May 26 Read May 25 Read May 14 Read May 13 Read Apr 30 Read Jan 17 Read
|Published (Last):||2 July 2004|
|PDF File Size:||2.98 Mb|
|ePub File Size:||3.33 Mb|
|Price:||Free* [*Free Regsitration Required]|
Field trials have indicated that gas plumes in well ventilated areas may not be detected by fixed point or open path detectors. The potential therefore exists for gas from undetected leaks to disperse to adjacent areas, accumulate in ventilation dead spots in the modules, or for the release to continue undetected for some time Figure 1: Ultrasonic gas leak detectors do not need physical contact with the gas. They are unaffected by wind, gas dilution, and the direction of the gas plume.
Contents Introduction. LEL vs Leak Rate. How to Interface Detectors with the Control System. Acoustic Self-Test Self-Diagnostics. Such application of the. The document is meant to be an active document, which will be updated frequently as more knowledge is gained. Reference HSE. Fire and Explosion Strategy, Issue 1. Hazardous Installations Directorate, Offshore Division. Fixed gas detection in open ventilated areas like offshore or onshore oil and gas facilities is generally considered problematic because the gas easily dilutes and drifts away from conventional gas sensors.
Ultrasonic gas leak detectors solve this problem by detecting the airborne acoustic ultrasound generated when pressurized gas escapes from a leak. When a gas leak occurs, the ultrasound generated by the leak travels at the speed of sound, through the air, from the source to the detector.
Ultrasonic gas leak detectors are non-concentration based detectors. They send a signal to the control system indicating the onset of a leak. Figure 2. The gas release event tree illustrates the sequence of events that can take place in the event of a gas release.
The figure shows that UGLD responds at gas leak initiation whereas conventional detectors only respond when the gas has accumulated and formed a vapour cloud. After the gas leak begins,. The total response time for UGLD and conventional gas detectors. If the gas leak takes place inside a building, the gas can quickly accumulate and prompt a point or open path detector to alarm. However, if the gas leak is outdoors or where the air current is strong, it may.
This can be difficult in open, well ventilated areas where. Conventional Gas Detectors When it comes to the response time of a conventional gas detection system, it is important to consider the total. Tdetector is normally seconds. Tgas tells how long it takes for a certain gas concentration. In practice, Tgas can range from minutes to hours! Tultrasound represents the time it takes ultrasonic noise to travel from the leak source to the detector.
This is typically measured in milliseconds. In a safety system with gas detectors, it is inadequate to use just Tdetector. One must consider the total speed of response, Ttotal, which is the only parameter that provides a true picture of the actual response time of the gas detection system.
Ultrasonic gas leak detectors. The response of the UGLD is not dependent on the gas to travel to the detector, which means that it reacts much faster to the dangerous gas leak. Figure 3 on the opposite page illustrates the superior Ttotal for an ultrasonic gas leak detector.
The main advantage of an UGLD compared to a conventional gas detector is that it does not need to wait for a gas concentration to accumulate and form a potentially explosive cloud before it can detect the leak. Figure 4. The graphic shows the detection coverage characteristics for UGLD. The distances are based on the detection of methane based gas leaks using a leak rate of 0. Page For the purposes of sensor allocation, plant.
A more detailed description of specific noise levels and sensor implementation follows in Chapter 4. The image shows a detector installed on a mounting pole 2 meters 6 feet above ground as seen from the front. Because the sensor points down when installed, the detection coverage is greater below and to the sides of the sensor than above. Detection coverage for high, low, and very low noise levels is illustrated in the figures below.
Coverage is based on detection of methane leaks using a leak rate of 0. LEL Vs Leak rate Whereas conventional gas detectors measure gas concentrations as a percentage of the lower explosive limit LEL or in parts per million ppm , the performance of ultrasonic gas leak detectors is based on the leak rate, usually measured in kilograms per second.
Figure 6: The conventional gas detector above measures gas concentration in the lower explosive limit LEL. The LEL level measured by the sensor depends on the leak rate mass flow rate , leak directionality, and where the sensor is positioned relative to the leak. Guidelines for other gases are found in Chapter 2. Gas pressure, leak size and detection coverage Gas pressure and influence on UGLD The detection coverage illustrated in the previous section is based on a gas pressure of at least 10 bar psi.
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. For allocation of UGLDs in low pressure systems the manufacturer should be consulted. Figure 7. Instead of considering specific hole sizes or pressures, UGLD should be related to the leak rate.
The most important thing to understand is that the leak rate can derive from an infinite number of combinations of leak size and gas pressure gas properties also have some influence. As the hole becomes larger, the leak rate increases. When the system pressure starts dropping it causes a reduction of the leak rate and thereby decrease the ultrasonic sound level.
In theory, there is no limitation to the rule when the leak becomes small. However, to achieve the commonly used leak rate for methane of 0. Figure 8. When the pressure is kept constant a small leak has a smaller leak rate and makes less ultrasound compared to a bigger leak.
Frequency and AMPLITUDE Ultrasonic gas leak detection differs from conventional gas detection mainly because it responds to the airborne acoustic sound from the gas leak, and not by sensing the gas molecules. The UGLD is designed to ignore audible and. Basically it depends on the process equipment installed in various parts of the plant.
In some areas there is a complex mixture of sound frequencies at high amplitude high dB level ;. Are there any installations where UGLD cannot be used? Ultrasonic gas leak detection is only applicable when the gas is under pressure because it is the drop to atmospheric pressure that makes the leak generate ultrasound.
Making UGLD part of the plant fire and gas detection system adds an alternative or complementary layer of protection, which may increase detection efficiency while reducing the need for a high point sensor count. As the UGLD technology is based on sound propagation instead of transport of gas molecules, detectors respond to hazards at a significantly faster rate than concentrationbased sensors. The detectors are unaffected by environmental conditions like wind, leak dilution, and the direction of the leak, which indicate that they have high detection reliability.
The box to the right lists the most important benefits of applying UGLD. Ultrasonic gas leak detectors can be used for any application that contains pressurized gas since UGLDs detect the leak and not the gas plume.
Figure Lighter gas molecules typically create higher levels of ultrasound at the same leak rate. Which gases can UGLD detect? Ultrasonic gas leak detectors can be used for any application that contains pressurized gas since the UGLDs respond to the leak noise and not the gas itself.
Ultrasonic gas leak detectors respond to leaks when gas. Tests carried out by General. In extremely cold environments special attention should For standard applications and standard coverage, the gas.
As previously mentioned, the specific gas properties influence detection coverage. In general,. This CO2 gas generates high levels of. Due to its chemical properties, hydrogen poses unique challenges in the plant environment.
Hydrogen gas is. Reservoirs that contain high concentrations of H2S are likely to hold a mixture of gases and liquids. It shows. The implementation practice chapter. The trigger level is then set to 84 dB or a corresponding value in mA see also. It may also be used for detection of propane. For further input it is recommended to contact a Gassonic or General. It should be noted that the detection coverage is based on. It should also be noted that the information on these pages should be seen as guidelines only and.
How can UGLD work in noisy plant environments? The detectors can be installed in noisy environments because the technology only responds to high frequency noise.
Ultrasonic gas leak detector handbook
Field trials have indicated that gas plumes in well ventilated areas may not be detected by fixed point or open path detectors. The potential therefore exists for gas from undetected leaks to disperse to adjacent areas, accumulate in ventilation dead spots in the modules, or for the release to continue undetected for some time Figure 1: Ultrasonic gas leak detectors do not need physical contact with the gas. They are unaffected by wind, gas dilution, and the direction of the gas plume. Contents Introduction.
New technical handbook on ultrasonic gas leak detection
The handbook presents applications data with respect to specific gases and application locations. It also provides step-by-step guidelines on how to integrate these detectors into safety systems based on plant layouts, detection coverage, voting with other detector types, and other important considerations. Utilising the whole range of sensing technologies enhances detection capabilities and reduces risk because leaks are detected with greater speed and confidence. Ultrasonic gas leak detectors are used in pressurized gas applications to complement conventional gas detection methods. In outdoor or ventilated locations, conventional detectors can miss gas leaks due to wind conditions, gas dilution, or leak directionality. To compensate for such situations, ultrasonic gas leak detectors pick up gas leaks by responding to the airborne ultrasound instead of relying on physical contact between the gas and the sensor element. This capability significantly improves total speed of response to dangerous gas leaks.
Observer-i Ultrasonic Gas Leak Detector