Even with the proper tools, SF6 gas or sulfur hexafluoride can be difficult to spot in a switchyard. Inspections require a fair amount of patience. And with the newest infrared SF6 gas detectors, it’s important to know the optimal environmental conditions for SF6 gas inspections. For best results in detecting gas leaks, begin your inspection early in the morning beneath a clear cold sky devoid of moving clouds, excessive wind or rain. If you must inspect on a day with cloud cover, aim for total overcast because it can provide a uniform background for temperature comparison. Keep in mind that while clouds can look uniform visually, the bottom can potentially have a different temperature contrast from the rest of the clouds.
Follow these eight steps for capturing gas images:
1. Inspect the right equipment. One of the newest infrared instruments used in utilities, the Fluke Ti450 SF6 Gas Detector, is a test tool for localizing SF6 leaks on equipment where you have confirmed a leak through substantiated evidence. The first thing you should do when you get on site is verify that you are investigating the right equipment and components. Many times, utilities workers will maintain a written log on the inside of the control cabinet door indicating its service history, the dates when SF6 gas was added, and how much gas was added. However, the log will not always tell you where leaks are present. The pre-inspection phase is a visual survey of the equipment susceptible to leaks and an opportunity to devise an inspection plan.
2. Inspect common leak points. You don’t want to randomly search on equipment that does not have a known leak, because that would be the proverbial wild goose chase. Prior to pulling out your specialty infrared detector, do a visual inspection of the equipment and components including the tops and bottoms of bushings, flanges, bolted connections, welds, seals and pressure monitoring tubes. These are common leak locations. During this eye test, look for signs of environmental wear, such as rust or rusting pitting and other forms of corrosion. Welds can deteriorate over time, rust, or not be properly welded. When this equipment is out in the field, it’s going to be exposed to rain and weather elements. Sometimes water will pool and drip from the equipment from different weld points. Rust generally indicates that moisture is getting into the equipment. Any area of corrosion is a potential breach and subsequent leak. In some rainy climates, organic matter (such as mold or mildew) can grow on the outside of the flanges.
3. Mind your background. Every time you encounter a potential leak point, you want to inspect from multiple inspection angles with uniform backgrounds behind the equipment with a different temperature than the gas. The gas inside the equipment will be at the same temperature as the equipment, more or less. So, you want to get a good contrast where you will be able to see a small plume or wisp against a uniform background. This is why you don’t want objects such as trees or clouds in your background, because their movement and varying temperatures make it harder to confirm thermally the presence of SF6 gas. Two examples of good uniform backgrounds are an electrical cabinet, because it is heated and at a different temperature than the gas inside the equipment in the foreground, and a clear cold sky.
Performing SF6 gas inspections
4. Trust your tripod and eye piece. To inspect equipment located up high or down low you will need your camera, which includes a tripod holder and HDMI eye piece—two essential accessories for gas detection. The reason to use a tripod holder is that sometimes it is difficult to establish a good viewing angle unless you’re down on the ground. It’s key to stay aware of where you are and where your equipment is located—don’t fixate solely on the camera display. Similarly, the HDMI eye piece helps you work around viewing from awkward angles and helps minimize sun glare. It also creates the opportunity for team members to view the live camera screen at the same time. Make sure you maintain all safety standards and recommended protocols from the utility where you work.
5. Be patient and methodical. You want to position your camera lower than the leak and point the camera up. At all times, be aware of wind direction and look for gas downwind. If the wind condition is low, the gas will swirl in different directions. Additional tips for performing more accurate inspections include:
• Position the camera and tripod to view each possible leak point with a good background.
• Watch and wait for at least 5-10 seconds before repositioning the camera.
• Use two of the tripod legs for stability on the ground and the other for balancing the tilt of the viewing angle. Tilt slowly from the top of the bushing down to the flange at the bottom.
6. Steady your camera. The camera has two primary modes for viewing gas. The less sensitive is handheld mode, while tripod mode is more sensitive and optimal for capturing wisps of gas when the camera is mounted on a tripod. Even veteran thermographer hands can shake, and the slightest movement can impact gas detector screens. Using a tripod can help generate better results. Note that you can change your IR-Fusion level and save video files in AVI or IS3 formats. While still capture is a functional option for grabbing images, it can be better to take a still frame out of an IS3 video. From this point, you can enhance hand-picked image for presentation.
7. View leaks from multiple angles. It is beneficial to look for all the manmade lines—edges that are part of the equipment vs. objects that are part of the background—because they make it easier to distinguish that movement from a potential leak. You are examining bushings around a seal for unusual movement or plumes that are not moving in the same direction as the clouds. When inspecting, slowly pan down to the bottom, trying to hold the camera as still as possible. Once you view the component from multiple angles, confirming or disconfirming a leak, proceed to the next one, following the same slow and steady process.
8. Stay focused. You’re going to want to make sure the camera is in focus. As you are viewing the scene, it is sometimes disconcerting not to be able to confirm or know what part of the equipment is in view because the display is largely blank. Two options to help with this are to move the camera slightly, which will then show up edges and confirm where you are looking. And secondly, you can use the IR-Fusion function to adjust the IR and the visible blending to provide the reference points of the scene in the display. Operating the camera in full SF6 mode, focus in IR-Fusion and then switch to gas mode. Remember to constantly refocus the camera because you will change your position relative to the component or equipment you are inspecting. If something looks suspicious, try to look at it from a different angle to confirm or disconfirm, and try to look from a closer angle, if possible.