There are no Metro station closings this weekend, but crews will be working on four lines. (Robert Thomson - Washington Post) (Robert Thomson/The Washington Post)

Metro said a small piece of equipment, called a tie crane, derailed at a slow speed early Friday morning near the Brentwood-Rhode Island Avenue station on the Red Line.

The equipment is used to install ties on the tracks. It was en route at a speed of less than 16 mph, Metro said, to do work in the area of the No-Ma-Gallaudet U and Union stations when it derailed.

The cause is under investigation and there were no injuries. The equipment was back on the tracks and working in roughly 20 minutes.

Dan stessel, a Metro spokesman, said the incident was not related to last week’s derailment, which was near the Rhode Island Avenue stop and was on the outbound track. Friday’s incident was on the inbound track but in the same general area.

A person nearby called the fire department and said they thought they heard an explosion. Metro said the sound was caused by an arcing insulator on the track.

Watch a video of a tie crane at work: