The Power of 3D Laser Scanning in Tank Inspections: From Underground to Above-Ground Storage Tank Applications

As industrial infrastructure continues to age, ensuring the safety and reliability of critical assets like storage tanks has become a top priority. 3D laser scanning tank inspections have emerged as a powerful solution where traditional methods often fall short in precision, efficiency, and safety. By capturing millions of data points and creating highly accurate digital models, this technology allows engineers to analyze structures in ways that were previously impossible. This article presents technical data and discussion on underground fiberglass storage vessels and aboveground steel storage tanks as examples.

3D Laser Scanning of Underground Fiberglass Reinforced Plastic Tanks

Underground storage tanks are commonly constructed in accordance with UL 1316 [1], the standard for Fiber Reinforced Underground Tanks used to store flammable and combustible liquids. UL 1316 serves as the primary guideline for the design and performance of fiberglass-reinforced plastic (FRP) underground storage tanks. It applies to single-wall, double-wall, and triple-wall configurations intended for non-pressurized, fully buried installations, commonly used for storing products such as gasoline, diesel, fuel oil, alcohols, and approved fuel blends.

This standard outlines the minimum requirements for materials, design, and structural performance, including specifications for resin systems, fiberglass reinforcement, corrosion protection, wall thickness, fittings, and manufacturing quality control. It also establishes rigorous testing criteria to ensure tanks can withstand burial conditions, including soil and traffic loads, groundwater pressure, hydrostatic forces, temperature variations, and long-term corrosion exposure. Tanks that comply with UL 1316 must be properly labeled to indicate their certification and compatibility with specific stored substances.

3D laser scanning of underground fiberglass reinforced plastic tanks is used to survey diameter compliance, compression/expansion of horizontal and vertical axes, and roundness. The data may be used to confirm that the tank was fabricated to specification and/or to confirm that the tank was installed correctly. A typical slice of a 3-D laser scan for roundness is shown in Figure 1. The data presents the reference diameter, measured diameter and tolerance – sometimes 1%. The average roundness deviation may be calculated over the length of the tank.

Figure 1:  3D laser scanning roundness data from on an underground fiberglass reinforced tank showing reference diameter, measured diameter and tolerance.

3D Laser Scanning of Aboveground Storage Tanks, Pressure Vessels, and Piping

3D laser scanning also plays a key role in quality control and compliance with industry standards, particularly those established by the American Petroleum Institute (API). Among these, API-653, API-510, and API-570 are especially important.

• API-653 focuses on the inspection, repair, and maintenance of above-ground storage tanks. In the above-ground tank report, API-653 was used to evaluate roundness, plumbness (vertical alignment), and shell settlement. For example, the tank exceeded roundness tolerances in certain areas, while its settlement remained within allowable limits. 3D laser scanning enhances API-653 inspections by providing highly accurate geometric data that supports these evaluations.

• API-510 applies to pressure vessels, focusing on their structural integrity and safe operation. While the reports primarily involve storage tanks rather than pressure vessels, the same scanning principles can be applied. For example, 3D laser scanning can detect deformation, bulging, or misalignment in pressure vessels, helping inspectors ensure compliance with API-510 requirements.

• API-570 governs the inspection and maintenance of piping systems. Although piping is not the primary focus of these reports, 3D laser scanning can also be used to assess pipe alignment, detect sagging or displacement, and verify installation accuracy. This makes it a valuable tool for supporting API-570 inspections, especially in complex industrial facilities where piping networks are extensive.

One of the most important uses of 3D laser scanning is detecting structural deformation. In both cases, engineers used scanning to evaluate the roundness of cylindrical tanks, a critical factor in maintaining structural integrity. Over time, tanks can warp or deform due to pressure, environmental conditions, or foundation shifts. Roundness tolerances per API 653 can be summarized as follows:

Radii measured at a point 1 foot above the shell-to-bottom weld must remain within the allowable limits specified in Table 10.2. For measurements taken above this 1-foot elevation, the permitted deviation increases to three times the values listed in the table.

Table 10.2 defines acceptable radius tolerances based on tank diameter:

• For tanks less than 40 ft in diameter: ±0.5 in

• For tanks from 40 ft to less than 150 ft: ±0.75 in

• For tanks from 150 ft to less than 250 ft: ±1.0 in

• For tanks greater than 250 ft: ±1.25 in

These tolerances establish the allowable variation from a true circular shape, with greater flexibility permitted at higher elevations along the shell.

The maximum allowable deviation from vertical alignment at the top of the tank shell, relative to the base, must not exceed 1/100 of the total tank height, with an absolute limit of 5 inches. This same requirement also applies to fixed roof support columns. For tanks equipped with internal floating roofs, the applicable criteria should be taken as the most restrictive between this requirement and those outlined in API 650 Section 7.5.2 and Section H.4.1.1.

Additionally, the vertical deviation within any single shell course must remain within the allowable mill tolerances specified in either ASTM A6 or ASTM A20, depending on which standard applies.

Figure 2:  Example aboveground storage tank roundness 3D laser mapping of roundness mapped by circumferential location, tank height, and color coded from dark to light for negative and positive tolerances.

Figure 3:  Example aboveground storage tank roundness 3D laser mapping of plumbness mapped by circumferential location, tank height, and color coded from dark to light for negative and positive tolerances.

Another important application is monitoring structural performance over time. Because 3D laser scans create a permanent digital record, they allow for easy comparison between inspections. Engineers can track changes in deformation, settlement, or alignment, making it possible to identify gradual deterioration before it leads to failure. In the above-ground tank report, certain areas were recommended for continued monitoring, demonstrating how scanning supports long-term asset management.

Finally, 3D laser scanning significantly improves safety and efficiency, especially in challenging environments. Underground tanks are confined spaces that can be hazardous to inspect manually, while large above-ground tanks require extensive time and effort using traditional methods. Laser scanning minimizes the need for prolonged physical access, allowing technicians to collect comprehensive data quickly and safely.

Conclusion

Together, these two inspections illustrate the full potential of 3D laser scanning across different types of infrastructure. Whether applied to underground or above-ground tanks, the technology provides unmatched accuracy, detailed visualization, and reliable data for decision-making. From detecting deformation and verifying compliance to improving safety and enabling long-term monitoring, 3D laser scanning is transforming how engineers approach inspection and maintenance. As industries continue to prioritize efficiency and risk reduction, this technology will only become more essential in safeguarding critical assets.

References

1. American Petroleum Institute (API). API Standard 653: Tank Inspection, Repair, Alteration, and Reconstruction. Latest Edition.

2. American Petroleum Institute (API). API Standard 650: Welded Steel Tanks for Oil Storage. Latest Edition.

3. American Petroleum Institute (API). API Standard 510: Pressure Vessel Inspection Code: In-Service Inspection, Rating, Repair, and Alteration. Latest Edition.

4. American Petroleum Institute (API). API Standard 570: Piping Inspection Code: In-Service Inspection, Rating, Repair, and Alteration of Piping Systems. Latest Edition.

5. UL Solutions. UL 1316: Standard for Safety – Glass-Fiber-Reinforced Plastic Underground Storage Tanks for Petroleum Products, Alcohols, and Alcohol-Gasoline Mixtures.

6. ASTM International. ASTM A6/A6M: Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes, and Sheet Piling.

7. ASTM International. ASTM A20/A20M: Standard Specification for General Requirements for Steel Plates for Pressure Vessels.

8. ASTM International. ASTM E2807: Standard Specification for 3D Imaging Data Exchange (E57 File Format).

9. ASTM International. ASTM E57 Committee on 3D Imaging Systems – Standards for Performance Evaluation and Terminology.