South Carolina Electric & Gas started doing more business with Dominion Energy this week, and for once, it had nothing to do with their plans to combine.

Instead, this line of business was in the works for years, long before the failure of SCE&G's nuclear project put the power company on the auction block.

Building a new gas pipeline is no quick task, after all.

Dominion says natural gas is now flowing through running a new expansion of its pipeline network in South Carolina, giving it the capacity to shuttle more of the fuel from the Upstate across the state. The so-called "Charleston project" was fired up Thursday morning.

As part of the project, Dominion installed 55 miles of pipe from an existing major gas connection near Spartanburg to the Midlands. It also installed a handful of new compressors that will push more gas through its network.

The $125 million expansion is among the most expensive gas projects in state history, Dominion says, and it has the capacity to push 80,000 dekatherms of gas through the state. That's enough to warm tens of thousands of homes on a winter day. It could also take 100 Olympic swimming pools from room temperature to a boil.

All but a small fraction of the new capacity is earmarked for SCE&G. The utility says it will use about a third of its extra space to run gas-fired power plants, like Williams Station in Goose Creek.

The rest will be resold to factories and homes, where gas is used often used for cooking and heat. SCE&G spokesman Eric Boomhower says the utility decided to buy more capacity to keep up with an expanding customer base.

SCE&G has been adding gas customers at a roughly 3 percent clip in recent years, though securities disclosures show that sales volume is growing at a more modest pace.

Dominion spokesman Frank Mack says that more than a third of the extra capacity is slated for delivery in the Lowcountry. The company built a compressor station in Dorchester County that will pack more gas into the southern end of its network.

The project also gives South Carolina more access to the huge Transco pipeline, a major artery that runs from the Gulf of Mexico to the Northeast. Gas production has exploded at its northern end, where fracking technology has set off a boom in exploration.

Dominion, a Virginia-based utility giant, bought its network in South Carolina three years ago from SCE&G's parent company, Cayce-based SCANA Corp. But the companies' ties have deepened since.

Dominion agreed to buy SCANA earlier this year in a deal valued at $14.6 billion. Dominion's advances began last spring, but SCANA warded them off until the end of 2017. SCANA eventually warmed to the idea of a sale as the firestorm over its nuclear project began to burn uncontrollably.

The uproar surrounding the failed expansion of the V.C. Summer nuclear plant also means that the Dominion deal might not go through: Regulators and the Legislature need to give the acquisition their blessing before it closes.

Reach Thad Moore at 843-937-5703. Follow him on Twitter @thadmoore.