Square Robot: Autonomous Tank Inspection Without Shutdown

Square Robot is a US-based robotics company that performs internal inspections of aboveground storage tanks using autonomous, submersible robots — without taking the tank out of service. Founded in 2016 and headquartered in Boston, Massachusetts, with operations in Houston, Texas, the company has completed more than 300 on-stream robotic tank inspections across four continents and secured Series B funding from Marathon Petroleum in December 2025. Its robotic platform delivers API 653 and EEMUA 159 compliant inspections while the tank remains in product and fully operational — eliminating the downtime, cleaning costs, confined space entry, and emissions release associated with conventional out-of-service inspections.

The Problem Square Robot Solves

Internal inspection of an aboveground storage tank under conventional methods requires taking the asset fully out of service: product removal, degassing, cleaning, personnel entry into the confined space, inspection, and refill. The process typically takes weeks to months and carries significant cost and risk. For a large crude or petroleum products tank, the combined cost of lost revenue, product removal, cleaning, and inspection can run into hundreds of thousands of dollars per event. API 653 mandates internal inspection on a risk-based interval — for many tanks, that means every five to ten years — making it a recurring operational burden for terminal operators and refiners.

Robotic tank inspections are conducted in days rather than the weeks and months required for traditional out-of-service inspections. Tanks remain in service throughout the on-stream inspection, negating the need for alternate storage, cleaning, purging, waste disposal, or manual inspection. For operators managing large tank farms, the ability to compress inspection timelines while keeping assets earning revenue changes the economics of tank integrity management materially.

The SR-1 and SR-3 Robot Platforms

Square Robot operates two submersible robot platforms in its commercial fleet. The original SR-1 was the company’s first-generation inspection robot, developed from 2016 and used to complete the company’s initial commercial inspections. The SR-3 is the current-generation platform, certified to NEC/CEC Class I Division 2 (C1D2) standard, with the SR-3 Side Launcher achieving the more stringent Class I Division 1 (C1D1) certification — both issued by FM Approvals in January 2025.

Square Robot field engineers use Factory Mutual C1D1 and C1D2 certified SR-1 and SR-3 submersible autonomous robots to inspect aboveground storage tanks in accordance with API 653 and EEMUA 159 requirements while tanks remain on-stream, in-service, and still containing low and high flashpoint products. The robots combine phased array ultrasonic testing (PAUT) with high-definition visual cameras. The PAUT array delivers 256-element phased array UT for volumetric wall loss measurements within 0.5 inches of tank walls and obstructions — covering the critical zone at the tank shell-bottom junction where corrosion failures most commonly initiate.

The SR-3 Side Launcher is a patented deployment system that allows robot launch and recovery through a side manway rather than a roof opening — enabling inspection of floating roof tanks containing volatile low-flashpoint products such as gasoline and jet fuel. The C1D1 certification for this environment, completed in partnership with ExxonMobil during an earlier joint development programme, was a significant expansion of the addressable market.

Data Output and API 653 Compliance

Each Square Robot inspection generates a high-density dataset used by a centralised team of senior inspectors to produce a compliance report. Unique high-resolution ultrasonic datasets provide unprecedented data density and tank bottom coverage, enabling clients to use more proactive, data-driven, risk-based inspection management systems. The data is also compatible with machine learning algorithms and AI to understand damage mechanisms and proactively manage them across tank fleets.

The inspection output supports API 653, API 575, EEMUA 159, risk-based inspection (RBI), and expected value analysis (EVA) frameworks — giving integrity engineers the data needed to set inspection intervals, plan maintenance, and satisfy regulatory requirements without the conventional confined space entry process. For operators running large portfolios of storage tanks — such as those profiled in the top tank equipment manufacturer rankings — data-driven integrity management at fleet scale is the primary commercial proposition.

Customers, Funding, and Commercial Expansion

In December 2025, Square Robot announced the completion of a Series B funding round and a strategic collaboration with Marathon Petroleum Corporation, which operates the largest refining system in the United States. Marathon will participate in the Series B round alongside other investors and collaborate to shape the development of Square Robot’s next-generation robotic platform, while continuing to deploy the existing fleet across its nationwide network of terminals and refineries. The Marathon partnership follows earlier backing from Crosstown Capital and confirmed deployments with ExxonMobil.

Square Robot has expanded commercially across four continents. In June 2025, Square Robot announced a strategic partnership with the Sutro Group to deliver robotic AST inspection services to clients across the United Kingdom. In March 2025, a separate agreement was announced with Institut de Soudure Industrie to deploy the technology in Belgium and France. These European partnerships extend Square Robot’s reach into markets where EEMUA 159 — the UK and European equivalent of API 653 — is the governing inspection standard. The Steel Tank Institute, which sets fabrication standards for US steel tanks, operates alongside API and EEMUA in defining the broader compliance framework within which Square Robot’s inspection data is deployed.

The Competitive Landscape

Square Robot operates in a growing segment of the inspection services market alongside other robotic tank inspection providers, including KOKS Robotics — which approaches the problem from a tank cleaning and no-man-entry angle — and traditional inspection contractors deploying rope access and conventional UT teams. The key differentiator for Square Robot is the on-stream capability: the ability to complete a full internal inspection without product removal or tank shutdown is a value proposition that conventional inspection methods cannot match.

The company’s goal, stated publicly, is to build a fleet of over 100 robots within the next five to ten years, compared to an initial fleet of 11 units. The Series B funding, the Marathon collaboration, and the European partnership agreements all reflect a business at commercial scale, moving from proving the technology to building the operational infrastructure for large-account deployment. For terminal operators evaluating aboveground storage tank service providers, Square Robot represents the most advanced available option for on-stream internal inspection across API and EEMUA jurisdictions.

Company Snapshot