ALTERNATIVES TO CFC-12 AS A TRACER GAS FOR LEAK DETECTION
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| Overview: |
In order to detect leaks in pressure vessels, refrigeration systems, and various other equipment, the equipment can either be pressurized or evacuated and tested for leaks. Instruments sensitive to certain types of gas are then used to pinpoint leaks in the vessel or system. The repair of small leaks can lead to greater safety and lower product losses, which result in lower costs. Past practice often has been to pressurize a piece of equipment with a refrigerant, such as CFC-12, and then use one of a wide range of refrigerant leak detectors to identify leaks. However, chlorofluorocarbons (CFCs) are significant contributors to ozone depletion, and are therefore being phased out of production. Alternatives to CFCs for leak detection are available for testing the integrity of high-pressure equipment and systems. Several options are available to replace CFC-12 as a leak-detection agent. Options include: a refrigerant and nitrogen/air mixture, a refrigerant alone, or simply an inert gas. Some standard leak detection equipment can detect all leak-detection agent alternatives. Equipment is available that will detect specific concentrations; however, this equipment is very expensive and is not necessary for locating system leaks. Replacement compounds are described briefly below. Replacement Compounds Refrigerant Tracer: In order to use testing equipment, a refrigerant and air, or a refrigerant and nitrogen mixture, is cycled through a system to check for leaks. The reason for having refrigerant present in the leak-detection agent is that it is the presence of a refrigerant makes a leak easily detected. Inert Gases: The use of inert gases for leak detection can be similar to using a refrigerant-based tracer. Inert gases like helium or argon can be used, although special detectors are required. Nitrogen or compressed air can also be used. Others Methods (Soap) Bubble Test: A simple leak test can be performed by applying a soap solution to potential leak sources and observing for bubbles. Dye: Dyes can be applied to suspect areas or mixed into other materials in order to locate leaking areas. Electronic Leak Detectors: Electronic leak detectors can identify the presence of specific refrigerants or gases, and can give a reading on the relative size of the leak. These detectors have movable probes that are effective in areas where a soap bubble test would be difficult. An example of this method of detection is the Refrigeration Leak Monitor (RLM). The RLM is an updated replacement to the Halon monitoring unit that serves both as an automatic safety alarm and a leak detector. This new system detects refrigerant leaks at low levels and reports approximate locations. This monitor aids in the elimination of small leaks while it is small and relatively inexpensive to replace the lost refrigerants. Hydrostatic testing: Hydrostatic testing uses pressurized water as the leak detection agent. This method has limited applicability for leak detection in refrigeration systems and is used primarily for pressure vessels and piping systems. Manometer: Manometers can be used to measure minute changes in pressure across evaporators or condenser coils. While a manometer cannot determine exact locations of leaks, it can identify the section of equipment where refrigerant is being lost. |
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| Compliance Benefit: |
Use of non-ozone depleting substances as tracers such as refrigerants, inert gases, soap, dyes and water will help facilities meet the requirements under 40 CFR 82, Subpart D and Executive Order 12843 requiring federal agencies to maximize the use of safe alternatives to Class I and Class II ozone depleting substances, to the maximum extent practicable. In addition, the elimination of CFC-12 at the facility decreases the possibility that the facility would meet any of the reporting thresholds for CFC-12 under 40 CFR 355, 370 and EO 12856. Chemicals used as substitutions should be reviewed for SARA reporting issues. The compliance benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g. the amount of workload involved.
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| Materials Compatibility: |
Most refrigerants are very inert and have relatively low toxicity. However, some are rather toxic, and others can degrade into toxic materials if they decompose; for example, by exposure to flame. Therefore, leak testing should never present gas concentrations above the compound’s permissible exposure limits unless proper personal protective equipment is used. In addition, chemical compatibility with leak detection equipment should always be checked with the original equipment manufacturer to safeguard components such as gaskets, o-rings, and valve packing.
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| Safety and Health: |
Cylinders which contain nitrogen or compressed air are pressurized to extremely high levels (2,500 to 3,000 psig). Handle all high-pressure gas cylinders with extreme care. Secure all gas cylinders prior to use by chaining or tying to a column or other rigid support. Consult your local Industrial Health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing any leak detection method or product.
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| Benefits: |
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| Disadvantages: |
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| Economic Analysis: |
The most widely used method to detect for refrigerant leaks is through portable leak detectors. Twice a year inspections are made throughout the facility with these detectors. Any leaks that are found are repaired and the refrigerants replaced. The flaw in this system is the lengthy time gaps in between inspections. During these time periods, leakage could occur, causing constant loss of refrigerants until the next inspection. The RLM system, when used in conjunction with portable leak detectors, can locate and eliminate refrigerant leaks at low levels. The RLM, which monitors a specific area constantly, records leaks when they are still relatively small. The RLM then provides an approximate location that is then used by personnel with portable leak detectors to locate the exact area of the leak and repair it. The RLM is a prototype, and has only recently been installed on a few ships. The following data has been obtained from refrigerant leak surveys based on ship data. Mr. Jim Winward of the Naval Surface Warfare Center has provided the RLM data. Assumptions:
Annual Operating Cost Comparison for the RLM and Portable Leak Detectors
Economic Analysis Summary
Capital Cost for Refrigerant Leak Monitor: $5,750,000 Payback Period for Refrigerant Leak Monitor: 3.4 years Click Here to view an Active Spreadsheet for this Economic Analysis and Enter Your Own Values. |
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| Approving Authority: |
Approval is controlled locally and should be implemented only after engineering approval has been granted. Major claimant approval is not required.
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| NSN/MSDS: |
*There are multiple MSDSs for most NSNs. The MSDS (if shown above) is only meant to serve as an example.
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| Points of Contact: |
EPA: Navy:
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| Vendors: |
Spectronics Corporation CEA Instruments,
Inc. Omega Engineering
Inc. Brymill Corporation Spectronics UV-Fluorescent
dye leak detection equipment and materials have been tested and approved
for Navy use by Naval Sea Systems Command. Navy point of contact is Carderock
Division, Naval Surface Warfare Center, Philadelphia Detachment Code 9533
(Attn: Mr. Jim Winward), (215) 897-8783, DSN 443-8783.
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| Sources: |
Mr. Jim Winward, Naval Surface Warfare Center,
Carderock Division, Philadelphia, PA, August 1998. |