NATCHEZ — Great River Industries builds big things.

But the Natchez-based tank and bulkhead manufacturing facility — which specializes in fabricated steel plate products, including storage tanks and pressure vessels for industrial process markets — has in recent months been fabricating something that’s been described as the biggest tank of its kind ever built.

Crews worked last week to ready a giant liquid natural gas tank that will eventually ship out of the Natchez-Adams County Port for a destination in the Caribbean.

“These tanks are the largest of their kind anywhere,” GRI Director of Operations Kevin Sullivan said. “They hold 255,000 gallons, and are 19 feet in diameter by roughly 180 feet long, and weigh in at around 450,000 pounds.”

When they’re installed in their final destination, the tanks can be used in gas the production field or at a refinery, Sullivan said.

From start to finish, the fabrication of such a tank takes between 24 and 30 weeks, and requires the construction of an inner and an outer tank.

The inner tank is composed of stainless steel, and measures 17 feet in diameter and 170 feet in length. It’s wrapped in high-grade special insulation to keep the inner tank at the temperature required for liquid natural gas storage.

The exterior tank is made of carbon steel.

The total tonnage is approximately 55 percent carbon steel and 45 percent stainless steel, Sullivan said.

“Once the inner tank was complete, you have to put that outer tank on in three steps. We’d put the center section on dollies, drive that onto the inner tank, and then you put the two end caps on — from there, it goes out, is painted and ready to go,” he said. “It’s a slow process that takes a lot of room.”

The engineering of the tanks was done by a company GRI had partnered with on the project.

“For this order, we had a partnership with another company that builds these tanks in bulk, but a lot smaller, and their plant couldn’t handle the size of the tank,” Sullivan said. “They did all the engineering, we did all the fabrication.”

Despite its large size, the tanks only require fewer than a couple of dozen workers to build them, Sullivan said.

“Our manpower for one of those tanks would peak out at about 20 guys,” he said. “Once you get it put together in big pieces, you can’t get many guys on — once it gets to a certain size, you can only have so many people working on it and be efficient.”

While the first tank has been completed, a second is nearing completion and two more are in the fabrication stages.

GRI acquired the former Enersteel’s Moran Road steel fabrication facility in July 2014, announcing that with the acquisition it would eventually locate its corporate headquarters from Memphis to Natchez.

Since GRI’s acquisition of the facility, several expansions have been made to accommodate new fabrication processes.

Prior to 2011, when Enersteel purchased the facility, the property was known as Dynasteel, and specialized in the production of duct work for the energy sector.

More information about GRI can be found online at greatriver360.com.