Rotating continuous flow sub

1. A method for drilling a wellbore, comprising:

drilling the wellbore by advancing a tubular string longitudinally into the wellbore;

stopping drilling by holding the tubular string longitudinally stationary;

adding a tubular joint or stand of joints to the tubular string while injecting drilling fluid into a side port of the tubular string, rotating the tubular string, and holding the tubular string longitudinally stationary;

resuming drilling of the wellbore after adding the joint or stand;

opening the port before injecting drilling fluid into the port;

stopping injection of drilling fluid into the port after adding the joint or stand;

closing the port after stopping injection of drilling fluid into the port;

engaging the tubular string with a clamp before opening the port; and

disengaging the clamp from the tubular string after closing the port,

wherein:

the port is opened and closed by operating an electric, pneumatic, or hydraulic actuator,

the actuator is part of the tubular string, and

the clamp provides electrical, hydraulic, or pneumatic power to the actuator.

2. The method of claim 1 , wherein the actuator opens and closes the port by longitudinally moving an internal sleeve of the tubular string to expose and cover the port.

3. A method for drilling a wellbore, comprising:

drilling the wellbore by advancing a tubular string longitudinally into the wellbore;

stopping drilling by holding the tubular string longitudinally stationary;

adding a tubular joint or stand of joints to the tubular string while injecting drilling fluid into a side port of the tubular string, rotating the tubular string, and holding the tubular string longitudinally stationary;

resuming drilling of the wellbore after adding the joint or stand;

opening the port before injecting drilling fluid into the port;

stopping injection of drilling fluid into the port after adding the joint or stand;

closing the port after stopping injection of drilling fluid into the port;

engaging the tubular string with a clamp before opening the port; and

disengaging the clamp from the tubular string after closing the port,

wherein the port is opened and closed by an internal sleeve of the tubular string longitudinally moving in response to injection and stoppage of injection of drilling fluid into the port to expose and cover the port.

4. A method for drilling a wellbore, comprising:

a) while injecting drilling fluid into a top of a tubular string disposed in the wellbore and having a drill bit disposed on a bottom thereof and rotating the tubular string:

drilling the wellbore by advancing the tubular string longitudinally into the wellbore; and

stopping drilling by holding the tubular string longitudinally stationary;

b) injecting drilling fluid into a side port of the tubular string while injecting drilling fluid into the top, rotating the tubular string, and holding the tubular string longitudinally stationary;

c) while injecting drilling fluid into the port, rotating the tubular string, and holding the tubular string longitudinally stationary:

stopping injection of drilling fluid into the top;

adding a tubular joint or stand of joints to the tubular string; and

injecting drilling fluid into the top; and

d) stopping injection of drilling fluid into the port while injecting drilling fluid into the top, rotating the tubular string, and holding the tubular string longitudinally stationary.

5. The method of claim 4 , further comprising:

opening the port before injecting drilling fluid into the port; and

closing the port after stopping injection of drilling fluid into the port.

6. The method of claim 5 , further comprising:

engaging the tubular string with a clamp before opening the port; and

disengaging the clamp from the tubular string after closing the port.

7. The method of claim 6 , wherein the port is opened and closed by operating an electric, pneumatic, or hydraulic actuator.

8. The method of claim 7 , wherein:

the actuator is part of the tubular string, and

the clamp provides electrical, hydraulic, or pneumatic power to the actuator.

9. The method of claim 8 , wherein the actuator opens and closes the port by longitudinally moving an internal sleeve of the tubular string to expose and cover the port.

10. The method of claim 7 , wherein:

the actuator is integral with the clamp, and

the actuator opens and closes the port by removing and installing a plug from and into the port.

11. The method of claim 10 , wherein:

the tubular string comprises a swivel, and

the port is formed through a wall of the swivel.

12. The method of claim 10 , wherein the port is formed through a wall of a joint of the tubular string.

13. The method of claim 12 , wherein:

the tubular string comprises a swivel, and

the clamp engages the swivel.

14. The method of claim 12 , wherein:

the clamp comprises a swivel, and

the swivel engages the tubular string.

15. The method of claim 6 , wherein the port is opened and closed by an internal sleeve of the tubular string longitudinally moving in response to injection and stoppage of injection of drilling fluid into the port to expose and cover the port.

16. The method of claim 4 , wherein:

drilling is further stopped by substantially reducing an angular velocity of the drill string, and

rotation of the tubular string adding the joint or stand is at the substantially reduced angular velocity.

17. The method of claim 4 , wherein:

the wellbore is drilled using a top drive, and

the tubular string is rotated while adding the joint or stand using a rotary table.

18. The method of claim 4 , further comprising:

closing a portion of a bore of the tubular string between the port and a top of the tubular string before adding the joint or stand; and

opening the bore portion after adding the joint or stand.

19. The method of claim 4 , wherein a float valve of the tubular string closes a portion of a bore of the tubular string during adding of the joint or stand.

20. The method of claim 4 , further comprising stopping rotation of the tubular string before adding the joint or stand.

21. The method of claim 4 , wherein rotation of the tubular string is continuously maintained during the method.

22. The method of claim 4 , wherein the port is located downhole or subsea while the joint or stand is added.