Metal hoses - it is the connecting flexible elements of pipelines, which are designed for transportation of liquid or gas media under high or low pressure, while ensuring the tightness of the circuit in a wide temperature range,
The main element providing hose flexibility is its corrugated part that is made of corrosion-resistant high-alloy steel. Metal braid reinforces the construction that allows to use the hose at the highest pressure. Corrugated shell is made by winding on top of the corrugation with a profiled band. The corrugations may be spiral or circular. Sleeves with helical (spiral) arrangement of the corrugations may be reinforced by a wire spiral in diameter. Ring-shaped corrugations are more common because they are not subject to torsion under high pressure during longitudinal tension. The main strength element of metal hose is the braid, which is used to protect the hose from unexpected damage. Braid under the influence of radial and axial loads, including the pulsation of pressure during transportation of fluids or gases through the system, should ensure the operation of the hose.
Metal hoses are produced in one or more braids, the number of which depends on the values of working pressure. The braid provides performance under the influence of radial and axial loads and pressure pulsations, which are inevitable when moving liquid or gas media in the pipeline. Such braiding is usually of mesh type made of stainless wire 12X18H9T with section of 0.3; 0.4; 0.5; 0.6 mm. To connect to the main circuit is a fitting on the end of the sleeve. Fittings are connected to the flexible part of the hose by soldering with acid-resistant solder or by welding (by argon-arc or contact roller). A cup is put on the braid on the end corrugations at the place of fitting attachment, which protects the corrugations from thermal effects of welding and soldering. If necessary, it is allowed by agreement with the customer to weld special connecting fittings, which are designed according to the customer's drawings. Internal and external surfaces of metal hoses shall be free of gross mechanical damage, visible dirt and other defects which are not stipulated by the material specification. The braid shall fit tightly around the hose and shall not have any torn strands and wires protruding outward.
Metal hoses are made with different internal nominal diameters of corrugated sealed shell to values of DN 300 mm. The size of the connecting fittings for welding in the form of rings is mounted on the basis of the requirements for the working pressure for the hose. In order to comply with TS requirements - length of flexible free part of metal hose shall be not less than 250 mm. As agreed with customer it shall be possible to produce hoses in assembly by joining of several hoses. Such joining shall be performed by welding using welding rings.
Metal hoses are designed for transportation of media at t ° up to 400 ° C. When ordering hoses must specify the transported medium, operating temperature range and other parameters. Working pressure (P oper.) - pressure of the transported medium, in daily operation. Pressure rating (PN) - the highest working pressure at which the hose is allowed to operate under normal operating conditions. Due to reliability and long service life flexible metal hoses are widely used: in machine engineering, aircraft, shipbuilding, in industrial chemistry, metallurgy, heat power engineering, for creation of cryogenic equipment.
Absorption of vibrations during transportation of liquids or gases at different temperatures and pressures; providing protection against accidental damage; providing reliable connections to moving equipment of the pipeline; elimination of inaccuracies during installation of the circuit. Strength of metal hoses are determined by the number of braids, which serve as reinforcement, the profile of the corrugated part: the parameters of the corrugation, the number of corrugations per unit length, wall thickness and material, which affects the resistance to the media and conditions of mechanical, chemical and thermal effects. Corrosion resistance depends on the resistance of stainless steel 12Х18Н10Т in the braid and the resistance of the flexible element. Particularly harmful is pitting corrosion caused by chlorine-containing media and contact with sea water.
Longevity of metal hoses is directly dependent on the number of load cycles - one load cycle - one movement of the hose and return it to its original position. Other factors are: pressure and temperature, the amplitude of their fluctuations, the frequency of movement of the hose, the minimum bending radius, the aggressive effects of the working environment, vibration. In fuel and hydraulic systems the hoses are subjected to fluid pressure of pulsating character, which can cause destruction of flexible piping, at pressures, an order of magnitude smaller than static loads. The source of pulsation is plunger and gear pumps. Sudden sudden closing of valves causes hydrodynamic shock, which also leads to shell failure. To increase reliability it is necessary to introduce damping devices into the system. During the pumping of the working medium through the hose, the inner surface of the corrugation may be torn off. Therefore it is not allowed to use metal hose when velocity of working products is more than 8 m/s for liquids or more than 50 m/s for gases. In the case of applications with high vibration levels the occurrence of resonance vibrations must be prevented.
Working pressure at 20° C is given by dividing the working pressure at the temperature of the medium by the coefficient k, listed in the following table:
|Temperature, ° C
|k coefficient, k
Minimum length of metal hose
|Diameter Dy, mm
|Minimum length of metal hose, mm
Length tolerances of metal hoses
|Length of metal hose, mm
|Diameter over 50 mm
When selecting the length of metal hose it is necessary that it has neutral sections near the fittings, not subject to bending during operation. Hose without neutral sections can be installed only in a straight line or with an offset of no more than 20-30 mm for each meter of length. Stretching, twisting and compression of the hose is not allowed. Maximum deviation of hose length from ratings is 3%. Also bending of smaller radius is not allowed: 10Dy - for hoses with critical application; 5Dy - for hoses with pressure up to 100 atmospheres (10 MPa); 12Dy - for hoses with pressure over 100 atmospheres (10 MPa). Installation should be carried out so as to avoid large loose sections. To avoid sagging, clamps, stands, trays, etc. shall be used. Do not allow deformation of the flexible part of the hose when installing the clamps. To do this, use gaskets of leather, rubber, fluoroplastic and other elastic materials. The connection of the hose with the threaded hose nozzle shall be made in such a way as to avoid turning. When joining the hose with flanged ends and PTFE gaskets should be tightened in pairs crosswise.
Corrugated Metal Hoses
Represents a flexible tube of stainless steel. Depending on the application they are made in different diameters and designed for different working pressures, They are used in industry and construction. In industrial engineering they play the role of fittings, are widely used in ventilation systems as an air vent. In addition, these hoses are used when using flexible hoses for external protection. Sealed corrugated hoses are used to pump water and other liquids.
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