U.S. regulators have barred TransCanada Corp. from restarting its Keystone pipeline until the company can provide more proof that the system is safe, after several leaks in just a year of operation..... 

 Following at least three Keystone leaks in May, the U.S. Pipeline and Hazardous Materials Safety Administration took sudden action Friday. It issued a corrective action order that mandates 14 steps TransCanada must take before resuming operations, including demands for information, mechanical and metallurgical testing and a report on all issues and incidents on the line.... 

 For Canada's oil and gas industry, the Keystone outage is just the latest in a series of pipeline-related headaches. A major Michigan spill on an Enbridge Inc. pipeline last summer resulted in rolling outages that lasted until this spring, as the company worked to fix problems on the line