In industrial piping systems, there is a seemingly obscure but vital connecting element – the metal hose. It can not only bear pressure and temperature like steel pipe, but also bend and flex like rubber pipe, which makes it an indispensable flexible connection device in modern industry. From high-pressure pipelines in aerospace to the transport of corrosive media in petrochemicals, from vibration isolation of power equipment to pipeline connections for building firefighting, metal hoses play a key role in all walks of life thanks to their unique "rigid and soft" characteristics. This paper will systematically analyze the structural characteristics, selection parameters, installation specifications and maintenance points of metal hoses.
1. Structure and working principle of metal hose
Metal hose is a flexible connecting member consisting of corrugated flexible tube, mesh sleeve and joint. Its core structure is hierarchically distinct and each performs its own duties:
1. Corrugated flexible tube (inner tube)
Bellows are the core component of metal hoses and are made of thin-walled stainless steel (usually SUS304 or SUS316L) with a corrugated structure in the shape of a spiral or ring. This unique geometry gives it good flexibility – with low longitudinal and flexural stiffness, and the ability to work freely within the rated bending radius.
According to different corrugated shapes, metal hoses can be divided into:
- Ring-shaped bellows: good elasticity and small stiffness, suitable for occasions requiring large displacement compensation
- Spiral bellows: balanced stiffness and strength, suitable for high pressure conditions
2. Mesh sleeve (reinforcement layer)
The mesh sleeve is the "skeleton" of the metal hose, which is made of stainless steel wire or steel strip woven according to certain parameters and tightly wrapped around the outside of the bellows. Its roles include:
- Pressure-bearing enhancement: One, two or three layers of weave depending on hose caliber and pressure class
- Bellows Protection: Prevent the bellows from external mechanical damage
- Tensile support: Improve the tensile and torsional resistance of the hoisting hose
3. Connector (connector)
Fittings or flanges are arranged at both ends of the metal hose for connection with the piping system. There are various forms of joints, including external threaded joints, internal threaded joints, snap-type joints, flange connections, etc., which can be flexibly selected according to the on-site installation requirements.
2. Core performance characteristics of metal hoses
The reason why metal hoses are widely used in various industries is due to their excellent performances:
| Performance characteristics | Specific parameters/description |
|---|---|
| High and low temperature resistance | Operating temperature range-196℃ ~ +600℃ |
| Corrosion resistance | Chromium nickel austenitic stainless steel, suitable for corrosive media |
| Good flexibility | Can work smoothly within the rated bending radius |
| Anti-fatigue | The corrugated structure disperses stress and has strong capacity to bear alternating loads |
| Lightweight | Much lighter than rigid pipe under the same diameter |
| High pressure resistance | Braided mesh reinforcement, high-voltage models up to 6000 psig |
These characteristics make metal hoses used in many industries such as aerospace, petrochemical, metallurgy and power, construction and medicine, food and tobacco, etc.
III. Specifications and selection points of metal hoses
1. Specification Parameters
The specifications of metal hoses are usually expressed in diameter (DN), and the commonly used range is DN8-DN800mm. Take HANSA-FLEX KBO series products as an example:
| model | Inner diameter (mm) | Outer diameter (mm) | Operating pressure (bar) | Static bending radius (mm) |
|---|---|---|---|---|
| KBO 006 | 6.10 | 9.80 | 18.0 | 15 |
| KBO 016 | 16.20 | 21.60 | 5.0 | 28 |
| KBO 050 | 50.20 | 60.30 | 0.5 | 70 |
2. Key parameters of model selection
The correct choice of metal hoses requires consideration of the following factors:
| parameter | Key points of model selection |
|---|---|
| Diameter | Matches pipe caliber, DN8-DN800 |
| Connection form | Flanges, threads, sleeves, etc., selected according to site conditions |
| Working pressure | The design pressure should be greater than the system working pressure, but not too high (it will affect the bending ability) |
| Temperature correction | Temperature reduction of material permissible stress should be considered in high temperature operating conditions |
| Minimum bending radius | The flexure of the hose within this radius ensures normal life |
| Hose length | If it is too long, it will become unstable and increase flow resistance; Too short may result in inadequate compensation |
4. Selection and calculation formula of metal hose
The selection of metal hose length is the most error-prone link in the selection.
1. Axial displacement compensation
When there is axial thermal expansion in the pipeline, the length of the selected hose is calculated as follows:
L ≥ Lmin + x
Among them:
- L: Selected length of metal hose
- Lmin: straight length of hose after bending
- x: Axial compensation amount
2. Radial (lateral) displacement compensation
When there is a lateral displacement in the pipeline:
Y = L-lmin
Where:
- Y: radial compensation amount
- L: hose length
- Lmin: straight length of hose after bending
IMPORTANT: The metal hose itself cannot withstand axial tension and torsional deformation. If there is relative torsion or large radial offset at both ends during installation, the actual available compensation amount of the hose will be reduced, which may lead to fatigue damage and damage.
V. Installation Specifications and Precautions
1. Check before installation
- Check that the model, diameter and pressure grade of the metal hose are consistent with the design
- Check the bellows surface for mechanical damage and corrosion
- Verify that the joint threads are intact and the sealing surface is free of scratches
2. Key requirements during installation
According to industry experience, attention should be paid to when installing metal hoses:
| Precautions | Specific Description |
|---|---|
| Prevent welding splashes | Protective measures must be taken during welding, splashes will burn the bellows |
| Prohibition of mechanical injuries | Avoid the impact of heavy objects and scratches at acute angles of metal |
| No compulsory orthopedics | It is strictly prohibited to adjust the deviation of pipeline installation by deforming the hose |
| Avoid torsion | Do not allow both ends of the hose to twist relative to each other during installation |
| Reserve bend space | Ensure that the bending radius of the hose in the working condition is greater than the minimum value |
3. Inspection after installation
- Verify that the hose is not twisted or knotted
- Perform pressure test or airtightness test
- Check the connection for leaks
Operation maintenance and corrosion protection
1. Corrosion protection
The corrugated pipe of the metal hose is made of chromium nickel austenitic stainless steel, and special attention should be paid when using it:
- Prevent chloride dot corrosion: The water used for hydraulic test should control the chloride content
- Prevent acid corrosion: Avoid long-term contact with strong corrosive media such as dilute sulfuric acid and dilute hydrochloric acid
- Cleaning after pressure test: After the hydraulic test, the accumulated water should be drained in time to prevent rust and sediment deposition
2. Regular inspections
- Check the surface of the hose for cracks, corrosion marks and bulges
- Check the braided mesh sleeve for loose and broken threads
- Check the joint for looseness and leakage
3. Replacement cycle
The service life of metal hoses depends on working conditions and should be replaced when:
- There are obvious cracks or corrosion perforations on the bellows surface
- More than 10% of the total number of strands broken in the mesh jacket
- Serious corrosion of joints or seal failure
- Hose has been overpressurized or overheated
4. Overpressure protection
The tight pipe system shall strictly comply with the safe operating procedures to prevent hose pulling out or bursting due to overpressure caused by improper operation or other factors.
Implementation of Standards and Quality Assurance
The design, manufacture and inspection of metal hoses shall follow national standards. Currently valid criteria are:
- GB/T 14525-2010 General Technical Specification for Corrugated Metal Hoses
- Implementation date: 1 October 2011
- Central Unit: National Technical Committee for Standardization of Pipeline Accessories (TC237)
- Replacement standard: GB/T 14525-1993
This standard is applicable to corrugated metal hoses used in pipeline systems for compensating displacement and installation deviation, absorbing vibration and reducing noise, and covers all contents such as term definition, classification, requirements, inspection methods, inspection rules, signs and packaging, etc.
Revision Notice: At present, the standard is being revised, and the new standard No. 20256073-T-604 "General Technical Specification for Corrugated Metal Hoses" is in the drafting stage.
sum up
Metal hoses are indispensable flexible connection elements in modern industrial piping systems. Proper type selection, standard installation and regular maintenance are the three core elements to ensure its long-term reliable operation:
| Dimension | Core Essentials |
|---|---|
| Type selection | Select suitable materials and specifications according to diameter, pressure, temperature and corrosivity of media. The length must meet the requirements of compensation amount |
| install | Consistent flow direction marking, prevent welding splash, no torsional stretching, and reserve bending space |
| Criteria | Design and manufacture according to GB/T 14525-2010 national standard |
| antiseptic | Pay attention to chloride dot corrosion, and drain the accumulated water in time after hydraulic pressure test |
| lifetime | Check bellows, mesh sleeves and joints regularly, and replace them in time when they meet the replacement standards |
A metal hose with reasonable design and standard installation can run stably for a long time under harsh working conditions such as high temperature, high pressure and corrosion. It is suggested that the type selection calculation should be carried out according to GB/T 14525-2010 standard at the design stage, so as to ensure the safety and reliability of the pipeline system from the source.