Telescopic Riser Joint Mode Switching for Fatigue Reduction
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Solution Overview
Problem
Existing high-pressure riser systems for floating offshore installations face challenges in safely performing manual work due to hazardous vertical movements and excessive forces, leading to inefficiencies and limited operational time, with prior solutions using excessive material and resulting in a stiff, costly, and fatigue-prone riser design.
Innovation Solution
A telescoping riser arrangement that switches between high and low pressure modes, where a low-pressure inner sleeve reciprocates within a high-pressure outer sleeve, with a locking mechanism and seals to maintain a water column, allowing for reduced material usage and remote operation, and a locking mechanism actuated by hydraulic pistons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a conventional telescopic joint is used for high pressure risers, then the riser can withstand high pressure, but the inner and outer sleeves must be dimensioned to withstand full riser tension and internal high pressure simultaneously, resulting in excessive material usage, increased weight, and higher costs
Solution Approach 1:
The riser is divided into two functional segments: a high-pressure outer sleeve that maintains pressure containment, and a low-pressure inner telescopic sleeve that handles only heave movements. This segmentation allows each component to be optimized for its specific function, with the inner sleeve being significantly lighter since it doesn't need to withstand full pressure and tension loads.
Solution Approach 2:
Different parts of the riser assembly have different structural requirements. The outer sleeve is designed with high strength properties to contain pressure, while the inner telescopic sleeve can use lighter materials since it only experiences low pressure during telescoping operations. This local differentiation of structural quality reduces overall weight while maintaining necessary pressure resistance.
2Strength
If the inner and outer sleeves are both dimensioned to withstand full high pressure and tension, then the riser can handle high pressure loads, but the outer sleeve needs to be of large dimension to accommodate the high pressure inner sleeve, resulting in superfluous material and increased weight
Solution Approach 1:
The functional segmentation separates pressure containment (outer sleeve) from telescoping movement (inner sleeve). The inner sleeve doesn't need to be large or heavy since it only handles low pressure during telescoping, while the outer sleeve provides the necessary pressure containment with appropriate, not excessive, dimensions.
Solution Approach 2:
The telescoping function is extracted from the high-pressure containment function. The inner telescopic sleeve is removed from the high-pressure load path during telescoping operations, allowing it to be much smaller and lighter than a conventional single-function design would require.
3Strength
If a stiff riser is used to withstand high pressure, then the riser can maintain structural integrity under pressure, but the stiff riser produces very high bending moments through rotary/work floor/moonpool, resulting in limited fatigue life
Solution Approach 1:
The riser transitions from a static, stiff structure to a dynamic system with controlled flexibility. The inner telescopic sleeve can move relative to the outer sleeve during heave, allowing the riser to accommodate movements without generating excessive bending moments. This dynamic capability extends fatigue life while maintaining necessary structural integrity through the outer sleeve's pressure containment design.
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 design enables safer manual work by stabilizing the upper riser during heaving movements, reduces material usage and weight, and extends the fatigue life of the riser by optimizing the structural integrity and operational flexibility.
Implementation Method 1
a locking mechanism actuated by hydraulic pistons
Implementation Method 2
seals to maintain a water column
Data Source
AI summary
Telescoping riser arrangement forming part of a riser string (1) connecting a subsea well and a floating installation. The riser arrangement is adapted to be switched between a high pressure mode, in which an upper part of the riser assembly will move vertically with respect to the installation when the installation heaves, and a low pressure mode in which the upper part of the riser assembly will move vertically along with the installation when the installation heaves. In the low pressure mode, a low pressure inner sleeve (9) is adapted to reciprocate inside a high pressure outer sleeve (1a), the reciprocating heave path being above the position of the inner sleeve (9) in the high pressure mode. In the high pressure mode, the telescoping section of the low pressure inner sleeve (9) is enclosed within a high pressure compartment.