Premium Connection Casing and Tubing

How a Premium Connection Seals

An API round or buttress connection seals only through the interference of the thread and the thread compound filling the helical gap. Under combined tension, bending and pressure cycling, that seal can break down. A premium connection replaces this with two purpose-designed features: a metal-to-metal seal, where a machined conical or spherical surface on the pin is forced into radial interference with a matching surface in the box, and a torque shoulder, where a flat or angled shoulder on the pin butts against the box and controls exactly how far the connection can be made up. The shoulder absorbs make-up torque and prevents over-torquing the seal, while the metal-to-metal contact provides a gas-tight barrier independent of the thread compound. The result is a connection that remains gas-tight under combined load, which is essential for gas wells and for HPHT service.

ISO 13679 Qualification Levels

ISO 13679 is the standard test protocol for premium connection qualification. It defines four connection application levels, from CAL I for the least demanding service to CAL IV for the most severe. Each level specifies a series of tests combining internal pressure, external pressure, tension, compression and bending, applied at room temperature and at elevated temperature, with the connection made up and broken out repeatedly. CAL IV includes the most severe load combinations and thermal cycling. When a project specification calls for a connection qualified to a given CAL level, the supplier must provide the qualification test report from the connection manufacturer, not just a claim of suitability, so confirm this early in the procurement process.