The U.S. shale oil revolution can't be stopped, but it could be delayed by a potential shortfall of 10-ton valves and giant pipeline pumps essential for rebalancing markets upended by the surge in production.

Amid an unanticipated boom in inland oil output that turned the domestic market upside down last year, firms from Enterprise Products Partners to Shell Pipeline and Plains All American have launched a $20 billion bonanza to build, expand or reverse two dozen pipelines in the past year.

But as they help effectively to switch the flow of oil from the north to southern refineries and relieve the glut of cut-price, landlocked crude, concerns are growing that the firms that make key pipeline components may be straining to keep pace.

"The supply chain hasn't quite caught up," said Terry McGill, president of Enbridge Energy Co Inc, the U.S. division of Canadian pipeline giant Enbridge Inc, which has some $4 billion worth of U.S. projects on the books.

Thus far, there are no signs of project delays or cost overruns in what is the biggest build-out of oil and liquid pipelines since World War II.

Executives say they are building in plenty of lead time to produce dozens of multi-ton valves and massive pumps essential for maintaining pipeline flow. Underutilized steel mills, meanwhile, can rev up furnaces to forge the pipes -- which have a diameter of up to 42 inches.

But the task is enormous. After decades of moving U.S. offshore or Middle East crude from the Gulf Coast to inland refineries, pipelines must flow in the opposite direction to accommodate surging output from Canada and shale oilfields such as North Dakota's Bakken.

It all makes for a historic boom, said Larry Schwartz, senior analyst for natural gas liquids at consultancy Wood Mackenzie: "Midstream, which was the redheaded stepchild, is now in vogue."