The frequency of tank inspections depends on several factors, including the type of tank, its usage, regulatory requirements, and the environment in which it is located. Tanks that store drinking water, hazardous chemicals, or fuel require more frequent inspections due to the potential risks associated with leaks or contamination. For water and wastewater tanks, there are several guidelines around inspection frequency, and most sources gravitate towards a three-year cycle. At Constructive, having seen how many issues can arise within a three-year window due simply to regular wear and tear. We advise staying on an annual schedule for detailed inspections performed by a tank specialist with additional periodic inspections conducted after major events in between annual inspections. The only exception to the annual frequency is for quick, routine inspections performed by operators. Here’s a general guideline on how often you should inspect your tank:
- Routine Visual Inspections: It is recommended that tanks undergo visual inspections on a monthly basis. These inspections are primarily to check for obvious signs of damage, such as corrosion, leaks, or structural deformities. These checks are normally quickly conducted by operators.
- External Inspections: An external inspection, which involves a more detailed examination of the tank’s exterior, should be conducted annually. This inspection includes checking the tank’s foundation, external coatings, insulation, and any external piping or fittings. External inspections may involve the use of non-destructive testing methods to assess the condition of the tank walls.
- Internal Inspections: Tanks that store drinking water or other critical substances should have internal inspections conducted annually to coincide with the external inspections to have a holistic assessment of the tank site and take advantage of mobilizations. Water tanks can be quickly inspected by underwater ROV. Wastewater tanks that can more easily be taken out of service should be taken out of service for inspection whenever possible.
- Cathodic Protection System Inspections: If your tank is equipped with a cathodic protection system to prevent corrosion, this system should be inspected annually. The inspection involves checking the system’s operation, measuring the electrical potential, and ensuring that the system is providing adequate protection to the tank.
- Leak Detection System Inspections: For tanks that have leak detection systems, these systems should be inspected and tested annually to ensure they are functioning correctly. This includes checking sensors, alarms, and any associated monitoring equipment.
- Settlement and Structural Inspections: Tanks that are large or located on unstable ground may require settlement and structural inspections as a part of the inspection checklist. These inspections assess the stability of the tank’s foundation and the overall structural integrity of the tank.
- Regulatory Inspections: Depending on the tank’s location and the type of substance it stores, regulatory agencies may require inspections on a specific schedule. For example, the Environmental Protection Agency (EPA) requires periodic inspections for underground storage tanks (USTs) that store hazardous substances which may be applicable to some wastewater facilities. These inspections are typically required every 1 to 3 years.
- Special Inspections After Major Events: Tanks should also be inspected after major events that could affect their integrity, such as earthquakes, severe storms, or significant operational incidents (like over-pressurization or chemical spills). These inspections help ensure that the tank has not been compromised and remains safe to operate. Other things to look for after severe weather events are signs of damage to collocated cell antennas which may pose a structural threat to the tank or a safety threat to people or structures at ground level.
- Aging Tanks: As tanks age, they may require more frequent inspections. Tanks over 20 years old should be inspected more frequently, particularly for signs of corrosion, material degradation, and structural weakening. In some cases, annual internal inspections may be necessary for older tanks. More frequent inspections, preventive maintenance, and proactive recoating can significantly prolong the tank life. Steel tanks that are properly maintained over time can see lifespans in excess of 100 years.
- Industry-Specific Guidelines: Certain industries may have specific guidelines for tank inspection frequency. For example, the American Water Works Association (AWWA) provides guidelines for the inspection of water storage tanks. Wastewater may have different criteria not mentioned specifically here. However, it’s worth noting that many industries have adapted or referenced the ASME BPVC for tank construction in their industry-specific guidelines. So when in-doubt the ASME BPVC provides helpful guidance for anything not explicitly mentioned in industry-specific literature such as the standards and manuals available from AWWA.
In summary, tank inspection frequency varies depending on the tank type, usage, and environmental factors. However, a general recommendation is to perform visual inspections monthly or quarterly, external inspections annually, and internal inspections every 3 to 5 years. Tanks in more demanding environments or those storing hazardous substances may require more frequent inspections.