged in a circumferential array;

[0050] By adjusting the circumferential positions of the first annular hoop 3a and the second annular hoop 3b, the first push rods 4a outside the first annular hoop 3a correspond to the second push rods 4b outside the second annular hoop 3b. The one-to-one correspondence here means that the corresponding first push rods 4a and second push rods 4b overlap in the axial direction of the steam core tube 1.

[0051] Step 4: Figure 5 As shown, a plurality of narrow closed-loop rubber belts 5 are prepared, and the two ends of each narrow closed-loop rubber belt 5 are respectively put on the outside of the corresponding first push rod 4a and second push rod 4b, so that a narrow foamed polyurethane injection gap 6 is formed inside each narrow closed-loop rubber belt 5. At this time, the structure composed of the steam core tube 1, the first annular hoop 3a, the second annular hoop 3b and the plurality of narrow closed-loop rubber belts 5 is recorded as a combined structure 8.

[0052] Step five, such as Figure 7 As shown, prepare an outer sleeve 11 and fix the outer sleeve 11 on a fixture coaxial with the steam core pipe 1;

[0053] Step six, such as Figure 8As shown, a polyurethane foam injection device 9 is installed at one end of the outer sleeve 11 close to the combined structure 8. The structure of the polyurethane foam injection device 9 is as follows: it includes an annular bracket 17, and the annular bracket 17 is threaded with three locking bolts 16 extending in the radial direction in a circumferential array. The annular bracket 17 is sleeved on the outside of one end of the outer sleeve 11, and then the three locking bolts 16 are tightened so that the ends of the locking bolts 16 are pressed against the outer wall surface of one end of the outer sleeve 11, so that the annular bracket 17 is now coaxially embraced outside the outer sleeve 11; one side of the annular bracket 17 is fixedly connected to a plurality of polyurethane foam spray guns 12 in a circumferential array through a plurality of spray gun arms 14, and the extension line of the nozzle 13 of each polyurethane foam spray gun 12 intersects with the axial direction of the outer sleeve 11 at an angle; the polyurethane foaming agent delivery pipe 18 supplies the polyurethane foaming agent to each polyurethane foaming spray gun 12 through a diversion pipe or diversion channel on the annular bracket 17;

[0054] Step seven, such as Figure 9 As shown, the displacement device drives one end of the combined structure 8 to be inserted into one end of the outer sleeve 11 along the axial direction coaxially. At this time, the nozzle 13 of each polyurethane foam spray gun 12 is aimed at one end of a narrow and long polyurethane foam spraying gap 6;

[0055] Step eight, such as Figure 10 As shown, the nozzles 13 of the polyurethane foaming spray guns 12 simultaneously and continuously spray the polyurethane foaming agent into the corresponding elongated polyurethane foaming injection gaps 6. At the same time, the displacement device drives the combined structure 8 to quickly and completely insert into the outer sleeve 11 within 5 seconds along the axial direction, and immediately suspends the spraying. During the process of the above-mentioned combined structure 8 being quickly and completely inserted into the outer sleeve 11, each elongated polyurethane foaming injection gap 6 receives the polyurethane foaming agent uniformly along the length direction. At the same time, the elongated polyurethane foaming injection gaps 6 also quickly enter a relatively closed state under the relative packaging of the inner wall of the outer sleeve 11 and the outer wall of the inorganic thermal insulation layer 2. ; The polyurethane foaming agent uniformly injected along the length direction into the relatively closed narrow and long foamed polyurethane injection gaps 6 expands rapidly, so that the polyurethane foaming agent gradually foamed and expanded in the narrow and long foamed polyurethane injection gaps 6 stretches the narrow and long closed-loop rubber belt 5 outward uniformly and rapidly, and then the narrow and long closed-loop rubber belt 5 expands outward into an elastic enclosure belt 5a under the expansion action of the foamed polyurethane on the inside, until any two adjacent elastic enclosure belts 5a are tightly attached to each other along the length direction, so that the polyurethane foam bodies 15 in several elastic enclosure belts 5a together constitute a polyurethane foam layer; at this point, the uniform filling process of the polyurethane foam layer is completed.

[0056] In the above process, since the polyurethane foaming agent is uniformly injected into each narrow and long polyurethane foam injection gap 6 along the length direction, the problem of forming a large cavity during the one-time injection process of the existing annular cylindrical integrated polyurethane foam structure is avoided in principle.

[0057] The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A composite insulation layer steam pipe, characterized by: It comprises a steam core tube (1), an inorganic heat-insulating layer (2), a polyurethane foaming layer and an outer sleeve (11) from the inside to the outside; The polyurethane foam layer between the inorganic thermal insulation layer (2) and the outer sleeve (11) is formed by a plurality of polyurethane foam bodies (15) distributed in a circumferential array and enclosed in an annular shape, wherein each polyurethane foam body (15) is in the shape of a strip extending along the axial direction of the steam core tube (1); the outer periphery of each polyurethane foam body (15) is tightly surrounded by a waist-ring-shaped elastic enclosing belt (5a), and any two adjacent elastic enclosing belts (5a) are closely attached to each other along the length direction, so that the plurality of polyurethane foam bodies (15) together constitute the polyurethane foam layer; Each polyurethane foam body (15) is wrapped in a long strip cavity surrounded by the elastic enclosure belt (5a), the outer wall of the inorganic thermal insulation layer (2), and the inner wall of the outer sleeve (11), so that any two adjacent polyurethane foam bodies (15) are independent of each other.

2. The composite insulation layer steam pipe according to claim 1, characterized in that: The inorganic heat-insulating layer (2) is heat-resistant glass wool or aluminum silicate fiber; the polyurethane foam (15) is hard polyurethane foam; and the elastic enclosing belt (5a) is silicone rubber.

3. The composite insulation layer steam pipe according to claim 2, characterized in that: Each elastic enclosure belt (5a) is formed by the expansion deformation of a narrow closed-loop rubber belt (5); the two ends of the narrow closed-loop rubber belt (5) are respectively sleeved outside the first push rod (4a) and the second push rod (4b), and a narrow foamed polyurethane injection gap (6) is formed inside the narrow closed-loop rubber belt (5). After the foamed polyurethane is uniformly injected into the narrow foamed polyurethane injection gap (6) along the length direction, the narrow closed-loop rubber belt (5) expands outwards to form the elastic enclosure belt (5a) under the rapid foaming and expansion action of the foamed polyurethane inside.

4. The composite insulation layer steam pipe according to claim 3, characterized in that: A first annular hoop (3a) and a second annular hoop (3b) are coaxially mounted on the outer walls of the steam core tube (1) at both ends of the inorganic thermal insulation layer (2); the outer ring of the first annular hoop (3a) is integrally provided with a plurality of first push rods (4a) arranged radially in a circumferential array, and the ends of the plurality of first push rods (4a) jointly support the inner wall of one end of the outer sleeve (11); the outer ring of the second annular hoop (3b) is integrally provided with a plurality of second push rods (4b) arranged radially in a circumferential array, and the ends of the plurality of second push rods (4b) jointly support the inner wall of the other end of the outer sleeve (11); thereby, the steam core tube (1) and the outer sleeve (11) are kept coaxial.

5. The composite insulation layer steam pipe according to claim 4, characterized in that: The ends of each first push rod (4a) and second push rod (4b) are spherical tops.

6. The foaming molding process for the thermal insulation layer of a composite thermal insulation layer steam pipe according to claim 4, characterized in that: Step 1: Install the steam core tube (1) on a translation fixture; Step 2: Coaxially sleeve the inorganic thermal insulation layer (2) on the outside of the steam core tube (1); Step 3: Coaxially and tightly install a first annular hoop (3a) and a second annular hoop (3b) on the outer wall of the steam core tube (1) at both ends of the inorganic thermal insulation layer (2); By adjusting the circumferential position of the first annular hoop (3a) and the second annular hoop (3b), a plurality of first push rods (4a) outside the first annular hoop (3a) and a plurality of second push rods (4b) outside the second annular hoop (3b) are made to correspond one to one; Step 4: prepare a plurality of narrow closed-loop rubber belts (5), and respectively put the two ends of each narrow closed-loop rubber belt (5) on the outside of the corresponding first push rod (4a) and the second push rod (4b), and form a narrow foamed polyurethane injection gap (6) inside each narrow closed-loop rubber belt (5); at this time, the structure composed of the steam core tube (1), the first annular hoop (3a), the second annular hoop (3b) and the plurality of narrow closed-loop rubber belts (5) is recorded as a combined structure (8); Step 5: prepare an outer sleeve (11) and fix the outer sleeve (11) on a fixture that is coaxial with the steam core tube (1); Step 6: Install a polyurethane foam injection device (9) at one end of the outer sleeve (11) close to the combined structure (8), and the polyurethane foam injection device (9) has a plurality of polyurethane foam spray guns (12); Step 7: The displacement device drives one end of the combined structure (8) to be coaxially inserted into one end of the outer sleeve (11) along the axial direction. At this time, the nozzle (13) of each polyurethane foam spray gun (12) is aligned with one end of a narrow and long polyurethane foam spraying gap (6); Step eight, the nozzles (13) of each polyurethane foaming spray gun (12) simultaneously and continuously spray the polyurethane foaming agent into the corresponding narrow and long polyurethane foaming injection gap (6), and at the same time, the displacement device drives the combined structure (8) to quickly and completely insert into the outer sleeve (11) within 5 seconds along the axial direction, and immediately suspends the spraying; in the process of the above-mentioned combined structure (8) quickly and completely inserting into the outer sleeve (11), each narrow and long polyurethane foaming injection gap (6) receives the polyurethane foaming agent uniformly along the length direction, and the narrow and long polyurethane foaming injection gap (6) is also relatively encapsulated between the inner wall of the outer sleeve (11) and the outer wall of the inorganic thermal insulation layer (2). The narrow closed-loop rubber band (5) is rapidly expanded outwards by the gradually expanded polyurethane foaming agent in the narrow closed-loop rubber band (5), and the narrow closed-loop rubber band (5) is expanded outwards into an elastic enclosure band (5a) under the expansion effect of the foaming polyurethane on the inside, until any two adjacent elastic enclosure bands (5a) are closely attached to each other along the length direction, so that the polyurethane foam bodies (15) in the plurality of elastic enclosure bands (5a) together constitute a polyurethane foam layer.

7. The foaming molding process for the thermal insulation layer of a composite thermal insulation layer steam pipe according to claim 6, characterized in that: In "step six", the polyurethane foam injection device (9) is installed at one end of the outer sleeve (11) close to the combined structure (8): the polyurethane foam injection device (9) includes an annular bracket (17), and the annular bracket (17) is threaded with three locking bolts (16) extending in the radial direction in a circumferential array. The annular bracket (17) is sleeved on the outside of one end of the outer sleeve (11), and then the three locking bolts (16) are tightened so that the ends of the locking bolts (16) are pressed against the outer wall of one end of the outer sleeve (11), so that the annular bracket (17) is coaxially held outside the outer sleeve (11); one side of the annular bracket (17) is fixedly connected to a plurality of polyurethane foam spray guns (12) in a circumferential array through a plurality of spray gun arms (14).

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