Tank Floor Scanning System (TAFLOSS 2000) tank floor scanning technique for bottom plate, gap & base level contour mapping
In the petroleum, chemical and petrochemical processing plants, gigantic storage tanks are used for temporary storage of crude oil, petroleum products, chemicals etc. The integrity of these storage tanks is an important safety aspect.
Problems such as sagging and uneven or localized sinking are normally encountered in high capacity storage tanks, especially those located on soft ground near the sea-shore. The bottom plate of the tanks are subjected to tremendous stress due to the loading and off-loading activities thus gaps may develop between the bottom plate and the foundation, which in turn can easily generate and propagate cracks. This will eventually lead to leakages and hence financial losses, environmental disturbances and possible fire hazards. Therefore, to ensure safety, storage tanks are regularly emptied for various inspections covering both the tank itself and its foundation.
TAFLOSS 2000, a neutron back-scattering technique coupled with computer-aided analysis, presents an alternative non- destructive method to the destructive, unreliable and time-consuming method of hit and drill, for the
- measurement of the gap between the bottom plate and the base foundation
- detection of the presence of water or leakage of oil beneath the bottom plate of the tanks
- determination of the extent of corrosion of the bottom plate
- mapping of bottom plate and base ground level contour
- The data obtained will enable design and maintenance engineers to decide to either repair the base foundation by grouting, reduce the loading or continue using the tanks without any repair being done.
In view of what the technique can offer, it is highly recommended that a complete inspection programmed be implemented as follows:
- blank inspection - before hydrostatic test of the new tank
- reference inspection - during commissioning
- scheduled inspection - during scheduled maintenance
- revalidation inspection - for life extension evaluation
CASE STUDIES :-
The following are two studies carried out for the oil & gas industry as an indication of what the technique has to offer.
DETERMINATION OF GAPS AND BASE GROUND SURFACE CONFIGURATIONS BENEATH THE BOTTOM PLATE OF CONDENSATE DAY TANK
At the request of a gas company inspection measurements were undertaken on their Condensate Day Tank at its Gas Processing Plant. The inspection was done to determine the gaps between the bottom of the tank floor and its foundation as well as to estimate the content of oil/water present on/in the foundation.
The scanning results revealed irregularities of the bottom plate level. The highest bottom plate level had shifted from its original position. The gap contour indicated there were three locations which had significant gaps. Further evaluation of the results indicated 88% of the gap values were less than 25 mm., and the maximum gap value of 47 mm. was at one location. The water/oil distribution contour showed that most of the areas to be relatively dry except for two inspection points which indicated a relatively higher presence of water/oil content. Based on these results the company will be able to conduct a more effective grouting work later.
DETERMINATION OF GAPS AND BASE GROUND SURFACE CONFIGURATIONS BENEATH THE BOTTOM PLATE OF FUEL STORAGE TANKS
At the request of a power generating station inspection measurements were undertaken on three fuel tanks at their gas turbine project plant. The inspection was done to determine the gaps between the tank floor and its foundation and to estimate the content of oil/water presence on/in the foundation.
The scanning results showed that for Fuel Tank No. 1, the bottom plate contour indicated that the highest bottom plate level had shifted off-center, the gap contour indicated that 61.87% of the gap values were less than 10 mm. but two points were found to have gaps more than 50 mm. and irregularities observed in the base ground contour indicated that the foundation had experienced uneven settlement maybe due to repeated loading and off-loading of the hydrocarbon liquid.
For Fuel Tank No .2, the bottom plate contour revealed that only slight irregularities was observed with the highest bottom plate level appearing at the center of the plot, the gap contour results indicated that 95.68% of the gap values were less than 30 mm. with a maximum gap value of 50.39 mm. at one position and the base ground contour results revealed that the highest level of the foundation was located in the middle of the plot. Nevertheless, the slight irregularities observed in the latter plot indicated that the foundation had experienced uneven settlement maybe due to repeated loading and off-loading of the hydrocarbon liquid.
For Fuel Tank No. 3, the bottom plate contour showed that the bottom plate was in a good level condition, the gap contour showed 70% of the gap values were less than 10 mm. with the maximum gap value of 27 mm at one location and the base ground contour showed the highest level of the foundation was located at the middle and the foundation was in good level condition.
For all three tanks, the foundation seemed to be relatively dry with respect to the water/oil content. The company took note of these results when performing their next grouting works on the respective tanks.
Typical Result of TAFLOSS scan