Offset Tube Support Plate Preload for Steam Generator Vibration
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Solution Overview
Problem
Vibration due to fluidelastic excitation in heat exchanger tubes of steam generators can lead to wear and breach of the pressure barrier, especially in axial flow preheaters, where differences in secondary fluid densities cause cross flow and tube wear at support plate locations.
Innovation Solution
A tube support arrangement that includes axially spaced tube support plates with a displacement means to laterally offset the plates when the steam generator is in a hot condition, applying a preload to the heat exchanger tubes to prevent liftoff and restrain vibration, using mechanisms like sealed flexible cavities or screw thread activated jacks to impart a controlled lateral load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If tube support plates are positioned with holes substantially axially aligned when the steam generator is in a cold condition, then ease of assembly and manufacturing precision are improved, but tube vibration and wear occur under hot operating conditions due to fluidelastic excitation
Solution Approach 1:
The support plate is designed to be movable relative to the tube sheet, allowing it to change position from an aligned configuration during assembly to an offset configuration during hot operation. This dynamic adjustment enables the plate to apply a preload force on the tube that prevents vibration under thermal expansion conditions, while maintaining ease of assembly in the cold state.
2Reliability
If the support plate is offset laterally under hot conditions to apply preload on the tube, then tube vibration is restrained, but the complexity of the support structure increases
Solution Approach 1:
The support plate utilizes thermal expansion of the steam generator shell and tube sheet as the driving force for its lateral offset. As the structure heats up, differential expansion causes the support plate to move laterally relative to the tube sheet, automatically applying the required preload on the tube without requiring external actuation mechanisms or complex control systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively controls tube bundle vibration, preventing wear and maintaining the pressure barrier integrity by applying a controlled preload to the heat exchanger tubes, ensuring the tubes remain securely positioned even under varying conditions.
Implementation Method 1
A displacement means is provided for laterally offsetting at least one of the tube support plates from one other of the tube support plates when the steam generator is in a hot condition
Data Source
AI summary
A means of offsetting semi-circular tube support plates typically present in heat exchangers with cross flow baffles, such as axial flow economizers, utilizing the motive force of steam generator pressurization. The offset slightly flexes the tubes, thereby providing a preload which minimizes the potential for tube vibration and wear.