Some 67 years after the Transco pipeline was laid from the Gulf Coast of Texas to New York City, it remains the crown jewel of the natural gas industry, fed by America’s richest shale patch. In the past year, the allure of this 10,500-mile system has helped trigger two failed takeover bids for Williams, a clash between Armstrong and billionaire pipeline magnate Kelcy Warren and a mass exodus from the company’s board.