As the connection is made-up from the handtight to power-tight position, the box counterbore compresses, the pin base elongates elastically and the internal secondary torque shoulder engages. The secondary torque shoulder allows for enhanced load distribution across the threaded region and provides increased torsional capacity when compared to standard API rotary shouldered connections.

Since the secondary shoulder functions solely as a torque stop and not a pressure seal, minor damage to the shoulder can be tolerated without adversely affecting connection performance.

• Enhanced torque capacity compared to API
• More OD wear before downgrading
• Interchangeable with API
• Improved hydraulic efficiency
• Flush ID connection

IMPROVED Torque CAPACITY
GPDS connections offer significantly higher torsional capacity than standard API connections of similar size. The additional strength provides the required torque for drilling to extended depths or in more performance-demanding environments. GPD S connections provide 20% to 50% greater torque when compared to API connections of the same dimensions. As a result, GPD S tool joints can support larger ID s than assemblies with API connections, improving hydraulic efficiency without sacrificing available connection torsional strength or wear allowance.

EXTENDED Wear ALLOWANCE
Because of its increased torsional capacity, the GPD S connection greatly extends the life of the joint by tolerating more OD wear. For example, an NC 50 connection on 5 inch 19.50 lb/ft S-135 drill pipe is downgraded to API Class 2 when the OD wears below 6-5/16 inches. At this diameter, the tool joint is less than 80% as strong as API Premium Class pipe. The GPD S50 double shoulder connection can tolerate wear down to a diameter of 5-15/16 inches, resulting in a 123% improvement in tool joint wear allowance.

Interchangeability
NOV Grant Prideco's GPDS connection is similar to API connections, except that the GPD S incorporates an internal secondary torque shoulder. The GPD S connection has the same thread form and is interchangeable with its API counterpart connection as shown in the illustration above. Note how the GPD S pin secondary torque shoulder runs out without shouldering in the back of the API box connection.

"Interchangeability" means that the connections will mate together, make-up and function; however, the performance properties will be limited to that of the API connection. For example, a GPD S38 is interchangeable with NC 38, and a GPD S55 is interchangeable with the 5-1/2 FH, but when mated together the NC and FH limit the connection performance properties respectively. The table to the right identifies the GPD S connections and their interchangeable API connection types.

Slim Profile
The GPDS connection's increased torsional strength allows for tool joint dimensional optimization more suitable for the pipe body torsional strength. GPD S connections can be configured with a smaller OD and larger ID compared to standard API connections without sacrificing torsional capacity. This feature allows a larger diameter drill pipe to be used for improved hydraulic performance. The GPD S double-shoulder design also provides a true flush inside diameter through the mated tool joint assembly. There is no gap or change in the inside diameter from the box to the pin, creating a smoother fluid flow with less turbulence, in addition to eliminating the opportunity for trapped cement and cuttings.