Aboveground Storage Tanks (AST) are vital assets for many industries including, power, paper and pulp, oil and gas, chemical, and even beverage production. Routine inspection of external and internal tank components is beneficial for understanding its condition and is required by federal and local laws and regulations. Robot-enabled ultrasonic testing (UT) offers a unique solution to AST inspections because they save plant operators valuable resources while providing more asset coverage and actionable data.
In the United States, regulatory bodies established standards for the construction, inspection, maintenance, and relocation of AST to prevent leaks and spills that can be detrimental to the environment and the safety of plant employees and residents.
Understanding the existing regulations will help plant operators determine the best course of action for inspecting and repairing these valuable assets.
Regulations for Aboveground Storage Tanks
At the federal level, the U.S. Environmental Protection Agency (EPA) regulates certain AST that meet the requirements of the Spill Prevention Control and Countermeasure (SPCC) rule, a component of the department’s Oil Spill Prevention program. Initially established in 1973 under the Clean Water Act, the SPCC and Facility Response Plan (FRP) rules help plants with AST storing any type of oil – from petroleum to peanut – prepare for and prevent potential oil spills.
As defined in 40 CFR part 112, tanks and facilities that meet the criteria must adhere to SPCC, including the following:
- Aboveground oil storage capacity greater than 1,320 gallons in containers greater than 55 gallons, or a buried storage capacity of greater than 42,000 gallons; and
- Could reasonably discharge harmful amount of oil into U.S. waters or adjacent waterways, or effecting natural resources managed by the United States; and
- Is a non-transportation-related industry.
Apart from SPCC, state and local regulations and building and fire codes may also govern the construction, inspection, and maintenance of AST.
For many facility operators, it can be difficult to unpack the regulations to develop and implement an effective tank management program. Luckily, there are a couple of industry standards that are leading the way.
Industry Standards for Maintaining AST
The Steel Tank Institute (STI) and American Petroleum Institute (API) have established standards for aboveground storage tanks that assist operators in complying with EPA SPCC regulations.
STI SP001 was originally released in 2000 and is STI’s Standard for the Inspection of Aboveground Storage Tanks. This standard includes guidelines for the inspection of aboveground shop-built tanks under 75,000 gallons, small field-erected tanks, portable containers, and secondary containment. In recent iterations of the standard, inspection under STI SP001 takes a risk-based approach. In general, formal exterior and interior inspections must be completed by a certified STO SP001 inspector at five, ten, or twenty year intervals.
Alternatively, API 653 is API’s standard for the inspection, repair, alteration, and relocation of aboveground storage tanks constructed under API 650 (formerly API 12C), which encompasses the construction of riveted or welded field-erected steel tanks for oil storage. However, API 653 can also apply to any steel tank constructed to particular specifications. In addition, it provides guidance for the suitability of continued use and fitness-for-service, including recommendations for the maintenance of tank floor, shell, roof, nozzles, manways, and attached appurtenances.
The inspection guidelines set forth in API 653 are more stringent than STI SP001 because field-erected tanks have a higher environmental and safety risk if they leak or fail compared to shop-built tanks. An authorized API 653 inspector must complete formal inspections, with external inspections occurring at five-year intervals and internal inspections occurring every 10-30 years depending on risk-based criteria.
Depending on the scope of the tank, it could either fall under STI SP001, API 653, or both standards. If an AST falls under both, it is the operator’s responsibility to decide which set of standards the facility should comply with.
Regardless of the inspection approach, recent technological advancements in nondestructive testing (NDT) offer operators greater efficiency, objectivity, and accuracy to make data-driven AST management decisions.
Robotics Inspections for AST
Aboveground storage tanks are the backbone of facility operations and are currently the most prevalent large-scale asset class for the oil and gas, paper and pulp, and power industries. But, following STI SP001 or API 653 guidelines can be a daunting task for operators due to the size, scale, and complexity of inspections.
However, the recent introduction of robotic crawlers into NDT techniques provides operators with a comprehensive inspection program using the latest ultrasonic testing technology. Rapid Ultrasonic Gridding (RUG) and Rapid Automated Ultrasonic Testing (R-AUT), offer unparalleled safety, asset coverage, and data acquisition compared to visual, handheld, or drone inspection approaches.
Safety is a top priority for facility operators. Confined space entry (CSE) and elevated work requiring scaffolding and ropes all present potential hazards for inspection crews. Alternatively, deploying a robot to crawl tank floors, fixed roofs, and shells eliminates the need to put humans at risk - in addition to reducing extra expenses for scaffolding or other safety measures.
Industry leaders are pushing to make non-CSE inspections the standard. Dow Chemical is setting the bar for workplace safety by utilizing technology to complete dangerous work activities in an effort to eliminate workplace fatalities and serious injuries by 2025. One strategy for achieving their goal is to use robots and drones for CSE, elevated work, and industrial cleaning. In 2018 alone, Dow used robots in over 2,000 CSE and elevated work scenarios reducing the risk of injury and saving valuable resources.
When it comes to CSE scenarios, such as inspecting tank floors, robots are poised to handle the task. Equipped with up to 96 ultrasonic probes, robots can collect thousands of readings per ft2 to identify pits, corrosion, and general wear in the floor without the need for a human to enter the tank.
Understanding the overall condition of AST can be tedious and time-consuming without an NDT method that efficiently covers the entire asset. However, robots using RUG or R-AUT can cover unprecedented areas in a fraction of the time of conventional methods. Using RUG technology, robots can travel up to 60 ft/minute (18.3 m/minute) with a production rate of over 5,000 ft2 (467 m2) per 12-hour shift. R-AUT inspections pinpoint areas of concern at a production rate of up to 600 ft2 (56 m2) per shift. At these speeds, robots can easily reach nearly 100% asset coverage in one or two shifts.
Beyond safety and coverage, robotic inspections generate one thousand times more data than other inspection methods. Often software platforms are used to visualize the data as 2D or 3D C-scan heat maps. Inspectors and operators can use the readings and accompanying imagery to identify localized corrosion or other damage mechanisms present in the AST. Additionally, this information can be used for fitness-for-service calculations to determine corrosion rates.
RUG is best utilized for creating corrosion maps of tank shells and roofs. At as small as quarter-inch (6 mm) sensor spacing, each sensor takes up to 250 readings/foot (76.2 readings/meter). Then localized areas of concern can be further evaluated using R-AUT. While slower than RUG, R-AUT generates exponentially more data - over 94,000 readings per ft2 (28,600 readings per m2) to characterize damage mechanisms where it is needed the most.
Above all, and imperative for aboveground storage tanks, robotic inspections can be used to satisfy industry regulations, such as API 653. A full-service robotics company will have authorized API 653 inspectors on staff to inspect the asset using robots, and other methods as needed then will generate a comprehensive report to satisfy inspection criteria.
Conclusion
Aboveground storage tanks are regulated at the federal, local, and industry levels in order to prevent oil spills and other hazardous leaks and failures. Given the scale and complexity of AST inspections, robots utilizing the latest in UT technology offer a safe, reliable, and efficient alternative to conventional methods. Additionally, the data generated gives operators the confidence and ability to understand tank wear patterns and degradation to optimize the resources allocated for tank management.
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