Improper drainage of steam lines could cause:

Improper drainage of steam lines can lead to water accumulation within the pipes, which can cause water hammer. Water hammer is a phenomenon where the sudden change in momentum of the steam traveling through the line collides with the trapped water, creating shock waves that can lead to loud banging noises and potential damage to the piping system. This situation not only risks the structural integrity of the steam lines but can also cause issues such as pipe deformation, fittings loosening, and even rupturing.

Other potential consequences mentioned in the other choices, like excessive weight to the pipe, low pressure in the lines, and excessive steam pressures, do not have the same direct impact as water hammer. While these scenarios can occur under certain conditions, they are not primarily caused by inadequate drainage, making water hammer the most immediate and significant concern related to steam line maintenance and operations.