Tank integrity is vital for the safe storage of drinking water. Inspections related to tank integrity are designed to assess the condition of the tank and prevent leaks, structural failures, or complete tank rupture. The types of inspections related to tank integrity include:
- Visual Inspections: Routine visual inspections are performed to check for obvious signs of wear, corrosion, deformation, or other physical damage to the tank’s interior and exterior surfaces. These inspections are usually the first step in assessing tank integrity.
A common type of visual inspection conducted today is a drone inspection. Drones limit and, in some cases, eliminate the need for climbing a tank depending on what is being inspected. However, it’s more common for a tank inspection to require a mix of human visual inspection from climbing and drone imagery. Drones are particularly helpful for getting close up imagery of equipment on the side of tanks such as collocated cell antennas, conduit, and the overflow pipes. Drones are also helpful at detecting structural issues such as signs of buckling by allowing inspectors to see the tank from much higher than their field of view. Drones are also helpful in determining issues with coatings by capturing imagery that covers wider sections of the tank than can be viewed by the human eye.
- Ultrasonic Thickness Testing (UTT): UTT is a common non-destructive testing method used to measure the thickness of the tank walls. By sending ultrasonic waves through the tank material, inspectors can detect thinning due to corrosion or other forms of degradation, which might compromise the tank’s integrity.
- Magnetic Flux Leakage (MFL) Testing: MFL is used to detect corrosion, pitting, and other forms of degradation in ferromagnetic materials. It involves applying a magnetic field to the tank wall and then using sensors to detect any leakage in the magnetic field, which indicates the presence of defects.
- Radiographic Testing (RT): This method uses X-rays or gamma rays to produce images of the tank’s structure. RT is effective for detecting internal defects like cracks, voids, or inclusions within the tank walls that are not visible from the outside.
- Hydrostatic Testing: This test involves filling the tank with water or another liquid to check for leaks and to ensure that the tank can withstand its intended pressure load. Hydrostatic testing is often required after a tank is constructed, repaired, or modified.
- Leak Testing: Various leak detection methods, such as pressure testing, dye testing, and acoustic emission testing, are used to detect leaks in tanks. Leak testing is critical for ensuring that the contents of the tank are securely contained.
- Vibration Analysis: Vibration analysis can detect structural weaknesses in the tank or its supporting structure. Abnormal vibrations can indicate issues such as cracks, loose components, or alignment problems that might affect the tank’s integrity.
- Settlement Monitoring: Over time, the ground beneath a tank can settle or shift, leading to structural stresses. Settlement monitoring involves measuring any movement in the tank’s foundation or surrounding soil to ensure it remains stable and level.
- Cathodic Protection Inspection: For tanks with cathodic protection systems, regular inspections are necessary to ensure the system is functioning correctly and preventing corrosion. This might involve measuring the electrical potential of the tank and surrounding soil.
- Internal Inspections: When the tank is taken out of service, internal inspections are conducted to assess the condition of the interior surfaces. Inspectors look for signs of corrosion, pitting, coating degradation, or other issues that could compromise the tank’s integrity.
When the tank is left in service, underwater ROV and dive inspections can be used. With both types, the interior of the tank is inspected by capturing video and images while the tank is full. For underwater ROV inspections, an operator controls the ROV remotely from outside of the tank. For dive inspections, industrial SCUBA divers enter the tank. In both cases, there are numerous safety and regulatory considerations for potable inspections that are to be discussed in other sections.
- Acoustic Emission Testing (AET): AET is a non-destructive testing method that listens for high-frequency sound waves emitted by active cracks or defects within the tank. This method is particularly useful for detecting real-time changes in the tank’s structural integrity.
- Infrared Thermography: Infrared cameras are used to detect temperature variations on the tank’s surface, which can indicate issues like leaks.
- Strain Gauging: Strain gauges are installed on tanks to measure the strain or deformation of the tank walls under various loads. This data helps in assessing the tank’s structural integrity and its ability to withstand operational stresses.
- Fitness-for-Service (FFS) Assessment: An FFS assessment involves a comprehensive evaluation of the tank’s condition to determine if it is fit for continued service. This assessment considers factors such as material degradation, structural integrity, and the intended use of the tank.
- Acoustic Leak Detection: This method uses sensitive microphones or accelerometers to detect the sound of leaks. It is particularly useful in buried tanks or those located in noisy environments where traditional leak detection methods might be less effective.