Effects of Tension and Pressure on Torque

The amount of torque required to either further tighten or loosen the connection under tension and pressure was determined from the threaded model and the same method of summing thread forces x radii. Using 0.021 friction coef-ficient, the torques were: Nominal tapers at three turns, torque = 5 5 3 8 ft • lb Addition of 500 kips tension = 5628 ft*lb Addition of 11,220 psi pressure = 10,480 ft-lb Therefore, tension has negligible effect and pressure has a significant effect. The lack of effect by tension is due to loss of preload force on the stab flanks being equal to the increase of force on the load flanks, thereby producing no change on total torque. This behavior was also recognized by Clinedinst. Effect of Yielding on Torque Part II of this paper discusses elastic and plastic solutions with the threaded finite element model that used to determine maximum strain for 5.4 turns, 9350 psi and 660 kips tension. The assembly interference was for a fast pin and slow box, with interferences of 0.0079 in. at the pin end and 0.0231 in. at the box end. Stresses were compared in Fig. 12 of Part II and showed significant reductions due to yielding of the P-l 10 material with the stress/strain relationship shown in Fig. 11 of Part II. The same solutions were used to compare the effects of load and yielding on torque with results given in Table 7. Torque reduction due to yielding when assembled was 11 percent and the reduction at full load was 16 percent. The reductions are not particularly high but do show a source of variation in the torque/turn relationship that can occur for makeup. The elastic assembly solution can also be used to check above equation (3) for torque. The radius at the middle of the 3.25 in, length of threads was 3.418 in. The inside radius was 3.116 in. and the outside radius was 3.833 in., which gives the following calculated values