Patent Application
20190242524
The present invention is directed to a high pressure cylinder and, specifically, to a stainless steel high pressure cylinder that provides a stable containment method for reactive gas mixtures in the calibration gas segment of the compressed gas market.
It is known to use extruded aluminum cylinders for storing and shipping high pressure reactive gas mixtures in the calibration gas segment. The aluminum cylinders are limited to a 500 psi operating pressure. Therefore, the aluminum cylinders are not strong enough to handle a large amount of high pressure gas and are not spark resistant.
Water vapor adheres to the interior and exterior cylinder walls via weak intermolecular attractive forces called Van der Waals attraction prior to the cylinder being filled with a reactive gas mixture. The cylinder interior wall is a very uneven surface with nooks, crannies and caverns which also have water adhering to them. Furthermore, the crystal lattice of the metal has interstitial space between its own molecules into which water vapor may adhere. These caverns and interstitial spaces are usually not reachable effectively to remove the water vapor. Thus, each aluminum cylinder must undergo some type of “seasoning” to form a protective barrier between the gas and aluminum cylinder wall. The seasoning process can be either chemical or physical. The seasoning process can take up to three days and may utilize toxic chemicals such as silane to form the protective barrier over the surface irregularities and interstitial spaces to prevent the reactive gas mixture from deteriorating due to the reaction with the water vapor. However, the coating approach does not reach the cavern interiors or the interstitial spaces very well. Therefore, some gas mixes fail at varying periods of time after fill, sometime only taking months to deteriorate.
The present invention is directed to a method for making a cylinder for reactive gas mixtures in the calibration gas segment of the compressed gas market including cutting a stainless steel tube to a desired length. First and second axial end portions of the cut tube are swaged. A spud is connected to the first swaged axial end portion of the cut tube. A base is connected to the second swaged axial end portion of the cut tube.
In another aspect of the present invention a cylinder for reactive gas mixtures in the calibration gas segment of the compressed gas market includes a stainless steel tube having first and second swaged axial end portions and a central portion extending between the first and second swaged axial end portions. A spud is connected to the first swaged axial end portion of the tube. A base is connected to the second swaged axial end portion of the tube.
The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings in which:
A high pressure cylinder 10 for storing and shipping high pressure reactive gas mixtures in the calibration gas segment constructed in accordance with the present invention is illustrated in
The cylinder 10 has a first axial end portion 12 and a second axial end portion 14. A cylindrical central portion 16 extends between the first and second end portions 12, 14. The first and second axial end portions 12 and 14 have a smaller diameter than the central portion 16 and taper from the central portion to the axial ends of the cylinder. The first and second axial end portions may be dome shaped or semi-spherically shaped.
A stainless steel spud or top 20 is welded to the first end portion 12 of the cylinder 10. The spud 20 may have a threaded opening 22 for installing a valve on the cylinder 10. A stainless steel base or bottom 30 is welded to the second end portion 14 of the cylinder 10.
The manufacturing process for the stainless steel cylinder 10 starts with a piece of stainless steel tubing 10 (
The first and second axial end portions 12, 14 of the cut tube 10 are swaged in a press to impart a desired shape to the ends of the tube, as shown in
The spud or top 20 is welded to the first swaged axial end portion 12 of the cylinder 10. The base or bottom 30 is welded to the second swaged axial end portion 14 of the cylinder 10. The cylinder 10 may be tested using a hydrostatic method or a pressure method to ensure that the welds are sound Sample cylinders 10 may be periodically burst-tested at 2.5 to 3 times maximum operating pressure.
The stainless steel cylinder 10 of the present invention requires much less preparation than an aluminum cylinder before filling with a reactive gas mixture. The stainless steel cylinder 10 may be ready for filling once all of the accumulated moisture and hydrocarbon residue is removed from the interior of the cylinder 10. The moisture and hydrocarbon residue that may be present on the interior of the stainless steel cylinder 10 may be removed by heating the cylinder above 212 LF and cleaning the inside wall with a solvent such as alcohol or xylene. The removal of moisture and carbon residue can be concluded in 24-hours or less.
Furthermore, any water vapor remaining in the cylinder 10 may be removed using the following steps before or after a valve is connected to the stub 20. The cylinder 10 is evacuated. After evacuation, the cylinder may be purged with dry N2 to 50 psig, then vented and evacuated. The cylinder 10 is then heated to approximately 200 L-225 LF, at vacuum for approximately 15-30 minutes to remove surface water. The cylinder 10 is then pressurized to a pressure above what the cylinder is rated to hold with a mixture of 2000 ppm CO2 and balance N2 and held at pressure for 5-10 minutes. For example, the cylinder is pressurized to 1400-1500 psig for a cylinder rated to hold gas at 1000-1100 psi. The cylinder 10 may be held at pressure while at a temperature of 200 L-225 LF. While the cylinder 10 is held at 1400-1500 psig, the cylinder expands, creating (otherwise non-existent) entry into any nooks, crannies, caverns and or interstitial spaces.
If a valve is connected to the stub 20, the valve may have a pressure relief device (burst disc CG-1) that is set at 5/3 service pressure +0/−10%. Therefore, the cylinder 10 with a service pressure of 1000-1100 psi may be safely pressurize to 1400-1500 psig without the pressure relief device activating. The valve may also be made of stainless steel, which has its own nooks and crannies/caverns that need to have the water removed and the process removes the water vapor from the valve also.
The wash gas is vented and the cylinder 10 is evacuated and purged twice with dry N2 to 50 psig immediately venting the purge N2 and a final evacuation. At this point the cylinder 10 is ready for filling with a reactive gas mixture.
The stainless steel cylinder 10 is capable of holding pressures in the 1000-1100 psi range. Therefore, the stainless steel cylinder 10 may double the capacity of an aluminum cylinder having the same size. Thus, the reactive gas mixture is provided to the market in a more cost-effective manner on a per psi basis. Additionally, the stainless steel cylinder 10 is considered spark-resistant so that the stainless steel cylinder may be used in areas where safety is paramount, such as, underground mining and offshore oil rigs.
From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/626,316, filed on Feb. 5, 2018, the disclosure of which is entirely incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62626316 | Feb 2018 | US |
