The round mandrel slip joint, like other slip joints, accepts the movement associated with ocean heave or temperature change without allowing the movement to disturb the placement of downhole tools.

The round mandrel slip joint has the following characteristics:

? Top of the mandrel slip joint has4 3/4-in. (120.65-mm) drill collar profile for easy handling with the rig elevators and slips

? Maintains its full tensile rating when collapsed and locked

? Can be locked in the closed position for handling, reducing the risk of damage to the lifting/sealing mandrel

? Internally pressure and volume balanced

? String can be picked up with the slip joint locked; the slip joint can then be unlocked before it is run into the hole

? Provides free travel in the string to reciprocate tools without unseating the packer

A slip joint operates by balancing its volume. As the slip joint stretches and increases its internal volume, a differential piston within the slip joint allows the same volume of fluid into the pipe. The net result is no change in internal volume.

Each slip joint has 5 ft (1.52 m) of travel but can be combined with other slip joints to provide additional travel.

When multiple slip joints are run, they are normally connected to one another rather than located throughout the pipe string. The number of slip joints required depends on ocean heave and the amount of expected contraction and expansion.