WASHINGTON  Internal documents from BP show that there were serious problems and safety concerns with the Deepwater Horizon rig far earlier than those the company described to Congress last week.

The problems involved the well casing and the blowout preventer, which are considered critical pieces in the chain of events that led to the disaster on the rig.

The documents show that in March, after several weeks of problems on the rig, BP was struggling with a loss of “well control.” And as far back as 11 months ago, it was concerned about the well casing and the blowout preventer.

On June 22, for example, BP engineers expressed concerns that the metal casing the company wanted to use might collapse under high pressure.