Drill collar connections

The section modulus. Z, of the box should be 2 / times greater than the section modulus, z, of the pin in a drill collar connection. On the right side of the connection are the spots at which the critical area of both the pin (Ap) and box (A ) should be measured for calculating torsional strength. 

Figure 4-127. The drill collar connection. (After C. E. Wilson and W. R. Garrett.)...

The term drill collar originally derives from the short sub originally used to connect the bit to the drill pipe. Modern drill collars are each about 30 ft in length, and the total length of the string of drill collars may range from about 100 to 700 ft and more. 

Suppose you want to select the best connections for 9-J x 2-j -in. ID drill collars. 

Normal torque range — tabulated minimum value to 10% greater. Largest diameter shown for each connection is the maximum recommended tor that connection. If the connectons are used on drill collars larger then the maximum shown, irxrrease the torque values shown by 10% tor a minimum value. 

Before storing, the drill collars should be cleaned. If necessary, reface the shoulders with a shoulder refacing tool, and remove the fins on the shoulders by beveling. A good rust preventative or drill collar compound should be applied to the connections liberally, and thread protectors should be installed. 

The drill collars and particularly their connections are also exposed to cyclic stresses. Subsequently, these are susceptible to fatigue damage, but the changes that may influence failure arc more quickly discovered. 

Twist-offs, a rupture of the drillstring, mainly occur at tool joints or connections between drillpipe and drill collar. The main causes for twist-offs are... 

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