Globe valves are commonly used to regulate flow in a pipeline. They are called globe valves due to their spherical shape with two halves of the body separated by a baffle. The flow is regulated by a screw action of a spindle using hand wheel (in manual globe valves) connected to a disc shape plug. In this project, a thermal shock analysis of a globe valve was performed in order to test its behavior. The analysis was performed based on the findings by Mathieu, J. P.. Based on these findings, the application of the pressure and temperature was on the extreme side in order to see the effect of high hot and cold thermal shock on the globe valve.
The geometry was provided by Mariusz Stanosz from GrabCAD. The geometry of the valve is shown in the figure below.
Due to symmetry, only half of the geometry was considered for the analysis. This saved both the computation time and the result size. Furthermore, the geometry was also simplified in order to easily achieve a good mesh easily. The modified geometry used for the analysis is shown in the figure below.
The geometry was meshed using parametrized tetrahedralization with moderate fineness. The mesh is shown in the figure below.
Transient static nonlinear Uncoupled thermomechanical analysis - advanced was selected as the analysis type. All the top and side bolts including the stopper and glant were bonded to the outer surfaces whereas the stem bolt and the spindle were given a sliding contact against the desired surfaces. On the other hand, Augmented Lagrange physical contact was defined between body, bonnet, and pipe joints. Symmetry was applied to the symmetric side. The pipes were constrained via remote displacement boundary condition. Outer surfaces were given a convection coefficient of 25 W/m2K at 307.15 K (35 oC).
Initially, the tightening of bolts was performed by setting their Reference temperature to 373.15 K (100 oC) in material parameters. By doing this, the pre-stressing was introduced due to sudden shrinkage of the bolts. After the tightening of the bolts, pressure of 6 MPa was applied to the internal surfaces and then kept constant. Next the hot thermal shock of 573.15 K (300 oC) was applied in 10 sec. on the internal surfaces and then kept constant until the thermal equilibrium was reached. After thermal equilibrium, again a cold shock of 307.15 K (35 oC) was applied in another 10 sec. and then kept constant until the thermal equilibrium was reached.
The analysis was run for total simulation interval of 468 sec. (7.8 min.) on 32 core machine and took around 323 min. to complete.
First figure below shows the stresses produced due to initial tightening of the bolts.
Moreover, the figures below show the temperature and stress distribution at different intervals of interest.
Interesting were the reaction forces produced on the bolt faces. Therefore, the reaction force values were requested on one of the inner faces of the top and side bolts under Result Control. The bolts were numbered in the fashion given below (upper shows top bolts whereas lower shows side bolts).
The graph below shows the reaction forces over time on side bolts.
The graph below shows the reaction forces over time on top bolts.
The graphs above are trimmed to thermal shock phases only. Therefore one can’t see the initial phase of bolts tightening and pressure application which were of no importance. The interesting thing is the fluctuation of forces in cold shock region in second graph. This could be due to several reasons. One reason could be that from the initial tightening of top bolts to the completion of the analysis, the top physical contact remained opened due to probably a poor design. The figure below shows the contact distance in y direction of the top physical contact at different intervals.
Finally, figures below show the animations of full model and the upper contact region respectively.
At the end of analysis, it can be concluded that the performance of this globe valve can be further improved under these extreme conditions by following some improvements as mentioned below:
The geometry can be improved in order to restrain the opening of the bonnet. For example, the diameter of the bonnet and body holes can be decreased in order to have more area under bolts so the tightening can close the bonnet and body properly.
The thermal properties of the material can be changed so that it has less thermal expansion factor. This will reduce the expansion of valve under extreme conditions.
A seal can be introduced between bonnet and body so that after tightening, the bolts seal will compress and thus may restrain the opening of the valve after the pressure and thermal shock are applied.
Mathieu, J. P., Rit, J. F., et al. “Thermal Shock Effects Modeling On A Globe Valve Body-Bonnet Bolted Flange Joint” arXiv preprint arXiv:1202.5125 (2012).