Cementing trucks and mobile pump units used for oilwell service are connected by detachable swivel joints. The swivel joint consists of quick make-up connection threads, rubber seal rings and union-type pipe fittings that allow each section of line to move freely during field installation. The nominal diameter is 60 mm.
New union connector structure
The newly developed union connector structure is characterized by good sealing performance, especially at low pressure of 40-60 kgf/cm2, where the clearance is very small. A separate plug is used for the steel-ball raceway, increasing the raceway opening by 5 mm and thereby reducing the inclination angle of the swivel joint.
The proposed seal-ring profile avoids damage to the mating surface under the seal ring during movement between workshops and ensures that the seal ring has a pre-compression allowance of 0.3-0.5 mm during assembly.
The developed union connector conforms to modern technical practice. Its parts have good manufacturability in mass production, so the equipment and tooling used to manufacture these parts can be further improved, with mechanization and automation introduced into the process.
Five new union connectors were tested on a Model 400 cementing truck. Over two years, the unit operated for about 1,000 hours and completed various operations including cementing, fracturing, induced flow and squeeze cementing. In nearly 100 operations, each job involved continuous operation for 1 to 5 hours at pressures from 30 to 350 kgf/cm2. After all union connectors had operated for 700 hours, the seal rings were replaced; all metal parts remained in good condition.
During the completion of oilwell process operations, no failure of the union connector seal was found. The new union connector does not require monthly maintenance. After 2-3 months of operation, the steel balls only need to be lubricated once without disassembling the connection.
The developed union connector has already been put into batch production.
