HOUSTON, Jan 24 (Reuters) - Canada's Trans Mountain Corp will begin adding crude oil to its long-delayed pipeline expansion and expects it to be operating in the second quarter, an executive said on Wednesday.

The C$30.9-billion ($23.05 billion) expansion will nearly triple the flow of crude on Trans Mountain from Alberta to Canada's Pacific Coast but has been plagued by years of delays and cost overruns.

The start-up is expected in early April and will ramp up to full capacity by the end of the year, Jason Balasch, a senior director at Trans Mountain, said at the Argus Crude Summit in Houston.

The main challenge remaining with the expansion is installing a section of the pipeline through a mountain, which the company expects to complete early next week.

Canadian oil producers will ramp up output in the next couple of years and fill the expanded capacity, executives at the conference said.

Oil production will rise and deep discounts on Canadian crude ease as the pipeline comes online, said Jerry Miller, a senior vice president at U.S. oil refiner HF Sinclair.

U.S. refiners Delek US Holdings and Phillips 66 said they expect higher Canadian volumes to the West Coast to reduce prices there, offsetting some of the impact from higher prices in the U.S. mid-continent, which will see less Canadian crude flows once TMX is online.

"TMX has multiple knock-on effects in our organization," said Will Monteleone, president of Par Pacific Holdings , which processes Canadian crude oil at its refinery in Washington state. It also buys competing crude oil from Alaska and Latin America for a refinery in Hawaii.

Flows of Canadian crude oil to the U.S. Gulf Coast have been consistent and will not change with the expansion, pipeline operators Energy Transfer and Enterprise Products said. (Reporting by Arathy Somasekhar and Georgina McCartney in Houston; Editing by Alistair Bell)