How is the blind plate force actually calculated and transmitted to the bracket?
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How is the force of the blind plate actually calculated and transmitted to the bracket? ? 》 The blind plate force is the axial force acting in the direction of fluid flow, generated by uneven internal pressures in wave compensators or valve devices installed on pipelines. I feel that the principles behind the force generated by bellows compensators and the blind plate force on valves are different. In the case of bellows, it is the pressure that causes expansion in the radial direction, which leads to contraction of the bellows along the axial direction; this creates a pulling force toward the center of the bellows. Therefore, when supporting high-temperature pipes, it is necessary to take into account that the elastic force of the bellows and the blind plate force act in opposite directions. The blind plate force generated by valves is similar to water hammer, as it results from the resistance to fluid flow through the valve – that is, kinetic energy is converted into pressure potential energy – and the direction of this force is along the direction of fluid flow. 2. Since the compensator generates a centripetal pulling force, the blind plate forces on the fixed supports between two adjacent bellows compensators cancel each other out; only at the starting and ending points of the pipeline, where such cancellation is not possible, does a blind plate force in one direction exist. Furthermore, if two adjacent compensators are not on a straight line, they cannot cancel each other out either. 3. The blind plate force generated by the valve is in one direction only; therefore, it accumulates downward in that direction until it reaches its maximum value at the final end point. So how does everyone deal with this problem?
The following opinions are all personal understandings and for reference only. I believe that the blind plate force is an external force; it represents an additional load on the pipe components resulting from changes in flow direction or momentum. This force accumulates over time as operations are carried out repeatedly. As long as there is a need to open and close the valve, this water hammer force will continue to exert an effect on the valve (mainly in terms of displacement). However, it is also counteracted by the friction and constraints inherent in the piping system, so it does not increase indefinitely. The critical point occurs when the external force acting on the pipe exceeds its own yield limit; within this range, the deformation remains elastic. The forces acting on expansion joints are considered to be internal forces of the pipeline; theoretically, they result from the product of temperature changes in the pipeline and the thermal expansion coefficient. However, due to the elasticity of the pipeline, the direction and magnitude of the thermal stresses are also influenced by the pipeline’s own layout as well as the installation positions of its associated components. This is why concepts such as compensatory action by expanders and natural compensation exist. The compensator, under the influence of the blind plate force, is generally subject to the water hammer force generated by the pipeline itself during operation, which in turn exerts a reaction force on the flexible end of the pipeline as a result of thermal stress.
This post was last edited by lp3484 on 2022-3-11 at 15:31. I am currently working on this issue and came across it by chance. Regarding question 1, I think it is necessary to distinguish between different types of expansion joints; various types of expansion joints as specified in GB12777 need to be analyzed in detail. For example, in the case of a simple internal-pressure axial expansion joint, the expansion joint elongates when under pressure, and the internal pressure force acts outward from the expansion joint. If the expansion joint is designed to compensate for expansion in the direction toward itself, then the elastic force also acts outward from the expansion joint. In that case, the force borne by the fixing frame is the sum of these two forces； For externally pressurized axial expansion joints, the joint elongates when pressure is applied; the external pressure exerts a force directed toward the inside of the joint. In this case, it represents a tensile force on the pipeline rather than a pushing force. If it is still used to compensate for thermal expansion rather than contraction, the elastic force remains directed outward from the joint, i.e., as a pushing force. I believe that the pushing force exerted by such expansion joints on the fixing brackets is the difference between these two forces ； For expansion joints with internal and external pressure balance, the internal pressure thrust is not taken into account ； Hope experts can give some advice