Team Up Chucks to Thread Large Diameter OCTG

In the first article in this series, we related the story of how SMW Autoblok revolutionized the oil drilling industry with its Big Bore® chucks and self-centering technology for pipe of 14.8” or less in diameter (see SMW Autoblok Innovates Oil Country Workholding). The next challenge in our sights was how to address the problem of auto-centering larger diameter pipe afflicted with end hooks and sags.

Direct threading is one method of joining two pieces of pipe together to achieve greater length. An inner diameter (box) connection is matched with an outer diameter (pin) connection. Needless to say, it is vital these match up perfectly. The big question is: How do you clamp on a larger diameter piece of bent pipe to hold it steady while maintaining an accurate center line for machining the thread?

image002Chuck Team Up
As you can imagine, manhandling a 40-foot section of large diameter pipe so it aligns to center is a daunting task. One chuck by itself is just not up to the job. For any pipe over a 15” diameter, we recommend a combination of three chucks in three different positions on the pipe: the BB-AZ2G in the front, the BB-AS 1000 on the rear and the IN-D 500 on the tailstock.

Centering the Tube
When you load your pipe you need a centering mechanism, which in this case, comes off the tailstock of the machine. We mount the IN-D 500, which is a very rigid, solid hydraulic chuck. The chuck rides on the tailstock which moves into the centering position via the tailstocks servomotor and ball screw and is then actuated with a hydraulic cylinder mounted to the back side of the tailstock. The front chuck then compensate clamps, and the tailstock and chuck are retracted out of the way so that the pipe can be threaded.

image004_croppedCompensating For the Bend
Putting pneumatic chucks on both the front and rear of the pipe keep it on center throughout the process. The BB-AS 1000 is a compensating chuck that is mounted on the rear. Its jaws can move equally or, by shifting air through a different port in the chuck, individually. The individual movement (unequal force exerted by each jaw) is what compensates for the bend in the pipe and keeps it on centerline. The BB-AS 1000 is able to clamp off center up to one inch.

The BB-AZ2G is mounted in the front of the lathe. It also has air-adjustable jaws. When the pipe is loaded, the chucks are able to compensate and put the pipe on center fast. It is important that both compensating chucks have an extra long jaw stroke for safe loading of pipe without hitting the jaws and safe unloading of the machined pipe with no damage to the finished thread.

Acting in combination, the three chucks enable premium threading on big diameter pipe that is leakproof and will withstand the pressures of oil field use. But sometimes threading is not the best option. Our next post in this series will discuss joining sections through the use of couplers.

If you would like to discuss your service requirements in oil country or anywhere in the United States, please contact us.