Can the Four-Hour Installation Dwell Time Be Reduced?

A correct bolted flanged joint tightening procedure includes retorquing to restore short-term creep relaxation and embedment losses; the ASME PCC-1-2019 Tightening Method recommends a minimum of 4 hours of dwell time before retightening the bolts. It is known that in an industrial plant, maintenance costs come mostly from process downtime in addition to the labor and the tools necessary to perform the operation. Reducing the retorque waiting time would make installation quicker and avoid additional — and unnecessary — costs, returning the plant to revenue operation sooner. This paper explores whether different gasket styles should have the same dwell time between the installation and retorque, and what would be the dwell time to minimize plant downtime without compromising the gasket performance. The study was performed using a test rig based on a 4” class 300 ASME B16.5 flange equipped with eight strain-gauged bolts that correlates bolt elongation with applied stress. Four dwell times (15min, 1h, 4h and 24h) and different gasket styles and materials such as PTFE, CFG and metallic gaskets were tested. Additionally, two ASME PCC – 1 installation methods were compared and reported: Legacy Cross-Pattern Numbering System and Alternative Assembly Pattern #3. The former is the typical method for flanged joint tightening operations, while the latter offers a simpler, faster execution.

Rotator cuff tear with joint stiffness: a review of current treatment and rehabilitation

Repair of the rotator cuff tear is a joint-tightening procedure that can worsen joint stiffness. This paradoxical phenomenon complicates treatment of rotator cuff tear with joint stiffness. As a result, there is controversy about how and when to treat joint stiffness. As many treatments have been published, this review discusses the latest findings on treatment of rotator cuff tear with joint stiffness.

Experimental Study to Verify Elliptical Confidence Limit Method for Bolted Joint Tightening

The calibrated wrench method is often used for tightening. When tightening bolted joints, it is important to apply high axial tension. However, since the axial tension is indirectly applied in this method, it varies and has a distribution in the case of tightening carried out in the production line of a factory, for example. However, the calibrated wrench method is still widely used because of the simple tool and easy standardization. In our previous papers, we analyzed and discussed the main points of this research by a theoretical approach as discussed below. Conventionally, this type of distribution has been considered to lie within a rhombus (more precisely, within a rectangular area). However, when considering the tightening torque and axial tension as independent random variables, the distribution becomes elliptical. The same idea applies to the relation between the tightening torque and the equivalent stress for a bolt axis based on shear strain energy theory. On the other hand, regarding the variation in the tightening torque (tightening work coefficient a) actually applied to a bolt, it was reported by Bickford, Kawasaki, and others that it can vary by 15% or more from the target (indicated) tightening torque. However, the torques for wrenches used at actual assembly sites or under lubricated conditions were not reported. Therefore, it is necessary to experimentally verify that the relation between the tightening torque and the axial tension (axial stress) and equivalent stress of a bolt axis is distributed in an ellipse. Furthermore, the screw-thread characteristics (torque coefficient, equivalent stress coefficient, coefficient of friction, etc.) during the tightening process should be clarified by an experimental approach and observation. Thus, in this study, in experiments under dry (as-obtained) and lubricated (Loctite 263) conditions, the tool (preset-type and dial-type torque wrenches) and bolt strength classification (8.8 and 10.9) were changed, and the screw-thread characteristics were observed during actual bolt tightening and the characteristics under different conditions were analyzed. It was clearly shown that the tightening torque and the axial tension (axial stress) of a bolt axis and the equivalent stress vary with an elliptical distribution rather than a rhombic distribution. Finally, the validity of the tightening theory based on the elliptical confidence limit method was also verified experimentally.

Analysis of error influence in tooth direction upon combined cog-wheels accuracy

The solution of a problem in multi-range of cylindrical cog-wheels is in the use of banded wheels. One of the significant problems of banded wheels consists in decrease of their accuracy at assemblage. In the paper there is considered the influence of torque oscillation at threaded joint tightening upon a bend of a ring gear, and finally upon its accuracy. In the paper it is shown that the application of mechanized (pneumatic) nut-runners results in: an increase of kinematic accuracy values and smoothness of operation of an assembled cog-wheel and lose of a ring gear not less than for one degree. In the paper the attention is drawn of manufacturers to the necessity of the application of more accurate automated nut-runners and to the certification of a ring gear not only after processing, but also after assembling.

Advantage of Elliptical Confidence Limit Method for Bolted Joint Tightening Reliability

The calibrated wrench method is often used for tightening. When tightening bolted joints, it is important to apply high initial axial tension. However, since the axial tension is indirectly applied in this method, it varies and is widely distributed in the case of tightening carried out in the production line of a factory, for example. However, the calibrated wrench method is still widely used because of the simple tool used and easy standardization. Conventionally, this type of distribution has been considered to lie within a rhombus. In our previous paper, we analyzed and discussed the case when the distribution of the tightening torque and the equivalent stress of the bolted joint are considered to be independent random variables; in this case, the distribution becomes elliptical. Using this feature, a higher target tightening torque can be set than before. Finally, we established a procedure for the analysis and calculation of the optimum tightening torque for bolted joints. To ensure sufficient long-term tightening reliability to prevent breakage and loosening, a high initial axial tension and high equivalent stress can be realized using this proposed method. In this study, we analyze and discuss the case of differences in the tightening work condition (process control capability) and the tightening design condition. The tightening work coefficient a depends on the management state, the tightening working posture, and the process control capability of a tool or shop floor at a production site. According to the results of our trial calculation in Appendix A, the improvement ratio of the proposed target tightening torque is approximately 8.3% compared with the conventional method for dry friction and approximately 7.5% in the case of oily friction. Furthermore, in bolted joint tightening design, the tightening conditions under which the design conditions are satisfied are derived analytically. For the tightening design conditions of (1) a minimum axial stress of at least 50% at the yield point, and (2) an equivalent stress of 70% to 90% at the yield point, both the conventional and proposed areas of the confidence limit are obtained by precise analysis. Although the permitted limit of the tightening design condition cannot be realized by the conventional method, it can be realized by the proposed elliptical confidence limit method. Finally, we establish a method for maintaining the tightening reliability that involves applying high axial tension by increasing the target design tightening torque using the elliptical confidence limit.

Formulation of Elastic Interaction Between Bolts During the Tightening of Flat-Face Gasketed Joints

A novel mathematical model is proposed for studying elastic interaction in gasketed bolted joints. The model predicts the tension changes in tightened bolts due to the subsequent tightening of other bolts in the joint. It also predicts the final clamp load distribution after the completion of joint tightening. The model is used to investigate the effect of various factors on the elastic interaction phenomenon; factors include the gasket thickness, bolt spacing, fastener preload level, and tightening sequence of various bolts. Experimental verification is provided for the validation of the mathematical model. Experimental and analytical results are presented and discussed. The proposed model provides a good prediction of the final clamp load in the joint. Moreover, the proposed model may be used to determine the level of initial bolt tension in each bolt that would be necessary to achieve the desired level of uniform clamp load in the joint at the initial assembly.