The National Transportation Safety Board allowed cameras inside the facility in Ashburn, Virginia today.
An expert says they will look at the metal composition and the source the explosion, which appears to be along the welding joint.
"See if there is any kind of corrosion, little weaknesses like a thinning of the wall thickness either due to an internal corrosion of an external corrosion," UCS Center On Megacities Director Jean-Pierre Bardet.
He says internal corrosion can be caused by some kind of liquid that collects and grows bacteria and external corrosion can be caused by soil.
He also says rocks and human activity can damage the protective coating around the pipe.
All of these things will be examined.
