Out in the Oil Field: Tank Coating

STORAGE TANKS · PROTECTIVE COATINGS · SURFACE PREPARATION · OIL & GAS

A successful tank-lining project depends on more than choosing the right coating. Access, surface preparation, steel condition, temperature, humidity, safety, application equipment, and return-to-service requirements all have to work together.

That combination of challenges came together when NTS, Inc. coated the interior of a large heavy-crude storage tank at the Elk Hills oil field in California. The project involved a tight schedule, winter weather, high-temperature service, extensive surface preparation, and the added safety demands of working inside an operating oil field.

A 40,000-Barrel Heavy Crude Storage Tank

The tank was located at the Elk Hills oil field in California’s southern San Joaquin Valley. According to the original case study, NTS regularly performed work at the site.

This particular tank stored heavy crude oil and had a reported capacity of approximately 40,000 barrels. It measured roughly 100 feet in diameter and 32 feet high.

An eight-person NTS coatings crew was responsible for abrasive blasting and coating application inside the tank.

Creating Better Access to the Tank Interior

The tank originally had two 36-inch manholes for access. To make movement of personnel, equipment, abrasive, and materials more practical, a larger door sheet was temporarily cut from the tank shell.

After the project was complete, the door sheet was welded back into place and the affected steel was coated as part of the lining system.

Removing the Existing Epoxy Lining

Before the new lining could be installed, the crew had to remove the existing epoxy coating and prepare the carbon steel substrate.

The project used abrasive blasting supported by an eight-ton blast pot, dust collection, dehumidification, and compressed-air drying equipment.

According to the case study, the interior was abrasive blasted twice to what was then designated NACE No. 1/SSPC-SP 5, White Metal Blast Cleaning. A chloride wash was performed between the blasting operations to help remove soluble salts.

Surface Preparation Revealed Steel That Needed Repair

Coating replacement projects often uncover substrate conditions that were not fully visible before the existing lining was removed.

During this project, welding repairs were made where necessary on the tank shell and roof. In areas where deterioration was severe, steel plate sections were replaced.

Those repairs had to be completed before the lining system could be applied over a sound, properly prepared substrate.

Winter Weather Complicated the Application

Environmental control was necessary to keep the interior within acceptable coating-application conditions during winter weather.

The project took place during winter, when temperatures in California’s San Joaquin Valley could fall below the coating system’s minimum application temperature.

The source reports that the coating used on the project required application temperatures of at least 50°F (10°C), and humidity also needed to remain controlled.

The crew therefore used heaters and dehumidifiers to maintain suitable ambient conditions inside the tank.

The Finished Lining Had to Survive Much More Heat

Ironically, while the crew had to heat the tank to apply the coating in winter, the lining itself had to tolerate much higher service temperatures once the tank returned to operation.

The heavy crude oil was reportedly stored at approximately 225–250°F (107–121°C) to help maintain movement and handling characteristics.

The historical project selected Sherwin-Williams Nova-Plate 325, described in the original case study as a ceramic- and glass-flake-filled novolac epoxy suitable for high-temperature immersion service.

Why a Novolac Epoxy Was Selected

Novolac epoxies are highly cross-linked coating materials commonly used where elevated temperature and chemical resistance are important.

In the original project, the selected lining was intended to resist the combination of hot crude service, process chemicals, produced-water exposure, and abrasion associated with upstream production.

The specific coating system also offered scheduling advantages that supported the project’s tight turnaround.

Stripe Coating the Difficult Areas

Tank interiors contain welds, edges, angles, crevices, attachments, and other geometries where achieving uniform coating thickness can be more difficult than on broad flat surfaces.

The project’s reported recoat window allowed the crew to apply stripe coating around these details without requiring a different material or an additional full surface-preparation cycle.

Applying the Tank Lining

The crew applied the lining using a Graco 70:1 XM plural-component spray system.

According to the historical case study, one coat was applied throughout the tank interior at a specified dry film thickness of approximately 20–30 mils (508–762 μm).

For a high-build plural-component system, correct proportioning, mixing, spray technique, environmental control, film-thickness verification, and equipment operation are all critical to achieving the intended lining performance.

Working Inside an Operating Oil Field Raised the Stakes

Perhaps the most demanding part of the project was not the coating itself but the environment surrounding the work.

The tank was located in a fully operational oil field, so the crew continuously monitored for hydrogen sulfide and combustible-gas conditions during the job.

The historical article also describes flame-resistant clothing, hard hats, safety glasses, protective footwear, respiratory protection during coating application, and Type CE abrasive-blast respirators during blasting.

Why Schedule-Friendly Coating Properties Mattered

Storage tanks are productive assets. Every additional day out of service can affect operations, which makes turnaround planning a major part of many lining projects.

The original project emphasized two characteristics of the selected coating system that helped the schedule: a reported 24-hour return-to-service time and a 14-day recoat window.

Those characteristics gave the crew flexibility to complete detail work and reduce the time between final application and tank turnover.

Successful tank-lining work depends on coordinating substrate repair, surface preparation, environmental control, application, inspection, safety, and return-to-service requirements.

The Bigger Lesson: Tank Lining Is a System

It would be easy to describe this project simply as the application of a high-temperature epoxy lining. The actual work was much broader.

The crew had to create access, remove an existing coating, control dust, manage soluble salts, identify damaged steel, coordinate welding and plate replacement, maintain environmental conditions, stripe-coat details, operate plural-component spray equipment, monitor hazardous atmospheres, and return the tank to service within the required schedule.

The lining material mattered, but its success depended on every one of those supporting activities.