Investigators are still trying to figure out what caused the natural gas pipeline rupture that shut down Interstate 95 and Florida’s Turnpike for several hours Monday morning.

Florida Gas Transmission, the Houston-based company that owns the 5,000-mile pipeline, sent three investigators to Martin County to examine the damage.

They probably will ship pieces of the broken 18-inch pipe for metal testing to help find clues, said company spokesman John Barnett. The segment of the pipeline that ruptured was built in 1959.

It’s unclear how long the investigation will take, Barnett said.