Are there any distance requirements for combustible gas leak detectors when detecting natural gas leaks from pipelines?
1, Principles for detecting natural gas leaks in pipelines
The main component of natural gas is methane, which will diffuse upwards after leakage, and the amount of leakage and environmental wind speed will affect the gas diffusion range. So when using a combustible gas leak alarm for detection, the distance should not be randomly selected, nor should it be the closer the better. It is necessary to combine the sampling method, pipeline location, and environmental conditions of the alarm to find a suitable distance, so as to ensure accurate detection and avoid leakage points.
2, Requirements for detection distance of different types of alarms
There are mainly two types of combustible gas leak alarms: portable and fixed, and their detection distance requirements are different.
The portable combustible gas leak alarm should actively approach the pipeline for detection. For places like pipeline interfaces and valves that are prone to leakage, the sampling port should be aligned with the gap, and the distance should not be too far or too close. If it is too far away, it may not be detected due to gas dilution. If it is too close to the surface of the pipeline, especially when there is oil and dust, it will block the sampling port and affect the results. When inspecting the pipeline body, it is necessary to slowly move along the pipeline, maintain a moderate distance between the sampling port and the pipeline surface, and move too quickly to avoid missing the leakage point. If it is a high-altitude pipeline, the alarm should be raised to a level or slightly higher than the pipeline, and avoid the direction of wind blowing.
Fixed alarm devices are installed in advance, taking into account the coverage of the leakage spread range. In the horizontal direction, it should be installed near risk points such as valves and interfaces, and above the pipeline to facilitate the capture of leaked gases; If it is in a narrow space like a pipeline well, the distance can be appropriately reduced, but do not directly contact the pipeline to prevent vibration damage to the equipment. Vertically, the alarm for overhead pipelines should be installed below, while the alarm for buried pipelines should be installed above the ground, near the projection point directly above the pipeline, and there should be no obstruction on the ground.
3, Key factors affecting detection distance
Firstly, it is the wind speed. During outdoor testing, the wind will cause natural gas to spread rapidly. At this time, a portable combustible gas leak alarm should be used to shorten the distance from the pipeline. It is also necessary to test separately on the upwind and downwind sides, with the upwind side being slightly farther away and the downwind side being closer. Next is the amount of leakage. When there is a large amount of leakage with sound or odor, first locate the approximate area from a distance, and then approach for detection; If the leakage is small and there are no obvious signs, it is necessary to scan the interface gap with a sampling port at close range. In addition, the sampling capability of the alarm also has an impact. Portable alarms with high pumping flow have a wide sampling range and can be extended in distance; If the diffusion flow is small, the distance needs to be shortened.
4, Practical operational suggestions
When detecting a combustible gas leak alarm, multiple measurements can be taken at different distances from the same leak point. If the two values are close and the error is within a reasonable range, it indicates that the results are accurate; If there is a significant difference, check if the sampling port is blocked, if there is any airflow interference, adjust the distance, and then measure again. When moving the alarm, if the value suddenly increases from 0, it indicates that it is close to the leakage point. Slowly reduce the distance until the value stabilizes, and this distance is appropriate; If the value remains 0, you can increase the distance appropriately or measure several points along the pipeline to avoid missed detections.
