Patent Application
20130206778
The invention refers to field of gas fittings, namely, metal composite pressure cylinders, used in particular for portable oxygen breathing apparatus for climbers, rescue workers, in portable devices of cryogenic and fire-fighting equipment, gas supply systems, automotive and other industries.
These cylinders (vessels) are designed for storage and transport of fluid (liquid or gas) under high pressure. Such vessels are usually exposed to repetitive cyclic high pressure loading.
In the cylinders of this type, the material of insulating overwrap, liner, is of great importance, for it is necessary to prevent fluid leakage or loss of sealing. The liner is fabricated from thermoplastic, aluminium, or steel depending on the type and character of the fluid that fills the vessel. Currently cylinders with metal liners are most widely used, for they have a number of advantages compared to plastics.
Currently available metal composite high pressure cylinders contain internal thin metal sealed overwrap, a liner, and outer pressure overwrap made of composite material formed by winding in different directions on the surface of the liner of high modulus fibre cords (e.g. carbon fibre) impregnated with a binder.
In accordance with the requirements of the current regulatory documents, in addition to the basic requirements to high pressure gas cylinders, decrease of specific consumption of materials and safe operation, there is also a basic requirement to ensure a long lifetime of a cylinder determined by the number of load cycles. Unlike other types of cylinders, this requirement is crucial for the composite metal cylinder structure, because of high heterogeneity of physical and mechanical properties of the materials. The third, also crucial requirement specified in the cylinders regulatory documents is the requirement of a reliable fixing of the cylinder neck choke in a composite overwrap that also provides its multiple torsional loads.
There are numerous examples of composite pressure cylinders with metal liners made of various alloys (see, e.g., U.S. Pat. Nos. 5,494,188, 5,538,680, 5,653,358, 5,862,938, 5,938,209, 5,979,692, 6,190,598, 6,202,674, 6,202,674, 6,230,922).
However, these constructions cannot completely provide a solution of main targets with regard to the cylinder construction: reliability under heavy high pressure cyclic loading in combination with minimum weight and manufacturing cost comparable or lower than those of all-metal cylinders.
There are numerous examples of composite pressure cylinders with thin metal liners made of various alloys (see, e.g., U.S. Pat. Nos. 3,066,822, 3,446,385, 5,292,027, 5,822,838, 5,918,759, WO 03/029718), which allows to partially solve the problem of more heavy high pressure cyclic loading in combination with the weight which is lower than that of all-metal cylinders.
There are numerous design solutions of metal composite cylinders with thin liners, using a variety of methods of the alignment of deformation of the liner material and composite overwrap.
In the construction described in application RU No 2001115743 for high-pressure cylinder containing composite overwrap and a thin metal liner, the set problem is solved as follows: the liner wall thickness and composite overwrap thickness are selected based on the assumption that the cylinder main bearing element is a composite overwrap, and the material of metal liner under working pressure is in elastic range. The drawback of this solution is That due to large difference in the values of the limits of fracture deformation of composite material (up to 2%) and the elastic deformation of metal (0.2%), the weight of the construction and its cost are very high, that makes this type of the cylinder non-competitive compared to its metal equivalents.
The construction of the cylinder as per patent RU No 2094695 suggests the use of a metal liner, made with the longitudinal and circumferential corrugations. In this case the external cavities of longitudinal corrugations can be filled with elastic material. Elastomer is used as elastic material.
The drawback of this solution is the following: the construction of the liner designed as a set of longitudinal and circumferential corrugations, increases the general flexural rigidity of the liner, but does not meet the conditions of compatibility of deformations in the material of liner and in the material of composite overwrap. Plastic deformations occur in corrugations under cyclic loading that leads to premature destruction of the liner.
The prototype of the proposed invention is a solution described in patent RU 2358187 C2, 10.09.2008, suggesting to use a liner made a smooth and thin metal, and to select the material for pressure composite overwrap taking into account a specified ratio with regard to geometry and material to the liner.
The drawback of this solution is the following: a criterion of the compatibility of the deformation of heterogeneous construction materials is used as the design criteria for cylinders design,
but the construction made with the proposed size ratio does not meet the requirements of the cylinder lifetime with regard to cyclic loading.
The objective of the invention is to select a material and pattern of reinforcement of forming layers groups to ensure a minimum weight of the construction for the known liner material, taking into account the restrictions for the level of plastic deformation of the liner material.
The technical result of the invention is that the proposed cylinder construction provides high performance at any given level of cyclic high-pressure and torsional loading with minimum weight and manufacturing cost. The advantage of this solution is that the proposed cylinder construction provides the desired lifetime of the cylinder. In addition, there is a real possibility to get an efficient construction with use of the materials of a liner and pressure overwrap depending on the type of the materials. The possibility of high plastic deformations in a liner ultimately leads to the phenomenon of low-cycle material fatigue of the liner. The proposed design of the cylinder meets the requirements of a secure fixing of the cylinder neck choke in the composite overwrap that provides multiple torsional loads.
The technical result is achieved by the following: a metal composite cylinder contains a cylindrical metal liner with profiled bottoms and neck flange with a choke fixed in a pole hole of the pressure overwrap, made of composite material formed by a group of layers of reinforcing filaments orientated in spiral and, circumferential directions, with different reinforcing capacity; at that, combination reinforcing capacity and thickness-wise distribution of groups of reinforcing material layers of the pressure overwrap provide the deformation intensity in each point of the liner material that meets the following condition:
Individual groups of layers of reinforcing material filaments of the pressure overwrap orientated in the spiral directions are a part of the annual band material.
Annular band may be fabricated from the materials with higher modulus of elasticity compared to the material of pressure overwrap.
The annular band may be made of materials with different moduli with layered distribution along the diameter of the band.
Annular band fixing grooves may have a polyhedron shape.
Annular band fixing grooves may have an ellipse shape.
The flange collar may be labelled with identification and technical information.
The flange collar may be fabricated as a separate ring rigidly connected to the flange choke.
The outer surface of the annular flange may be with taper towards the collar.
The bottoms of the pressure overwrap formed by a group of layers of reinforcing material filaments orientated in spiral directions, and a cylindrical part formed by a combination of groups of layers of reinforcing material filaments orientated in spiral and circumferential directions, may be aligned in the zone of their junction with regard to annular deformation.
It is commonly known, the current design methods of the cylinders are based on the laws of the strength under static loading, with some corrections considering the characteristics of the used material and construction. Such corrections include load and safety factors.
At the same time, main provisions of mechanics of solids state that the governing conditions for the destruction of the material of the cylinder construction under consideration, under static loading, provide for some limiting surface involved in the moment of destruction.
Current methods do not consider the way of this surface involvement. At the same time, the targeted operational safety of the cylinder is related to the peculiarities of behaviour of metals and alloys used in the construction of cylinders under cyclic deformation, since it determines the so-called fatigue or loading history of the construction.
Fatigue of a construction is a process of gradual accumulation of damage in its material due to the effect of cyclic loads. This particular fatigue is a major cause of destruction of the cylinder construction under consideration or pressure vessels. It is characteristic of fatigue failure that it can have a long incubation period, sometimes years of the device operation during which the detection of signs of impending failure is difficult.
Thus, cyclic and long-term loading of a cylinder construction results in damages accumulated in a metal liner that occur differently, in different ranges of applied stresses.
Obviously, an efficient construction, presupposes the more effective use of high strength characteristics of composite material, i.e. a high level of plastic deformation should be in the liner that eventually results in the phenomenon of low-cycle fatigue of the liner material.
Low-cycle fatigue is characterized by plastic deformations in macroscopic volumes of the liner material in each loading cycle. Low-cycle fatigue occurs when maximum stress exceeds the yield limit of the material, and is accompanied by alternating plastic deformation of the material volume which is larger compared to the size of structural components (grains, pores, inclusions).
The number of cycles before the formation of visible cracks depends largely on the size of plastic deformation of the material in each cycle and on the ability of the material to resist the low-cycle destruction. The behaviour of the material is determined by Bauschinger effect, cyclic hardening or softening of the material (i.e., change in hysteresis loop size and shape with an increase in the cycles number), as well as residual stresses in the construction formed by the incompatibility of plastic deformations.
Main characteristics of plastic deformation process in the point of a body under changes of cyclic loading with the period T is an increment of plastic deformation per cycle
(here, εp is the rate of plastic deformation, τ is time from the beginning of the cycle), and amplitude of plastic deformation per cycle
δεp=εp max−εp min.
The increments and amplitude of plastic deformation as well as plastic hysteresis loop shape and size are different in different points of the construction and usually vary from cycle to cycle.
As a rule, plastic as well as elastic deformations arise in the material of the liner of the cylinder construction under cyclic loading.
For a large number of metals and alloys in the transition area, when it is necessary to take into account both plastic and elastic deformations of the liner material in order to describe the relationships between a number of cycles to failure Nf and deformation amplitude of low-cycle fatigue, the following types of experimental approximating functions can be used
Taking into account the mentioned above, the task of the cylinder design can be expressed by the following statement: it is necessary to select a material and pattern of reinforcement of forming layers groups to ensure a minimum weight of the construction for the known liner material, taking into account the restrictions for the level of plastic deformation of the liner material represented as a condition
The set task may be solved in the following way. The construction deformations in circumferential and meridional directions are calculated by known methods for a given load (e.g., an internal test pressure) for the regular distribution of groups of filaments layers, reinforcing materials and their capacity orientated in spiral and circumferential directions of reinforcement in each section of the construction. Based on the data obtained and using the relationship
intensity of deformations εi, and intensity of stress σi in the liner material are calculated. Then, using the principle of unified curve of deformation of the liner material, the value of intensity of the liner deformation in compared to limitation εi≦εa for the construction under consideration. When this limitation is met, the construction obtained meets the regulatory requirements with regard to strength as well as operational lifetime.
The construction of minimum weight is selected based on a varying such solutions of distribution of combination of reinforcement capacity and distribution of groups of reinforcing material layers. Thus, the design of the cylinder meets the condition that the combination reinforcing capacity and thickness-like distribution of groups of reinforcing material layers of the pressure overwrap, provides the intensity of deformation in each point of the material liner less than
(where N is a required number of trouble-free operation cycles of the cylinder loaded at working pressure, σB is a temporary resistance, ψ is a limit of contraction area and E is a modulus of elasticity of the liner material), is an optimal construction.
On the other hand, a reliable operation of the construction is impossible without the cylinder neck area design ensuring reliable operation of the mount flange.
This design solution in represented in
Combination of reinforcing capacity and thickness-wise distribution of groups of reinforcing material layers of the pressure overwrap provide the deformation intensity in each point of the liner material meeting the following condition:
Neck flange 3 of the liner is equipped with collar 4 on the side of the open end of the choke, with an outer diameter greater than the sum of the pole hole diameter of the composite overwrap and two widths of wound, filaments of reinforcing material, so that
concentric annular cavity is formed between the outer surface of the composite overwrap and the flange, where annular band 5 is located filling the entire volume of the cavity; the band is made of the material of the composite overwrap. Choke of neck flange 3 is fixed in annular band 5 with grooves of non-circular shape.
Individual groups of layers of reinforcing material filaments of pressure overwrap 2 orientated in spiral directions are a part of the annual band material. Annular band 5 may be fabricated from the materials with higher modulus of elasticity compared to the material of pressure overwrap. Annular band 5 may be made of materials with different moduli with layered distribution along the diameter of the band. Annular band 5 fixing grooves may have polyhedron or ellipse shape. Flange collar 4 may be labelled with identification and technical information. The flange collar may be fabricated as a separate ring rigidly connected to the flange choke. The outer surface of annular flange 3 in the zone of the choke may be, designed with a taper towards the collar.
The bottoms of pressure overwrap 3 formed by a group of layers of reinforcing material filaments orientated in the spiral directions, and a cylindrical part formed by a combination of groups of layers of reinforcing material filaments orientated in spiral and the circumferential direction, may be aligned in the zone of their junction with regard to annular deformation.
The proposed solution functions as follows: when the pressure overwrap is fabricated by winding method, thickening is formed in the zone of a pole hole. Usually the diameter of the thickening is the sum of the diameter of the pole hole, in which the flange choke is placed and two widths of technological tape of reinforcing material. Above this diameter, there is a smooth wall thickness change of the pressure overwrap due to continuous winding process. When the overwrap is deformed without the band, the overwrap pole hole opens and makes free movement of the flange possible. The band introduction allows controlling the process of the overwrap deformation in a specified zone, and thus, it allows creating a reliable connection of the overwrap and liner in the pole hole.
In addition, the band dramatically reduces the stress arising in the pipe of the flange that allows reducing the total weight of the flange construction. The efficiency of the construction under consideration can be significantly increased due to fabrication of the band from the heterogeneous materials 6-9 (see
Operation of high-pressure cylinder is in the filling it with fluid (liquid or gas) to the required level of pressure, storage, transport, emptying, subsequent new filling, the fluid expenditure, i.e. in the repetition of actions and operations with multiple cyclic loading.
The proposed device provides a real opportunity to use high-pressure vessels made of different materials with use of welded thin metal inner overwrap, liner. Fabrication and testing of high-pressure vessels with the proposed liner for their sealing, confirmed their high reliability and efficiency. Proposed cylinders may be used in portable oxygen breathing apparatus for climbers, rescue workers, in portable devices of cryogenic and fire-fighting equipment, gas supply systems, automotive and other industries.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/RU10/00034 | 2/1/2010 | WO | 00 | 10/29/2012 |
