During cementing and hydraulic fracturing of formations, Swivel Joint is one of the main components connecting the cementing truck and the wellhead. With this Swivel Joint, pipelines can be connected to each other at any angle, and the Swivel Joint can absorb most of the vibration caused by uneven pump rate.
The damping function of Swivel Joint places special requirements on components such as bearings and sealing rings. The elasticity and strength of the Swivel Joint pup and elbow must be considered together. To increase Swivel Joint service life and reliability, bearing sealing must be improved.
Figure 1 shows a Swivel Joint with a new structure. To make the sealing ring fit more tightly against the sealing surface, the position of the packing bevel opening is moved 90 degrees compared with an ordinary Swivel Joint. This makes the bevel opening face the liquid-flow direction. When elongated by 1 meter, the bevel opening becomes softer, so the packing can seal at relatively low pressure, 20 to 50 kg/cm2.
Figure 1. Pup Joint Swivel Joint
1. Threaded elbow; 2. elbow; 3. packing; 4. 10 mm diameter ball; 5. sealing ring; 6. bushing; 7. tapered seat; 8. pup; 9. packing cone; 10. sealing ring; 11. outer sleeve nut; 12. plug cover; 13. grease nipple; 14. bolt; 15. spring washer.
These measures reduce the possibility that abrasive debris will fall into the clearance between packing and contact surface.
During use of Swivel Joint, it was observed that the outside diameter of the sealing ring wears fastest at part P, shown in Figure 1. Under high pressure, the packing starts to move toward clearance B and is quickly washed out at part P.
To prevent washout, the packing is assembled with metal ring 1, as shown in Figure 2. The ring is stamped from 0.5 mm thick steel plate and placed in the mold, then rubber is poured over it for forming.
Figure 2. Metal ring of Swivel Joint packing
1. Ring; 2. rubber
To reduce dirt entering the bearing from the end face, direction V, a rubber sealing ring is installed in front of the bearing. It can protect the bearing from dirt until the bearing wears. When a clearance is formed between ball and bearing groove, shown in Figure 3, if vibration is large, dirt enters the clearance between connection parts and penetrates into the bearing in direction K, as shown in Figure 3. Therefore, dirt cannot be completely prevented from entering the bearing. To remove dirt from the bearing after operation and keep the bearing properly lubricated, holes are made in plug cover 12 and grease nipple 13 is installed. Fresh lubricant is injected into the bearing through this grease nipple with a pressure gun to discharge contaminated lubricant. In this way, bearing lubrication can be restored after each operation, improving Swivel Joint service life.
Figure 3. Swivel Joint sealing packing
