Using MWIR Cameras to Detect and Visualize Hydrocarbon Gas Leaks

Midwave-infrared (MWIR) cameras are used by the oil and gas industries to spot and anticipate the discharge of hydrocarbon gases for example butane, propane and methane.

The unique infrared cameras are developed to take images underneath the red end of the apparent color spectrum at the highest point of absorption wavelengths of the gases. The gases mostly lack a noticeable smell and are unable to be seen by the human eye.

Utilizing MWIR cameras to spot emissions ensures that the welfare of people who work with oil and gas equipment is protected. They also give the ability to swiftly notice any leaks or defective equipment that may be in need of repair. This helps to make the equipment more efficient and cost effective.

Being able to spot problems quickly also defends against the possible negative effects of gas discharges in the environment and reduces the possibility of penalties being applied by environmental agencies.

To detect any hydrocarbon leaks in process control supplies, hand-held MWIR cameras can notice leaks from one to 25 meters with a normal 25 mm fixed-focal-length optic, and can detect many dozen meters when using telephoto lenses.

If a bigger area of detection is necessary, fixed-mounted MWIR cameras on motorized pan and tilt positioners can allow for constant monitoring in 360° for a wide range of protection.

Where workers need to capture transmission and distribution structures for example in remote pipelines, MWIR cameras that are fixed on flying devices such as fixed-wing aircrafts or helicopters controlled from a distance, can help to protect against leaks of up to 500 meters in line-of-sight with the correct lens.

Instead of CCD or CMOS imagers that capture light in wavelengths that are visible to the naked eye, sensors utilized in MWIR cameras notice infrared radiation discharged by objects in the 3 to 5 μm spectral range.

Originally, photon-sensitive focal plane array (FPA) detectors were created from indium gallium arsenide (InGaAs), lead selenide (PbSe), mercury cadmium telluride (MCT), and indium antimonide (InSb).

Midwave-infrared imagers created from InSb are the most frequently used detectors in optical gas imaging cameras because they are more cost-effective in terms of their performance.

While they have a better price to performance ratio, a normal InSb MWIR FPA detector is unfortunate in that it has to be cooled to temperatures of liquid nitrogen in order for it to be photoconductive, and to reduce the noise that would make performance worse otherwise.

This is undertaken by assimilating the focal plane array into a cryogenic cooler and therefore contributes to a bigger size, mass, power consumption and makes the camera more expensive.

SWAP This for That

It is a necessity to lessen the size, weight, and power (SWaP) of MWIR cameras where possible, and this has meant that sensors have been optimized to function at greater temperatures when compared to InSb-based creations, which thereby increases the meantime to failure (MTTF) of these cameras.

Particularly, the proprietary XBn Hot Midwave IR detector established on bulk InAsSb technology has a functioning temperature of around 150 K. This means there is also a comparable decline in the SWaP of the cooler assembly, which uses up less electrical power and also is more effective at cooling down.

Sierra-Olympic Technologies based in Hood River, Oregon, has created an optical gas imaging camera core centered on a XBn Hot Midwave IR detector. The utilization of a 640 x 512, 15 micron pixel-pitch MWIR detector array into the Ventus OGI camera has culminated in a camera with a weight of 580 grams, including the lens.

The XBn Hot Midwave IR detector is based in a vacuum-sealed container referred to as a dewar. The dewar is introduced into a combined detector and cooler assembly (known as an IDCA) which is made up of an optical window, a cold filter and a cold shield.

The central plane of the detector is fixed to an electrical split-Stirling cooler to allow heat to be transferred away. As the split-Sterling linear cooler is of a lighter weight than its cryogenic equivalent, it allows the camera’s weight to be smaller as well, with a smaller footprint and a maximized product lifecycle.

The sterling cooler makes the temperature of the FPA detector smaller, which reduces the possibility of thermal background stray radiation impacting the IR detector. The spectral cold filter fixed in front of the detector also limits radiation from influencing the FPA.

A cold shield was utilized to ensure that the detector is protected from unnecessary heating by IR or thermal radiation rebounding from the dewar in the case of the Ventus OGI camera. The f/1.5 cold shield lets the highest amount of IR energy from a scene to arrive through the lens before encroaching on the detector.

The lenses for infrared cameras with detectors that are cooled must be adapted to the optical design within the cold housing where the IR detector array is based. To target the energy onto the detector to suit the chasm of the cold shield, an f/1.5 lens with a manual focus was created, utilizing unique optical coverings that reduce IR energy to a wavelength area optimized for the narrow band pass cold filter.

Combining the features of the lens and filter allows the camera to notice gas plumes more efficiently.

Camera Characteristics

The XBn Hot Midwave IR detector in the Ventus OGI camera can function at temperatures that are higher than equivalent InSb-based creations, with no negative effects on the integration time, sensitivity, pixel resolution, and the speed of digital data output of each camera.

Frequently, the reactivity of an MWIR camera is characterized as the ratio of the temporal noise to the responsiveness of the camera. This is also referred to as the noise equivalent temperature difference (the NETD). This details the least temperature variation that a camera can solve, and is shown in units of mK.

The acuteness of the optical gas imager from Sierra-Olympic is smaller than 30 mK, an amount that can be compared to InSb and MCT formatted designs. To result in a positive NETD, the MWIR detector utilized in the Ventus OGI camera needs an integration time of between 1 millisecond to 1 second.

Although quicker integration times are thought of as a fundamental feature when taking pictures at high speed, the integration time of the most recent camera does not symbolize a technical disadvantage in the optical gas imaging marketplace.

The MWIR camera’s dimensional resolution, referring to the smallest possible characteristic that it can register, is fixed by the imager’s pixel pitch. The 640 x 512 pixel XBn central plane array utilized in the Ventus OGI entails a 15-micron pixel pitch.

Sensor manufacturers are creating devices at the moment with a 10 μm XBn pixel pitch, which are similarly created to function at 150 K with an efficiency that is equivalent to the 15 μm pixel pitch design.

To help with the range of applications, the Ventus OGI which operates at 30 frames-per-second (fps), can come with various output options. Interfaces include a 14-bit CameraLink interface, NTSC or PAL analog video, and an RS-422 serial interface for better control of the camera.

A customized option is present to allow users with a H.264-encoded IP stream or GigE Vision interface which entails both video and camera control.

Software Support

The setting and determination of image data is a fundamental feature in noticing fugitive emissions. To meet this requirement, a refined software tool is available with sophisticated processing features. A document API (application programming interface) helps developers in combining downstream software.

In some circumstances, there might be only a small difference in temperature from the target and the background image. Mostly, it is preferable to have a 5 degrees Celsius temperature variation between a gas plume and the background.

When this does not happen, dynamic contrast optimization and tools that help the reduction of noise can help the user to better capture the plume. Automatic Gain Control (AGC) can format the brightness and contrast on local areas of the image founded on the distribution of thermal intensity.

The foreground and background contrast of images can be changed independently from one another. In the example detailed above, the boost of foreground could enhance the contrast of the gas plume, while the boost of background would show more of the equipment detail and the local area.

Many gas imaging cameras use monochrome or grayscale palettes to detail the captured images. Figure 2 is a frame capture of gas discharge resulting from a midwave infrared OGI camera. Warmer areas of the image are shown in white, whereas cooler areas are shown as the black color.

It is worth noting that various other visualization features are available to the user when utilizing the Ventus OGI. Users can swap the polarity of the image that is monochrome where black becomes warm and white becomes cooler. On the other hand, users can select from various rainbow, ironbow, or sepia palettes, which determine various colors to show various infrared intensity.

Unmanned Drones

The Ventus OGI camera is revolutionary in terms of the manufacture of MWIR cameras. It is the most delicate, light in weight, and power efficient OGI camera that is available to purchase. It weighs 580 grams with a lens, and its size is 146.6 x 70.9 x 73.1 mm.

The Ventus OGI shows a massive enhancement when compared to older creations that were often almost double in size and in weight.

The Ventus OGI camera is low SWaP, and more recently it has been EPA 0000a CERTIFIED, and is compatible to use on multiple rotor or fixed wing unmanned aerial vehicles (also known as UAVs), where they can be utilized to observe areas in plants for gas processing and pipe racks.

This also reduces the necessity for personnel to carry out tasks that are manual, which results in more efficiency and reduces the costs of managing operations.

Surveillance using aerial devices is a great method in carrying out checks on wide sections of pipelines (Figure 3). More often than not this has been a function carried out by helicopters that are manned, which therefore requires a pilot and an operator for the camera.

With the Ventus OGI, wide-ranging surveillance procedures can be operated by unmanned drones, which carry out tasks more efficiently and are also more cost effective to utilize.

This information has been sourced, reviewed and adapted from materials provided by Sierra-Olympic.

For more information on this source, please visit Sierra-Olympic.

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