Disengageable Valve Backseat Using Eutectic Rings After Fire Exposure
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Solution Overview
Problem
Existing manual fire safe valves face challenges in maintaining their 'fire safe' designation due to changes in industry standards, such as the API 6FC being withdrawn and replaced by API 6FA, which does not allow replacement of the stuffing box before testing. This leads to increased costs and complexity, and issues like galling at the backseat interface, preventing the valve from opening after a fire test.
Innovation Solution
The implementation of a valve assembly with two eutectic rings positioned along the drive train, which melt at specific temperatures to allow the bonnet cap to move axially downward, disengaging the backseat of the stem from the bonnet backseat profile, thus preventing galling and enabling the valve to open after a fire test.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the valve is designed with a fixed backseat interface, then the valve structure is simple and reliable, but galling occurs at the backseat interface after fire exposure preventing the valve from opening
Solution Approach 1:
The backseat interface is designed to transition from a fixed, engaged state during normal operation to a disengaged state after fire exposure. The bonnet cap is made movable relative to the bonnet body, allowing the backseat profile to disengage from the stem backseat after thermal exposure, preventing galling while maintaining sealing during service.
Solution Approach 2:
The physical state of the bonnet cap changes from a constrained position to a displaced position after fire exposure. The eutectic ring melts at a specific temperature, causing the bonnet cap to move axially and disengage the backseat interface, thereby changing the mechanical parameters of the valve assembly in response to thermal parameters.
2Reliability
If the stuffing box is replaced to meet updated fire safety standards, then the valve can pass fire testing, but the valve loses its fire safe designation and requires costly modifications
Solution Approach 1:
The eutectic ring is pre-installed in the bonnet cap during manufacturing, positioned to melt at a predetermined temperature during fire testing. This preliminary placement enables the automatic disengagement mechanism to function during fire exposure without requiring post-manufacturing modifications or stuffing box replacements.
Solution Approach 2:
The eutectic ring serves as an intermediary element between the bonnet cap and the drive train. It mediates the force transmission from the actuator to the stem by melting and allowing bonnet cap movement, thereby enabling fire safety compliance without modifying the stuffing box or other critical sealing components.
3Ease of operation
If the bonnet cap is made movable to disengage the backseat, then galling is prevented and the valve can open after fire test, but the device complexity increases
Solution Approach 1:
The eutectic ring undergoes a phase transition from solid to liquid at a specific melting point during fire exposure. This phase change automatically triggers the bonnet cap movement and backseat disengagement without requiring additional actuators or complex control mechanisms, simplifying the overall device complexity while enabling post-fire operation.
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
This solution effectively maintains the valve's operational integrity by preventing galling at the backseat interface, allowing the valve to function correctly after a fire test, and adhering to updated industry standards without the need for costly modifications or component replacements.
Implementation Method 1
the first eutectic ring transitions to a flowable state from the solid state and after the second eutectic ring transitions to the flowable state from the solid state
Data Source
AI summary
A valve assembly includes a valve body, a bonnet coupled to the valve body, a stem within the stem bore, a bonnet cap axially aligned with the bonnet along a stem bore axis, and a valve drive train coupled to the stem. The valve assembly also includes a first eutectic ring, positioned between a bonnet cap interior surface and an upper shelf of the valve drive train, the first eutectic ring blocking axially upward movement of the valve drive train when in a solid state, and a second eutectic ring, positioned between a lower bonnet cap interior surface and a lower shelf of the valve drive train to fill a gap, wherein the bonnet cap is configured to move in an axially downward direction after the first and second eutectic ring transition to a flowable state.