Why do I need/want a Double Shoulder Connection on my Drill String?

Since their introduction in the 1980’s, double shoulder connections (DSC’s) have evolved significantly in response to the drilling industry’s increasing demands for deeper drilling.

When it comes to more advanced drilling programs, choosing the right connection for your drill string is a big deal! People often wonder, what makes a DSC better than the standard API Rotary Shoulder Connection (RSC). The simple answer: the DSC gives you more torsional strength due to its secondary shoulder engagement.

Picking a DSC from our extensive library of connections does not just mean more torque—between 25% to a whopping 85% more than an API RSC. There is more to it than just an increase in torque. DSC’s provide configurations with smaller OD’s and larger ID’s, making them ideal for slim hole drilling while simultaneously improving hydraulic efficiency. Additionally, DSC’s have demonstrated superior fatigue resistance when compared to similarly sized API RSC’s.

Let's break it down. With API RSC’s, the made-up connection introduces compressive loads on the box counterbore, sealing the primary shoulder. The pin, on the other hand, experiences tension, counterbalancing the connection and creating stress in that specific area. As tension is applied to the made-up connection, compressive loads in the box counterbore reduces, tension on the pin increases, and you start seeing tension on the box thread engagement.

Now, DSC’s present a different dynamic. During assembly, compression is evident in two areas: the box counterbore and the pin nose. Unlike API RSC’s, both pin and box experience tension to balance this compression, effectively creating two areas of stress. When tension is introduced, both areas in compression reduce, and those in tension experience higher stress to efficiently transfer tension along the string. It's like having two connections seamlessly integrated into one.

By streamlining the connection—reducing the OD and increasing the ID—DSC’s offer improved fishability and reduced friction in pumped drilling fluid. This optimization leads to decreased pressure losses, ultimately enhancing hydraulic performance (increasing hydraulic horsepower available).

Another advantage of DSC’s is their fatigue resistance. The balanced stress distribution between the shoulders mitigates peak stress in the connection, allowing for a stiffer assembly compared to a single shoulder connection. With less stress, the fatigue resistance is improved providing a longer life expectancy of the connection. This makes it ideal for a stiffer configuration when fatigue is more prone.

In conclusion, the advantages of Double Shoulder Connections extend far beyond simply increased torsional strength. With their streamlined design, enhanced hydraulic efficiency, and superior fatigue resistance, DSC’s stand as a testament to the evolution of drilling technology—providing a robust solution for those seeking better performance and efficiency in their drilling operations. Often allowing wells previously un-drillable, to now be drillable