**3.3 Monitoring system for storage tanks**

Monitoring of a tank floor is more important compared to the tank wall, due to the fact that degradation of the tank floor is not visible until it becomes severe. A tank floor comprises a large number of plates (dependent on the tank diameter) of 6–8 mm thickness joined with lap welds. SHM of tank floors using UGW is challenging due to this complicated layout, the propagation distance requirement, level of attenuation, and wave reflections and mode conversions at boundaries. GWT of above-ground storage tanks (AST) is an emerging technology and was first explored in 2006 by Mažeika et al. [17]. S0 mode was chosen as the principal mode of interest due to low energy losses from the fluid inside the tank compared to A0 mode [51]. Considering the large area and complexity of tank floor designs, guided waves should be transmitted with as much energy as possible. To achieve full coverage, a Pitch-Catch configuration (through transmission) is preferred for data acquisition and the appropriate transducer array layout was studied by Mažeika et al. [17] and Feng et al. [52].

Transducer bonding is also problematic as the tank annular chime gets heavily corroded over time due to environmental influences. Previous studies on selection of sensor location have evaluated two scenarios: wave excitation on tank annular chime; and tank wall. Currently, normal mode transducers (elongated type) are installed on the annular chime of the tank to transmit guided waves across the floor plate, and a tomographic technique is used to map the structural health of the tank floor [53]. The SH0 mode is an interesting alternative to the S0 mode for this application due to its non-dispersive characteristic [54]. Advances in flexible shear mode transducers led to a recent study [55] on their application to SHM of AST floors. This study evaluated the two modes of interest: S0 mode for normal excitation; and SH0 mode for shear excitations. Sensor location on both the tank wall and annular chime were considered for the two modes. The sensor location is illustrated in **Figure 9**.

The wave propagation for both cases is illustrated in **Figure 10**. A significant amplitude drop for the applied normal load on the tank wall was observed in comparison to the tank floor. However, in the case of shear loading, insignificant amplitude drop was observed.

The application of shear stress on tank wall for guided wave testing of tank floors was thus realised. This increases the potential market for tank floor inspection using UGW as the tank wall can be used to bond shear transducers for structural health monitoring.

**65**

**Figure 10.**

**Figure 9.**

*Monitoring of Critical Metallic Assets in Oil and Gas Industry Using Ultrasonic Guided Waves*

*Schematic of a tank (top) and layout of the point of excitation and reception of the two cases studied (bottom)—excitation and reception from the tank floor in Case 1 and tank wall in Case 2.*

*FEA showing UGW excitation on tank annular chime and tank wall: applied (a) normal and (b) shear stress* 

*on tank chime; and (c) normal and (d) shear stress on tank wall.*

*DOI: http://dx.doi.org/10.5772/intechopen.83366*

**Figure 8.** *Commercial pipeline SHM systems (left to right): MsS [46], gPIMS [48] and iPerm [50].* *Monitoring of Critical Metallic Assets in Oil and Gas Industry Using Ultrasonic Guided Waves DOI: http://dx.doi.org/10.5772/intechopen.83366*

**Figure 9.**

*Advances in Structural Health Monitoring*

**3.3 Monitoring system for storage tanks**

line monitoring devices.

et al. [17] and Feng et al. [52].

illustrated in **Figure 9**.

amplitude drop was observed.

structural health monitoring.

operation and performance is reported [50]. **Figure 8** shows some of these pipe-

Monitoring of a tank floor is more important compared to the tank wall, due to the fact that degradation of the tank floor is not visible until it becomes severe. A tank floor comprises a large number of plates (dependent on the tank diameter) of 6–8 mm thickness joined with lap welds. SHM of tank floors using UGW is challenging due to this complicated layout, the propagation distance requirement, level of attenuation, and wave reflections and mode conversions at boundaries. GWT of above-ground storage tanks (AST) is an emerging technology and was first explored in 2006 by Mažeika et al. [17]. S0 mode was chosen as the principal mode of interest due to low energy losses from the fluid inside the tank compared to A0 mode [51]. Considering the large area and complexity of tank floor designs, guided waves should be transmitted with as much energy as possible. To achieve full coverage, a Pitch-Catch configuration (through transmission) is preferred for data acquisition and the appropriate transducer array layout was studied by Mažeika

Transducer bonding is also problematic as the tank annular chime gets heavily corroded over time due to environmental influences. Previous studies on selection of sensor location have evaluated two scenarios: wave excitation on tank annular chime; and tank wall. Currently, normal mode transducers (elongated type) are installed on the annular chime of the tank to transmit guided waves across the floor plate, and a tomographic technique is used to map the structural health of the tank floor [53]. The SH0 mode is an interesting alternative to the S0 mode for this application due to its non-dispersive characteristic [54]. Advances in flexible shear mode transducers led to a recent study [55] on their application to SHM of AST floors. This study evaluated the two modes of interest: S0 mode for normal excitation; and SH0 mode for shear excitations. Sensor location on both the tank wall and annular chime were considered for the two modes. The sensor location is

The wave propagation for both cases is illustrated in **Figure 10**. A significant amplitude drop for the applied normal load on the tank wall was observed in comparison to the tank floor. However, in the case of shear loading, insignificant

The application of shear stress on tank wall for guided wave testing of tank floors was thus realised. This increases the potential market for tank floor inspection using UGW as the tank wall can be used to bond shear transducers for

*Commercial pipeline SHM systems (left to right): MsS [46], gPIMS [48] and iPerm [50].*

**64**

**Figure 8.**

*Schematic of a tank (top) and layout of the point of excitation and reception of the two cases studied (bottom)—excitation and reception from the tank floor in Case 1 and tank wall in Case 2.*

*FEA showing UGW excitation on tank annular chime and tank wall: applied (a) normal and (b) shear stress on tank chime; and (c) normal and (d) shear stress on tank wall.*
