Definition
Double-Shoulder Connection — A double-shoulder connection is a rotary-shouldered thread with two torque shoulders — the standard external shoulder plus a secondary internal shoulder — that share make-up load to give higher torsional capacity and better fatigue resistance than single-shoulder API connections.
Also known as: double shoulder connection, double-shouldered connection, DS connection
How it works
A double-shoulder connection adds a second sealing/torque shoulder at the nose of the pin, inside the box, in addition to the conventional external shoulder found on API connections. When made up, both shoulders bear against the box, distributing the preload across two surfaces.
This second shoulder does two things: it acts as a positive torque stop that lets the connection be made up to a much higher torque before yielding, and it stiffens the connection to resist bending fatigue. Both benefits are why double-shoulder designs are standard on high-torque and extended-reach strings.
Advantages
- Torsional capacity — often 30% or more above the equivalent single-shoulder API connection.
- Fatigue life — the internal shoulder reduces stress at the last engaged thread.
- Compatibility — many double-shoulder connections are dimensionally interchangeable with a corresponding API connection but should be treated as their own type.
Renting double-shoulder tubulars
For high-torque directional and ERD wells, double-shoulder connections are frequently specified. We rent drill pipe and BHA components with double-shoulder connections — contact us to confirm your torque requirements.