Questionsandanswers

Gassonic Observer installation

1) Can ultrasonic gas leak detectors replace traditional gas detectors?

Answer: The ultrasonic (acoustic) gas leak detectors can often replace traditional detectors (point/open path) e.g in outdoor gas installations, such as LNG plants and offshore platforms. In other cases, the ultrasonic leak detector will be an add-on to existing gas detection technologies significantly improving the plant safety.

2) Can the ultrasonic gas leak detector indicate a concentration in e.g. LEL for a given gas leak?

Answer: Gas leak detection by means of ultrasound is related to the leak rate and not a gas concentration. In many plant installations the LEL levels are only necessary to indicate if a certain safety level has been exceeded. In most cases the instant on/off indication from the acoustic gas leak detector will be satisfying.

3) Can the ultrasonic gas leak detectors distinguish between different gases?

Answer: No, they will detect all gas releases above a predefined sound level independent of gas type.

4) Will air releases or noise from e.g. choke valves trigger the ultrasonic gas leak detector?

Answer: First of all, normal instrumentation air is only 8-12 BAR. To produce enough pressure to obtain adequate functionality of an ultrasonic gas leak detector, the gas pressure of a leak typically needs to exceed 10 BAR (145 psi). Nonetheless, before implementing an ultrasonic (acoustic) gas detection system, the background noise in the area should be investigated. When the average level of the background noise and the maximum duration of high level noise events are known, the alarm level and the alarm delay can be adjusted to avoid false alarms.

5) What is the normal ultrasonic background noise in plant environment?

Answer: It differs from plant to plant. If noisy machinery (compressors, turbines etc.) is installed in the area to be monitored, the background noise will typically be in the range 64–74 dB. In areas with no noisy machinery (onshore wellhead area e.g.) the background noise will generally not exceed 64 dB. As the background noise may affect the settings and coverage of the ultrasonic (acoustic) gas leak detectors, the background noise should be investigated. Gassonic has authorised and experienced personnel and may be consulted to do onsite plant mapping to estimate ultrasonic background noise levels. Click to read more about background noise and noise mapping survey.  

6) What kind of maintenance does the ultrasonic gas leak detector need?

Answer: The Gassonic gas leak sensors are designed for harsh offshore conditions and they do not have any consumable parts (replaceable sensor heads etc). The detectors have been designed for many years of operations without any kind of replacements. Due to a full SS design microphones are extremely stable compared to infrared and catalytic sensors. If plant maintenance procedures require regular service checks, Gassonic manufactures a Portable Test and Calibration Unit (Gassonic 1701).

7) How can it be verified that the detectors will pick up leaks?

Answer: When commissioning an ultrasonic (acoustic) gas leak detection system, leak simulation can be carried out to verify the performance of the system. Leak simulation is done using Nitrogen and a high pressure hose. Leaks are then generated according to the predefined performance standards (e.g. 0.1 kg/s). This exercise is a service that can be provided by trained Gassonic personnel.

8) How small leaks can be detected by the ultrasonic gas leak detector?

Answer: The gas detection leak rate, which is decisive for the coverage of a Gassonic detector, is primarily a function of hole size and gas pressure. That means that small leaks will be detected with full coverage by the Gassonic detectors if the gas pressure is correspondingly high. E.g. a leak of 2 mm at 140 BAR (ref. methane) will provide a leak rate of 0.1 kg/s and therefore will provide full coverage from the Gassonic detectors. Please consult Gassonic for specific queries.     

9) Can the gas leak detector detect leaks from low-pressure gas systems?

Answer: As a basic rule of thumb, the pressure of the gas system should be at least 10 BAR (145 psi) to provide maximum coverage of the Gassonic gas leak detectors. There is no upper limit. Nonetheless, ultrasonic gas leak detectors can detect gas leaks from pressurized systems kept at much lower pressures. For methane, for instance, a minimum pressure of 2 bar (30 psi) is required to generate ultrasound. Use of the technology in such cases, however, results in reduced detection coverage. Please consult Gassonic for specific queries.    

10) How is the gas leak detector interfaced to the central fire & gas detection system or the plant DCS system?

Answer: The intrinsically safe gas leak detector Gassonic Surveyor has versatile outputs including standard 4-20 mA and various relay outputs. These detectors are connected to the DCS system through EX-barriers or isolators. As the Gassonic Observer gas leak detector is explosion proof it does not need any barriers and can be wired directly to e.g. the fire and gas panel or plant DCS.

11) Can the gas leak detector detect leaks from liquids?

Answer: The Gassonic leak detectors were primarily designed to detect gas leaks but they will also detect certain mixtures of so-called two-phase leaks where gas is mixed with liquids. However, detection coverage for the acoustic gas detectors can be affected. It is not recommended to use ultrasonic gas leak detectors to detect pure liquids as the ultrasonic noise generally will be too low. It is recommended to consult the manufacturer before applying acoustic leak detectors for mixed phase or liquid leaks.

12) Does Gassonic A/S supply portable gas leak detectors?

Answer: At this moment Gassonic A/S only supplies gas leak detectors for fixed installations.

 

 

        The Technology
        Senssonic Self-Test
        North Sea Case Story
        Detection Coverage
        Installation Practice
        Background Noise
        Gas Leak Definition
        FAQ Acoustic Gas Detectors