By: Frank Caprio | On: March 6, 2020
Industrial gases have many different origins; some can be manufactured either intentionally or as a byproduct of other processes. Some gases like oxygen are made by natural means such as photosynthesis, while scientists still ponder the cosmic origin of other gases like nitrogen. Most of our helium is found in underground rock formations, where it builds up as a by-product of radioactive decay, and is typically found mixed with natural gas.
Some gases are generated as a by-product of chemical or biological reactions. Carbon dioxide is a great example of this, as it is produced in a variety of ways by many different industries. Most of us are aware that CO2 is generated by burning fossil fuels, but it is also produced when bacteria convert sugars into alcohol during ethanol production. A large amount of CO2 is also produced in a kiln when converting limestone into lime during cement manufacturing. The pulp and paper industry also utilizes lime kilns.
Other gases and liquids are purposely-manufactured using dedicated process equipment. The chlor-alkali industry manufactures chlorine gas by electrolyzing brine, which also happens to produce hydrogen and sodium hydroxide (caustic soda) as co-products.
Whatever their origin, industrial gases must be separated, purified, and compressed for ease of handling. These gases are often packaged in compressed gas cylinders, dewars, and ton containers, all of which are safe, reusable options for transportation and storage. Corrugated metal hoses are commonly used to fill these containers, so let’s discuss proper application, handling, and inspection of hoses in this critical safety application.
Use the “STAMPED” Acronym
When determining the best hose for an application, the STAMPED acronym remains a valuable tool, as it ensures that all operating parameters are considered. However, when filling gas cylinders, it is especially important to accurately specify the pressure, temperature, and flow rate of the media to ensure proper hose selection. Here are some considerations for each of these application variables.
One way to increase the amount of gas that can be stored in a tank is to increase its density by compressing the gas. The LPG tanks we use on our gas grills are pressurized to about 240 psig, and contain about 85% liquid and 15% vapor. However, the large, ultra-high pressure industrial gas cylinders can see gas pressures up to 6000 psi. Few filling hoses can withstand this pressure, and the ones that can aren’t very flexible. Non-metallic hoses are susceptible to permeation through the hose wall, can have coupling retention issues, and cannot handle extreme temperatures, all of which are potential safety hazards. Hose Master’s ultra-high pressure hose, PressureMax HP, provides great flexibility while simultaneously handling pressures up to 6000 psig, with a full 4-to-1 safety factor1. There’s no other hose quite like it for filling gas cylinders.
Once the gas is compressed, it then re-expands during filling operations as it travels through the hose and into the gas cylinder or storage tank. As the gas expands, it cools rapidly. This also causes the transfer hose to cool rapidly, often resulting in frost formation on the hose exterior. We recommend 316L stainless steel hose for inert gas cylinder filling, as it provides excellent resistance to ultra-low temperatures. For more information, refer to our Technical Report on low-temperature hose service. It should be noted that carbon steel fittings should never be used for cryogenic service, as the alloy becomes brittle at sub-zero temperatures.
Certain gas transfer operations may experience quite high flow velocities, which can inflict damage to the hose corrugations if ignored. For these high-velocity applications, a stripwound liner can be added to protect the corrugations from impact by the high-velocity media, extending the service life of the hose assembly. Liners may not always be recommended depending on service conditions, testing requirements, etc. so make sure all application variables are known before recommending a liner.
In addition to the above operating concerns, there are a number of construction and handling issues that also need to be addressed. First, many hoses used for cylinder filling have special end fittings that conform to Compressed Gas Association (CGA) requirements. If transferring flammable gases, then a non-sparking brass fitting is required. These end fittings may require a silver brazing attachment method if welding is not practical due to alloy differences.
Second, we see over-bending as a common cause of failure during cylinder filling operations. This is because the operators tend to use the flexible hose as a handle, making a sharp bend to ease connecting the hose to the cylinder. Adding an interlocked bend restrictor prevents over-bending the hose during hookup or storage. Certain standards also recommend purging the assembly of any media residue prior to storage.
As with any application, the hose should be inspected for signs of damage, broken wires, over-bending, or corrosion. Check the fitting threads and sealing surfaces. Make sure the hose is not overbent during storage, and that it is protected from any potential damage. Critical service hoses may require periodic testing, or possibly replacement after a specific time in service. Because certain gases can penetrate through very small openings, standard leak tests using air under water may not detect a problem. The customer in these instances often specifies Helium Mass Spectrometer Testing of the assembly to ensure leak-free service.
Whatever the application, rest assured that we have a broad selection of products to suit a wide variety of applications, media types, and environments. Don’t be pressured into compromising safety, performance, or reliability. Contact us today to provide the best products at a great value.
1The safety factor is defined as the burst pressure of a hose relative to its maximum allowable working pressure.
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