The difference between single-wall corrugated pipes and double-wall corrugated pipes

1. Construction technicians must carefully study the drawings, fully understand the design intent, promptly communicate any issues identified in the drawings with the owner, the supervisor, and the designers, conduct a drawing review meeting, and maintain detailed minutes of the meeting. Installation personnel must be familiar with the general properties of PE double-wall corrugated pipes and master the essential operational procedures. 2. Prior to commencing any prefabrication or fabrication work, prepare a materials schedule based on the design and construction drawings, procure the required materials and equipment according to specifications and models, and deliver them to the site. 3. Material and equipment requirements: Pipes, fittings, and other materials delivered to the site must undergo thorough inspection, with their material composition verified by the supervisor and the owner, and their certificates of conformity, specifications, and models confirmed. Only after passing inspection may they be stored in the warehouse, each item clearly labeled accordingly. 4. The inner and outer surfaces of pipes and fittings shall be smooth and even, free from bubbles, cracks, peeling, obvious surface marks, or depressions, and their color should be substantially uniform. 5. Pipe ends must be perpendicular to the pipe axis. Fittings must be complete, undamaged, and free from deformation. Proper preparation prior to the installation of PE double-wall corrugated pipes ensures construction quality and is a matter that every construction worker must take seriously.

What are the performance characteristics of polyethylene double-wall corrugated pipes?

Strong resistance to external pressure: The outer wall features an annular corrugated structure, which significantly enhances the pipe’s ring stiffness, thereby improving its ability to withstand soil loads. In this respect, polyethylene double-wall corrugated pipes offer a distinct advantage over other types of piping. Low construction costs: Under equivalent load conditions, polyethylene double-wall corrugated pipes can meet performance requirements with relatively thin walls. Consequently, compared with solid-wall pipes of the same material and specifications, they can save approximately half of the raw materials, resulting in lower overall construction costs—another notable feature of this pipe type. Convenient installation: Thanks to their light weight, polyethylene double-wall corrugated pipes are easy to handle and connect, enabling rapid installation and simplified maintenance. Their advantages become even more pronounced under tight project schedules or challenging construction conditions. Low friction and high flow capacity: Made from polyethylene, these pipes can convey greater flow rates than other pipes of the same nominal diameter. Alternatively, for a given flow requirement, a smaller‑diameter polyethylene double-wall corrugated pipe can be used. Excellent low-temperature resistance and impact strength: The embrittlement temperature of polyethylene double-wall corrugated pipes is −70°C. Under typical low-temperature conditions (above −30°C), no special protective measures are required during installation, making winter construction convenient. Moreover, these pipes exhibit excellent impact resistance.

Equipment for extrusion molding of polyvinyl chloride double-wall corrugated pipes

The extrusion equipment used for manufacturing double-wall corrugated PVC pipes is essentially similar to that used for single-wall corrugated pipes; the only difference lies in the die used to form the pipe parison. However, since double-wall corrugated pipes are typically produced in larger diameters and require greater quantities of raw material, it is advisable to employ a twin-screw extruder, which offers improved performance. Furthermore, the die structure for forming the parison of double-wall corrugated pipes differs from that of single-wall corrugated pipes in the following respects: the straight section of the die‑formed parison is longer; there are two melt‑diverting cones and two layers of melt flow channels, with the molten material in each channel forming the inner and outer walls of the double-wall pipe, respectively. Between these two melt flow channels, there is an additional compressed‑air inlet, through which compressed air is injected to inflate the outer wall, causing it to conform closely to the corrugated mold and thereby shaping the pipe’s corrugated profile. Additionally, the central bore of the inner mandrel can accommodate a heater and features passages for introducing compressed air and cooling water. On the other hand, the two die structures share certain similarities: both are equipped with a porous plate at the front of the melt‑diverting cone. Adjustments to the parison wall thickness are achieved by regulating the relative positions of the diverting cone and the mandrel, thereby controlling the gap between the mandrel and the die. Meanwhile, the die itself, being inserted between the two halves of the corrugation mold, remains fixed and cannot be moved.

Installation Method for Metal Expansion Joints

Comprehensive Guide to Metal Expansion Joint Installation: 1. Before installation, verify that the expansion joint’s model, specifications, and piping configuration comply with design requirements. 2. For expansion joints equipped with an inner sleeve, ensure the sleeve is oriented in the same direction as the fluid flow. For hinged expansion joints, the hinge rotation plane must align with the displacement‑rotation plane. 3. For expansion joints requiring “cold‑tightening,” any auxiliary components used for pre‑deformation should be removed only after the piping system has been fully installed. 4. It is strictly prohibited to adjust pipeline installation deviations by deforming the bellows of the expansion joint, as this can impair its normal operation, shorten its service life, and increase the loads on the piping system, equipment, and supporting structures. 5. During installation, avoid allowing welding spatter to come into contact with the bellows surface, and ensure the bellows is protected from other mechanical damage. 6. Once the piping system is installed, promptly remove the yellow positioning aids and fasteners used during transportation and installation, and adjust the limit devices to their specified positions as required by the design, ensuring the piping system maintains adequate compensation capacity under ambient conditions.

What are the standard performance characteristics of metal expansion joints?

Metallic compensators have two types of standard performance characteristics: one is the performance guaranteed for service, such as pressure resistance, temperature resistance, fatigue resistance, and elastic compensation; the other includes properties like stiffness and cross-sectional area, which are not directly required for operation but significantly influence piping system design and the application of metallic compensators. Therefore, it is essential to have a thorough understanding of both categories. Pressure-Resisting Capability of Compensators Compensators operate within pipelines and must withstand internal or external pressures. This necessitates that metallic compensators possess adequate pressure-resisting capacity. Through design and testing, appropriate structural parameters are established to ensure this capability. The pressure‑resisting capacity determined during design corresponds to the design pressure. Since compensators are produced in standardized series, they are categorized according to nominal diameter and nominal pressure. In most cases, their design pressures follow a series based on nominal pressures of 0.25, 0.6, 1.0, 2.5 MPa, and so forth. Only a small number of products are designed to meet specific pressure requirements outside these standard nominal pressure ranges. During piping system design, engineers determine the maximum operating pressure of the pipeline based on actual needs and then select a compensator with an appropriate nominal pressure rating. Compensation Capability of Compensators The compensation capability of a compensator arises from the elastic deformation of its bellows, which can involve axial extension, compression, bending, or combinations thereof. The magnitude of this compensation capability is specified by the designer according to operational requirements and is expressed as the rated compensation amount—indicating the maximum compensation achievable under given conditions. Different types of compensators exhibit distinct compensation modes, primarily including axial, lateral, angular, and combined compensation.

Compensator Classification and Characteristics

1. PTFE-lined bellows expansion joint: resistant to high temperatures, corrosion, and high pressure. This product employs a specially designed PTFE hose and a high‑temperature‑resistant braided stainless steel double‑clasp spiral hose, making it suitable for demanding environments involving high temperatures, corrosive media, and elevated pressures. 2. Bellows expansion joint: utilizes the effective axial and lateral deformation of its corrugated bellows to accommodate dimensional changes in pipelines, ducts, vessels, and other components caused by thermal expansion and contraction, or to compensate for axial, lateral, and angular displacements. It can also be used for noise reduction and vibration damping. 3. Metal flexible hose: compensates for axial and angular displacements in piping systems while providing pressure resistance, seismic protection, and noise reduction. 4. Rotary expansion joint: a displacement compensation device for district heating networks, primarily composed of inner and outer tubes, sealing packing, and a spring‑loaded compression mechanism. Its distinctive feature is the highly precise machining of the clearance between the spring‑loaded flange and the inner tube, ensuring minimal clearance. When two or three units are combined, they effectively absorb both axial displacement and axial thrust in district heating pipelines. 5. Spherical expansion joint: compensates for pipe deflection caused by foundation settlement or thermal expansion and contraction. It offers advantages such as large compensation capacity, compact installation footprint, low fluid resistance, ease of installation, and reduced overall cost. 6. Sleeve expansion joint: designed for straight‑run pipelines, suitable for hot water, steam, and oil‑based media. By allowing the inner sleeve to slide relative to the outer sleeve, it accommodates thermal expansion and provides compensation for thermal movement.

Structure and Types of Metal Bellows

The performance of a metal bellows depends on its structure; different structures exhibit distinct characteristics, which are reflected in the wave profile—defined as the pattern and shape of the corrugations when viewed in axial cross-section. Bellows typically feature U‑shaped, C‑shaped, Ω‑shaped, or S‑shaped waveforms. To enhance pressure‑bearing capacity and reduce stiffness, multi‑layer bellows and bellows equipped with reinforcing rings have been developed. In general, a circular cross‑section offers superior resistance to high pressures but permits only limited allowable displacement. By contrast, a U‑shaped cross‑section allows greater displacement at the expense of relatively lower pressure‑bearing capability. Under normal circumstances, the U‑shaped waveform is the most widely used domestically. When subjected to higher…

Application of Metal Bellows in Valves

Metal bellows are characterized by their ability to undergo corresponding displacements under the action of pressure, axial force, lateral force, or bending moment, and they also exhibit properties such as pressure resistance, vacuum tightness, corrosion resistance, thermal stability, and a long service life.