Lockable connection between tubular members

1. A connection between a first tubular member and a second tubular member, the connection comprising:

a first tubular end including a first tubular end keyway;

a second tubular end;

a load shoulder member including a load shoulder member keyway and threadable onto the first tubular end;

a nut receivable around the first tubular end and the load shoulder member and threadable onto the second tubular end; and

wherein the load shoulder member is threadable onto the first tubular end until the load shoulder member keyway aligns with the first tubular end keyway to form an aligned keyway through the load shoulder member and into the first tubular end to receive a key member;

wherein the first tubular end is a pin end and the second tubular end is a box end to receive the pin end.

2. The connection of claim 1 wherein the nut is threadable onto the second tubular end over the load shoulder member and the first tubular end to capture the load shoulder member between the nut and the second tubular end.

3. The connection of claim 1 further comprising a first threaded interface between the load shoulder member and the first tubular end, and a second threaded interface between the nut and the second tubular end, wherein the aligned keyway intersects the first threaded interface.

4. The connection of claim 3 wherein the connection lacks a threaded interface formed directly between the first tubular end and the second tubular end.

5. The connection of claim 1 further comprising a second tubular end recess to receive a load shoulder member protrusion.

6. The connection of claim 1 further comprising a plunger extending through the nut and into the first tubular end.

7. The connection of claim 1 wherein the box end includes external threads and lacks internal threads.

8. The connection of claim 1 wherein the box end is configured to receive the pin end at a slidingly-engageable, rotatable interface.

9. A method of connecting two aligned tubular members, the method comprising:

sliding a nut over a first tubular pin end;

threading a load shoulder member onto the first tubular pin end until a load shoulder member keyway aligns with a first tubular pin end keyway;

inserting a key member into the aligned load shoulder member and first tubular pin end keyways;

engaging the first tubular pin end with a second tubular box end such that a second tubular box end recess receives a load shoulder member protrusion; and

threading the nut onto the second tubular box end.

10. The method of claim 9 further comprising disposing a pin in the nut and in the first tubular pin end after threading the nut onto the second tubular box end.

11. A connection between tubular members, comprising:

a first tubular member having a first tubular end with a first externally threaded region and a seal region along an outer surface;

a second tubular member having a second tubular end with a second externally threaded region and a counter bore configured to slidingly receive the seal region;

a load shoulder member threadable onto the first externally threaded region to form a first threaded interface; and

a nut receivable around the outer surface of the first tubular end and threadable onto the second externally threaded region to form a second threaded interface;

wherein the load shoulder member and the second tubular end are engageable to form a castellated interface;

wherein the first tubular end is a pin end and the second tubular end is a box end to receive the pin end.

12. The connection of claim 11 further comprising a keyway through the load shoulder member and into the first tubular end to receive a key member.

13. The connection of claim 11 wherein the connection lacks an interface configured to transfer torque directly between the first tubular end and the second tubular end.

14. The connection of claim 13 wherein the connection lacks an interface configured to transfer an axial load directly between the first tubular end and the second tubular end.

15. The connection of claim 11 wherein the load shoulder member is positioned within a volume defined by the first tubular end, the second tubular end, and the nut when the connection is assembled.

16. The connection of claim 15 wherein the load shoulder member is surrounded by the first tubular end, the second tubular end, and the nut when the connection is assembled.

17. The connection of claim 11 further comprising a rotation-inhibiting interface formed between the nut and the first tubular end.

18. The connection of claim 11 wherein the load shoulder member comprises a shoulder configured to engage the second tubular end at a shoulder interface and at the castellated interface, and wherein when the connection is made-up, the shoulder interface is tightened axially, and the castellated interface is not tightened axially.

19. The connection of claim 11 wherein the load shoulder member is configured with a first shoulder to form a first shoulder interface with the nut and a second shoulder to form a second shoulder interface with the second tubular end;

wherein the first or second threaded interface includes straight, Acme threads; and

wherein, when the connection is made-up, the first and second shoulder interfaces are tightened axially to transfer an axial load.