July 12, 2000
We would like to inform you of a potential pressure hazard associated with cylinders of Anhydrous Hydrogen Fluoride (AHF). This information is being communicated to you to help insure your continued safe use of the product.
In a Product Stewardship Bulletin dated March 1997, Air Products communicated a potential hazard with carbon steel cylinders containing HF. The issue identified in the industry at that time involved the reaction of HF with the iron in carbon steel cylinders to form iron fluoride and hydrogen. The gaseous hydrogen collects in the vapor space and builds pressure over an extended period of time. In order to minimize the possibility that the pressure would build to unsafe levels we recommend that cylinders be pressure checked with a suitable pressure gauge during the recommended maximum two (2) year shelf life period. Cylinders should be returned to the supplier after two (2) years if not being used. The potential exists for pressure excursions of several hundred pounds to occur during the recommended storage time frame. Pressures may continue to rise over longer storage periods. Please avoid this pressure buildup scenario by returning any unused material for proper disposal.
Since our initial communication on this subject, Air Products has conducted in-house testing on this issue of pressure buildup on AHF cylinders over time. We have found that a potential exists for small amounts of H2 to form in AHF cylinders in as little as two days after cylinder fill.
In addition, we want to alert you that some nitrogen may be present as a result of our procedures that involve a N2 purge of our cylinder fill process as an operational safety measure. The presence of the H2(described above) or N2 may result in head pressures in the cylinder higher than the vapor pressure (0.9 psig at 70°F) of the anhydrous HF. These built-up head pressures are well below the maximum allowable working pressure (MAWP) rating of any of our cylinder packages used in Hydrogen Fluoride service if the product is used within its recommended two-year shelf life. (The lowest MAWP for any of our AHF packages is 480 psig.)
Always check the cylinder pressure before connecting it to your process system. Your process system should be equipped with the capability to relieve excess vapor pressure above the normal vapor pressure of 0.9 psig @ 70°F. Vent any excess cylinder head pressure to an acceptable scrubber or disposal system, prior to introducing the AHF product into your production process. We recommend using our Cross-Purge Assembly (E99-CPAM670) and Manual Flow Control Valve (Part number E30-311670) or equivalent. As a minimum, consider a "T" Purge Assembly with a manual control valve. Under no circumstances is the cylinder valve to be used as a pressure-regulating device.
We have reports of users designing their systems for very low pressures commensurate with the low vapor pressure of the AHF of <10 psig. The additional head pressure (described above) may result in the over-pressurization of these customer systems. Although the vapor pressure of the AHF is normally less than 10 psig, depending upon ambient conditions, good engineering practice would dictate that a system be designed for pressures above this level, consistent with any potential pressure excursion that may occur during the operation of the system. You should also consider any potential impact on your operation of using the gas from any AHF cylinder since it may contain hydrogen and nitrogen as well as the AHF. If the presence of either H2 or N2 is undesirable in your process, then vent the head pressure to an appropriate scrubber system prior to commencing operations.
If your facility has carbon steel cylinders containing AHF, you should not store these cylinders for longer than two years. Extreme caution should be taken during the handling of any AHF cylinders that have been stored unused and not pressure checked for periods of time during the recommended two-year shelf life. We recommend a first-in, first-out (FIFO) cylinder inventory practice to minimize storage time. You may opt to return your cylinders to your supplier for disposal of older material. Proper safety procedures should always be used and first aid supplies should be available in the event of personnel exposure.
This communication is consistent with the goals of Responsible Care® and reinforces Air Products' leadership in communicating product stewardship and safety issues to our customers. We encourage you to communicate this information to any others in your location who may have access to the AHF cylinders.
If you have any questions regarding this notification, please contact our Technical Information Center at: 1-800-752-1597.
Contact the Air Products Technical Information Center:
For technical data, product specifications, safety and environmental information, and applications assistance:
Call 1-800-752-1597 (U.S.)
Call 1-610-481-8565 (other locations)
Fax 1-610-481-8690
Email gigmrktg@airproducts.com
Monday–Friday, 8:00 a.m.–5:00 p.m. EST
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