The invention relates to a process for filling a filling container capable of containing a pressurized fluid with said fluid, especially a pressurized gas bottle, which container is fitted with a regulator of the positive-pressure type, and to its use, in particular in a welding, cutting or similar process.
When carrying out a welding process, especially an MIG (Metal Inert Gas), MAG (Metal Active Gas) or TIG (Tungsten Inert Gas) welding process, it is common practice to use a gaseous shielding atmosphere around the welded zone in order to prevent or minimize the contamination of the welded joint with atmospheric impurities.
This is because it is known that gaseous atmospheric impurities can degrade the properties of a welded joint in the absence of gas shielding.
In particular, hydrogen and water vapor may cause problems of cold cracking of the welded joint.
Likewise, nitrogen tends to degrade the mechanical properties of the joint (Charpy V-notch test) and the presence of oxygen leads to a reduction in the ductility of the welded joint.
However, given that the shielding gases used may themselves also contain impurities of this type, it is necessary to use, as shielding gases, gases of controlled purity, that is to say gases containing an impurity content below a specified maximum threshold, above which the quality of the welded joint produced is no longer acceptable.
Thus, European standard EN 439 recommends that the welding gases must have a water or water-vapor content less than or equal to 40 ppm by volume upon delivery to the user site, that is to say to the customer.
Moreover, similar remarks may be made regarding the gases used in cutting, particularly plasma cutting, in which the quality of the cutting gas has an appreciable influence on the life of the electrode of the plasma torch.
It therefore follows that, at the present time, pressurized fluid containers, such as bottles containing a gas or a gas mixture at a pressure, in general, of 150 bar to 300 bar, usually have, upon delivery to the site of use, impurity contents, particularly water or water-vapor contents, fully in compliance with the maximum permissible thresholds, for example a maximum water or water-vapor content of 40 ppmv.
However, it has been found that as the containers gradually empty, that is to say as the fluid contained therein is gradually used, water or water vapor is deposited on the internal walls of the bottle and, when the pressure within the container becomes less than approximately 70xc3x97105 Pa, water is then entrained by the gas leaving the container.
There is therefore a very marked increase in the water-vapor content in the gas leaving the container, which content may substantially exceed the maximum permissible threshold, that is to say it may exceed 40 ppmv, as shown in the appended figure.
It will be immediately understood that the increase in the water-vapor content of the gas leaving the container has a negative impact on the quality of the welded joint produced, as explained above.
Consequently, the problem that then arises is to be able, as the container empties during use, to guarantee that the water-vapor content of the gas leaving said container is always below the maximum permissible threshold, for example a water-vapor content of at most 40 ppmv, and this being achieved whatever the pressure within the container, that is to say including pressures below approximately 70xc3x97105 Pa.
The solution provided by the present invention is therefore a process for filling a filling container capable of containing pressurized fluid with a fluid, particularly a gas, said container being fitted with a positive-pressure regulator having closure means which impede and/or prevent any inflow and/or any outflow of fluid when the pressure in the bottle falls below a specified positive pressure limit (PPL) value, that is to say a regulator provided with closure means, particularly a valve flap or the like, which shut or stop any flow of fluid, entering or leaving the bottle, when the pressure in the bottle reaches a specified pressure limit value, for example a pressure of less than or equal to 5xc3x97105 Pa, thereby making it possible to prevent the flow of the gas, and therefore any inflow of atmospheric impurities or of air into the container.
According to the process of the invention, a fluid having a water or water-vapor content of less than 40 ppmv is introduced into the container fitted with the positive-pressure regulator, the inside of the filling container having been subjected to a drying operation, prior to introduction of the fluid.
Depending on the case, the filling process of the invention may include one or more of the following characteristics:
the drying operation is carried out by flushing the inside of the bottle with a stream of dry gas;
the drying operation is stopped when the water or water-vapor content in the bottle is below 20 ppmv, preferably below 5 ppmv;
introduction of the fluid into the container is stopped when the pressure exerted in said container is between 100xc3x97105 Pa and 400xc3x97105 Pa, preferably between 150xc3x97105 Pa and 300xc3x97105 Pa;
the fluid is a gas chosen from argon, helium, oxygen, CO2, nitrogen, CO, nitrogen oxides (NxOy), SO2, SF6, xenon, neon, krypton, hydrogen, CH4, SiH4, C2H4 and mixtures thereof, or any other gaseous compound;
a fluid at a pressure of between 105 Pa and 300xc3x97105 Pa is introduced into the container;
the closure means shut for a positive pressure limit (PPL) of greater than 1.5xc3x97105 Pa and of less than 10xc3x97105 Pa, preferably of less than or equal to 5xc3x97105 Pa;
the closure means comprise a valve flap and/or a spring;
the fluid is in liquid and/or gaseous form;
the container is chosen from bottles made of a metal, a metal alloy or a composite, especially bottles made completely or partly of Kevlar(trademark) fibers.
In addition, the invention also relates to the use of a container filled by the filling process of the invention, fitted with a regulator of the positive-pressure type and containing a fluid at a pressure of between 5xc3x97105 Pa and 400xc3x97105 Pa, in a welding operation, particularly a TIG, MIG or MAG welding operation, or a plasma cutting operation.
The invention will now be described in greater detail with the aid of comparative examples and with reference to the appended figures, these being given by way of illustration but implying no limitation.