# Structural Health Monitoring of Above-Ground Storage Tank Floors by Ultrasonic Guided Wave Excitation on the Tank Wall

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## Abstract

**:**

## 1. Introduction

## 2. Related Work

#### 2.1. Above-Ground Storage Tank Floor Inspection

#### 2.2. Dispersion Curve Calculation for Above-Ground Storage Tank

^{®}Core™ CPU and 16 GB of RAM. The computation time is around 0.01 s per frequency, including the calculation of energy velocity.

## 3. Numerical Investigation

#### 3.1. Numerical Simulation

_{0}) were in the range of 3.125–3.13 mm and calculated as follows,

#### 3.2. Numerical Results

## 4. Experimental Validation

## 5. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 1.**Dispersion curves for a 6.25 mm thick steel plate (

**a**) phase velocity and (

**b**) energy velocity.

**Figure 3.**Layout of the Finite Element Analysis (FEA) model and the point of excitation and reception of both the cases studied.

**Case 1**: excitation and reception from the tank floor; and

**Case 2**: excitation and reception from the tank wall.

**Figure 4.**FEA results: wave propagation at different time increments on a steel 4.1 m diameter, 1 m wall tank at 60 kHz (the tank annular chime is used as the point-of-excitation as illustrated in Figure 3—case 1), and the color scale represents the Von-Mises stress. (

**a**) 67 µs, (

**b**) 267 µs, (

**c**) 467 µs, (

**d**) 667 µs, (

**e**) 767 µs, (

**f**) 867 µs, (

**g**) 1067 µs, (

**h**) 1267 µs.

**Figure 6.**FEA results (Von Mises stress) of ultrasonic guided wave excitation on tank annular chime and tank wall: applied (

**a**) normal stress; (

**b**) shear stress on tank chime; (

**c**) normal stress; and (

**d**) shear stress on tank wall.

**Figure 7.**Normalized time-domain results for both excitation on the tank annular chime and wall; monitored waveforms are labelled according to the Path ID in Table 1. Case 1: (

**a**) normal mode, (

**b**) shear mode; and Case 2: (

**c**) normal mode, (

**d**) shear mode. Results are normalized to the maximum of all 4 signals.

**Figure 8.**Experimental results: contour plot of the frequency sweep (

**a**) in-plane; (

**b**) shear transducers attached on the tank floor to excite guided waves for tank floor inspection with corresponding time-domain representation at 60 kHz; (

**c**) in-plane; and (

**d**) shear.

**Figure 9.**Experimental results: contour plot of the frequency sweep (

**a**) in-plane; (

**b**) shear transducers attached on the tank wall to excite guided waves for tank floor inspection with corresponding time-domain representation at 45 kHz; (

**c**) in-plane; (

**d**) shear.

**Table 1.**Wave paths and analytical Time-of-Arrival (ToA) of potential signals for wave excitation on the tank floor.

Path ID | Path | Distance (m) | ToA ^{1} |
---|---|---|---|

P.1 | Direct path | 4.1 | S0—759 µs |

SH0—1281 µs | |||

A0—1576 µs | |||

P.2 | Wall edge reflection | 6.1 | S0—1138 µs |

SH0—1921 µs | |||

A0—2365 µs | |||

P.3 | Circumferential propagating waves | 6.3 | S0—1166 µs |

P.4 | Around the edge (Rayleigh wave) | 6.5 | 2241 µs |

^{1}Based on the dispersion curves in Figure 1, velocity of S0—5.4 km/s, SH0—3.2 km/s, A0—2.6 km/s.

Case | Mode of Interest | Mode of Excitation | Normalized Amplitude |
---|---|---|---|

1 | S0 | Tank floor | 0.43 |

2 | S0 | Tank wall | 0.05 |

1 | SH0 | Tank floor | 0.33 |

2 | SH0 | Tank wall | 0.25 |

Frequency (kHz) | SNR (dB) | Variation (dB) | SNR (dB) | Variation (dB) | ||
---|---|---|---|---|---|---|

Case 1-S0 | Case 2-S0 | Case 1-SH0 | Case 2-SH0 | |||

40 | 16.5 | 5 | −11.5 | 8.4 | 13.8 | 5.4 |

45 | 9.2 | 1.4 | −7.8 | 13.7 | 21.1 | 7.4 |

50 | 8.1 | 0.4 | −7.7 | 15.9 | 17.4 | 1.5 |

55 | 8.9 | 0.9 | −8 | 19.1 | 16.9 | −2.2 |

60 | 13.1 | 1.9 | −11.2 | 18.1 | 12.4 | −5.7 |

65 | 18.9 | 1.5 | −17.4 | 17.6 | 9.3 | −8.3 |

70 | 17.5 | 4.2 | −13.3 | 11.1 | 6.4 | −4.7 |

**Table 4.**Comparison of theoretical, numerical, and experimental ToA of modes of interest (P.1—direct path).

Frequency (kHz) | Theoretical (µs) | Numerical (µs) | Experimental (µs) | Theoretical to Numerical Error (%) | Theoretical to Experimental Error (%) |
---|---|---|---|---|---|

S0 | 759 | 776 | 723 | 2.2 | 4.7 |

SH0 | 1281 | 1299 | 1242 | 1.4 | 3 |

A0 | 1576 | 1593 | 1533 | 1 | 2.7 |

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**MDPI and ACS Style**

Lowe, P.S.; Duan, W.; Kanfoud, J.; Gan, T.-H.
Structural Health Monitoring of Above-Ground Storage Tank Floors by Ultrasonic Guided Wave Excitation on the Tank Wall. *Sensors* **2017**, *17*, 2542.
https://doi.org/10.3390/s17112542

**AMA Style**

Lowe PS, Duan W, Kanfoud J, Gan T-H.
Structural Health Monitoring of Above-Ground Storage Tank Floors by Ultrasonic Guided Wave Excitation on the Tank Wall. *Sensors*. 2017; 17(11):2542.
https://doi.org/10.3390/s17112542

**Chicago/Turabian Style**

Lowe, Premesh S., Wenbo Duan, Jamil Kanfoud, and Tat-Hean Gan.
2017. "Structural Health Monitoring of Above-Ground Storage Tank Floors by Ultrasonic Guided Wave Excitation on the Tank Wall" *Sensors* 17, no. 11: 2542.
https://doi.org/10.3390/s17112542