Compound Hub Flange Bolting for Lower Bending Stress
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Solution Overview
Problem
Traditional flange designs for high-pressure/high-temperature subsea environments face challenges in managing thermal gradients and bending stresses, leading to increased thickness and weight, which is undesirable in space-constrained subsea equipment.
Innovation Solution
The use of a flange connection with untapped or counterbored holes in the adjacent equipment piece, allowing for increased clamping length without thickening the flange, thereby reducing bending stresses on bolts, and the implementation of a compound hub flange with a groove between inner and outer hub faces to distribute loads and reduce stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the flange is increased to reduce bending stresses in bolts, then the bending stresses are decreased, but the stack height and weight of the connection increase
Solution Approach 1:
The flange is divided into two separate flanges that are connected together, with the bolt passing through both flanges and the equipment. This segmentation allows the bolt to have a longer clamping length distributed across multiple components rather than requiring a single thick flange, thereby reducing bending stresses without increasing the weight of individual flange components.
Solution Approach 2:
Instead of increasing thickness in the axial dimension, the solution extends the clamping length in the radial dimension by having the bolt pass through multiple flanges and equipment. This dimensional redistribution reduces bending moments on the bolt while maintaining connection strength without adding weight.
2Strength
If the thickness of the flange is increased to reduce bending stresses in bolts, then the bending stresses are decreased, but the stack height of the connection increases
Solution Approach 1:
The flange is divided into two separate flanges that are connected together, with the bolt passing through both flanges and the equipment. This segmentation allows the bolt to have a longer clamping length distributed across multiple flanges and equipment, thereby reducing bending stresses without increasing the overall stack height of individual components.
Solution Approach 2:
Instead of increasing thickness in the axial dimension, the solution extends the clamping length in the radial dimension by having the bolt pass through multiple flanges and equipment. This dimensional redistribution reduces bending moments on the bolt while maintaining connection strength without adding to the stack height.
3Adaptability or versatility
If traditional single hub face API style flanges are used, then standardized geometry is maintained, but they cannot adequately handle thermal gradients in HPHT environments
Solution Approach 1:
The flange is divided into two separate flanges that are connected together, with the bolt passing through both flanges and the equipment. This segmentation allows each flange to be thinner and more adaptable to thermal gradients, while the combined structure provides the necessary strength. The divided configuration enables better thermal management compared to a single thick flange.
Solution Approach 2:
The invention changes the structural parameters from a single thick flange to multiple thinner flanges connected by a bolt. This parameter change allows the structure to better accommodate thermal gradients in HPHT environments while maintaining standardized geometry compatibility through the use of conventional flange interfaces.
Data Source
AI summary
Systems: and methods for decreasing bending stress in flange bolting for a connection between a flange and an adjacent piece of equipment is provided. The flange connection includes a single flange with multiple bolts extending: therethrough. The bolts are threaded into the adjacent piece of equipment at one end, and a nut is disposed at an opposite end. of each bolt to provide a means for tightening and/or securing the flange connection. The equipment to which the flange is attached may include subsea well equipment with relatively large outer diameters. The disclosed flange connection utilizes: an initial region of a counterbored (or unthreaded) hole in the mating equipment piece just prior to the start of the thread formed through the equipment. Additionally, a compound hub flange connection is disclosed to further reduce the bending stress on the bolts.