Storage Tank – Thermal Image Chronograph
NOTE: Each image is adjusted to provide the best contrast for visual representation of issues being observed. Temperature scales will vary for this reason.
Synopsis
This case study provides a chronological review of the issues found within a customer’s storage tank. The first signs of possible issues within the storage tank were found in thermal images of the north side of the tank (Figure 1). The bean line can be seen just above the warm spot.
Thermal images of north side of tank. Both images show the same spot from different angles.
Thermal images of north side of tank. Both images show the same spot from different angles.
Time Context
Discovery: Wednesday, July 6, 2011
Correction: Saturday, July 30, 2011
Summary of Action
The images in Figure 1 prompted the need for additional imaging within the tank. Images taken from removed air vents on the north side were the first images captured within the storage tank and indicated temperatures in excess of 300°F in the roof support system (Figure 2).
Thermal images of storage tank interior.
Two spots indicating a thermal anomaly were identified on the beans, but later could not be located (Figure 3).
Thermal anomaly in beans.
It was believed that debris had fallen from the roof support and self-extinguished upon contact with the beans.
Images taken on July 7, 2011 from the man access hatch confirmed many of the prior areas seen on July 7, 2000. Several new areas were found, indicating that the issue had spread throughout the tank roof support system (Figure 4).
Areas of concern in storage tank.
Temperatures identified were in excess of 500°F.
In addition, a new thermal anomaly was found on the southwest portion of the roof (Figure 5).
Thermal anomaly in southwest portion of roof.
It was determined that this was above one of the roof supports identified from internal scans. Future scans failed to re-identify this anomaly, indicating that it had moved away from the roof.
Thermal image of beans in storage tank.
Figure 6 is the first image that showed an issue had developed within the beans. The area of increased temperature is clearly seen to be sitting on or near the surface of the beans. Later images showed the progression of this area down into the beans.
Taken one day after discovery, Figure 7 showed that the temperature had increased from 91°F to 173°F.
Changes in thermal anomaly one day after discovery.
Additionally, the area was sitting lower within the beans. As shown in Figure 8, the growth of the increased thermal activity indicated that a much larger area within the tank was involved. This only represented the area directly in contact with the wall of the tank. At this point, nothing was known as to the extent of any issues beyond this area.
Growth of increased thermal activity.
On July 15, the temperature readings on the exterior of the tank were maintaining themselves in the 130°F range (Figure 9).
Temperature readings of exterior of storage tank.
The total area had increased, but appeared to have ceased the initial rapid growth seen in the first few days.
Over the next several days, the tank was filled with nitrogen in an attempt to extinguish any issues within the tank. The large spot on the northeast side of the tank continued to present itself with varying temperatures and sizes, but nothing larger or higher than had been previously seen. The original small spot on the north side also continued to present itself, but there was no increase in temperature or size. For this reason, it was uncertain if this was related to issues within the tank or due to the tank itself.
Internal thermal video screen capture of beans and storage tank.
Figure 10 is a screen capture from an internal thermal video provided by the Gainesville Fire Department that shows a long trail of actively smoldering beans. The upper left portion of this still image is the area just inside the large hot area seen on the tank exterior. The estimated length was over 60 feet.
Storage tank with 500+ gallons of water added.
The screen capture in Figure 11 shows the area adjacent to the tank wall after showering over 500 gallons of water onto the area. While this image appears to indicate a positive result, images taken of the exterior indicated otherwise:
1. Figure 12 was taken at 7:30AM, prior to any water being induced into the tank. The maximum temperature at this time was 154.9°F.
Storage tank before adding water, 7:30AM.
2. Figure 13 was taken at 10:40AM, prior to any water being induced into the tank. The maximum temperature at this time was 176.1°F. This was a normal increase due to solar gain throughout the day.
Storage tank before adding water, 10:40AM.
3. Taken at 11:01AM, 20 minutes into applying water, Figure 14 shows that the exterior temperature had increased almost 30 degrees. Additionally, the area displaying intense heat had greatly increased. The dark blue area to the upper left of the spot shows the water contacting the inside of the tank.
Storage tank after adding water, 11:01AM.
4. By 11:13AM, over 500 gallons of water had been applied onto the beans. The external temperature had increased to 202.9°F (Figure 15). The dark blue area shows where water was applied and indicates that it was not penetrating the beans as expected.
It was decided to end applying water due to the lack of positive results.
Storage tank after adding water, 11:13AM.
One day after applying water, the temperature settled in the mid 120°F range (Figure 16). The larger light blue area was believed to be water surrounding the area and absorbing temperature from the hot beans.
Thermal image taken one day after adding water to the storage tank.
As originally seen, the small spot on the north side of the tank was still present (Figure 17). At this time, it was believed to be an indication of the tail end of the smoldering ribbon seen in the firefighters’ video.
Thermal anomaly on north side of tank after adding water.
Plan of Action
Upon reviewing the application of water to the beans and the tank, it was decided to access and remove the beans from the side of the tank. This task involved cutting a minimum of two holes into the side of Tank 100. The first hole was to be directly over the observed hot spot with the second hole at a point that would allow sufficient draining of the beans. The ability to use infrared imaging ensured accurate placement of both holes and the success of this process.
Figure 18 was taken prior to any holes being cut into the tank. This image shows the extent to which the water had saturated into the beans, as well as the level of the beans. Figure 19 shows issues directly beneath the first hole cut into the tank, while Figure 20 shows greater issues than previously indicated.
Thermal activity prior to cutting holes in tank wall.
Screen shot from the firefighters’ video, taken below first hole.
Based on the information from the first hole, the second hole was determined to be necessary. This hole was to be cut 10 feet to the right of and 10 feet down from the hot spot on the northeast side of the tank. The hole was to be 24 inches in diameter.
Figures 21-30 are a few selected still images and video screen captures taken throughout the day.
Working on storage tank.
22 through 27 were taken during the bean extraction process.
22 through 27 were taken during the bean extraction process.
This screen capture shows one of the final areas inside the tank.
This screen capture shows the same area from Figure 28 as it was being dragged out of the tank. Future imaging failed to find this area.
This screen capture shows the area inside the tank where the hot spot existed. The arrow shows a faint remnant of the previous issue. This small area was removed from the tank.
Supporting Data
A total of 201 still images and 86 videos were recorded. A portion of the images and videos were provided by the Gainesville Fire Department.
All on-site images were captured with a FLIR P660 (s/n 404000174), calibration date December 22, 2010.
Resolution
Thermal imaging was conducted of the internal area of the tank two days after all issues had been removed from Storage Tank 100.
No issues were identified in either the roof supports or the beans.
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