Why ACS’s Marathon refinery upgrade leans on modular construction

Steel modules the size of small houses, shipped by barge and dropped into place in a working US refinery - ACS’s role in the Marathon Martinez Renewable Fuels upgrade shows how industrial construction is changing in practice.

Reviewed: ad hoc news Software & Services desk. Edited and checked on 2026-06-18, 11:58. Details in the imprint.

With the Marathon Martinez Renewable Fuels Project, ACS turns a conventional California oil refinery into a quieter landscape of steel modules, pipes and tanks tailored for renewable diesel and sustainable aviation fuel production. Cranes swing close over existing units, every move precisely choreographed.

What ACS is building in Martinez

The Marathon Martinez Renewable Fuels Project sits on the edge of the San Francisco Bay, where an older petroleum refinery is being converted to process biobased feedstocks into renewable diesel and sustainable aviation fuel. The work is taking place inside an active industrial site, with existing structures, tight pipe racks and constant safety constraints.

ACS, through its US engineering-construction arm, delivers large modular process units, pipe racks and supporting civil works that slot into this existing maze. Heavy-lift cranes position prefabricated modules that arrive by barge and truck, reducing on-site welding and time spent working at height in a noisy, constrained environment.

Why modular construction matters here

For investors and engineers alike, the interesting part is the modular strategy. Prefabricated units are assembled and tested in controlled yards, far from Bay Area fog and limited refinery work windows, then shipped to Martinez for final hook-up. This approach cuts weather downtime and allows parallel work streams instead of long sequential shutdowns.

From a cost and schedule perspective, modularization can compress critical-path durations in brownfield projects where every extra day of outage is expensive. Refinery staff feel the difference on the ground too: fewer open welds, less scaffolding, shorter periods when traffic routes and operating units are disrupted.

How the renewable fuels process changes the site

Technically, a renewable fuels plant still looks like a classic refinery skyline: columns, reactors, heat exchangers, tanks. But the feedstocks include used cooking oil, animal fats and other biobased oils, which are hydrotreated to produce cleaner fuels with lower life-cycle carbon intensity than conventional diesel and jet fuel.

That shift in feedstock means new tanks, upgraded piping systems and additional safety and odor-control equipment tailored to more variable, sometimes more corrosive input streams. Operators in Martinez now deal less with crude-tank odors and more with the sweeter, almost frying-oil notes that can drift across the site when feedstock deliveries are unloaded.

Working inside a live refinery

One of the sobering aspects of the Marathon Martinez Renewable Fuels Project is that much of the work happens with neighboring units still in service. That demands strict isolation, lockout procedures and intricate planning so that new tie-ins can be made during short pre-planned outages. Schedules are drawn almost like choreography, hour by hour.

Construction crews move through narrow corridors between operating pipes, often working at night or in carefully controlled day-shift windows to avoid interfering with ongoing operations. Radios crackle, spotters watch every lift, and even small tasks are wrapped in layers of permit checks, gas tests and coordination meetings.

What this means for ACS’s portfolio

For ACS, the Martinez renewable fuels conversion sits neatly alongside other energy-transition heavy projects, from LNG terminals to grid infrastructure upgrades. The company showcases its ability to handle complex brownfield sites where access is tight, schedules are unforgiving and community scrutiny around emissions and noise is intense.

Winning and executing projects like this strengthens ACS’s references in the US industrial market, where repeat work and safety performance are key selection criteria. The quiet, methodical work on modules and tie-ins today can translate into invitations to bid on similar conversions as more refineries explore renewable fuels or co-processing options.

Market context and stock reference

ACS Actividades de Construcción y Servicios, S.A., headquartered in Madrid, positions itself as a diversified infrastructure and industrial contractor with a growing footprint in North America. Shares of ACS Actividades de Construcción y Servicios, S.A. (ES0167050915) trade on Spanish exchanges, giving investors broad exposure to large-scale construction and concession projects.

Key facts on the Marathon Martinez project

• Product: Marathon Martinez Renewable Fuels Project
• Manufacturer: ACS Actividades de Construcción y Servicios, S.A.
• Category: Software/Service/Subscription (industrial project services)
• Launch: Conversion activities initiated in the early 2020s, with renewable fuels production ramping up mid-decade
• RRP / Price: Not disclosed at project level; multi-hundred-million-dollar industrial contract
• Availability: Industrial construction and project services for the Martinez site in California, ordered by Marathon and not a consumer product
• Target group: Energy companies seeking to convert or upgrade refineries to renewable fuels and lower-carbon processes
• Highlight / USP: Modular construction and complex brownfield execution in a live refinery environment

This article was AI-assisted and editorially reviewed. Product information without guarantee; prices and availability may change at short notice. No investment advice, no buy or sell recommendation. Stock-market transactions involve risks up to total loss.