Tubular Threaded Joint With Variable Taper to Limit Make-Up Torque
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Solution Overview
Problem
Tubular threaded joints in the oil and gas industry face challenges with high torque requirements, particularly in large diameter tubes with thin walls, where existing solutions do not adequately manage torque distribution and interference between threads, leading to potential deformation or collapse under high torques.
Innovation Solution
A tubular threaded joint design featuring tapered male and female threads with varying taper rates in specific portions to reduce interference and torque requirements, incorporating negatively inclined flanks and sealing zones to minimize stress and deformation, with optional configurations including dovetail threads and incomplete thread portions to manage crest-to-root interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional tapered threads are used in large diameter tubular members with thin walls, then the joint can be made up, but the torque required increases excessively causing potential deformation or collapse of the tubular members
Solution Approach 1:
The thread design incorporates different taper rates in different axial regions. The first portion has a first taper rate while the second portion has a second taper rate that is smaller than the first. This local variation in thread geometry allows the joint to achieve adequate interference and strength in the critical first portion while reducing torque requirements in the second portion, preventing deformation of thin-walled large diameter tubular members.
2Reliability
If thread interference is increased to achieve adequate joint strength, then the joint can withstand higher loads, but the torque required for make up increases leading to potential collapse of thin-walled tubular members
Solution Approach 1:
The threaded joint applies different taper rates to different portions of the threads. The first portion uses a larger taper rate to establish reliable interference and joint strength, while the second portion uses a smaller taper rate to reduce the torque required during make up, thereby preventing deformation and collapse of the thin-walled tubular members while maintaining joint reliability.
3Device complexity
If uniform taper rate is used throughout the thread, then the design is simpler, but the torque distribution is uneven causing high stress concentrations in specific regions
Solution Approach 1:
The thread design employs varying taper rates across different axial portions rather than a uniform taper rate. The first portion has a first taper rate and the second portion has a second taper rate that is smaller. This local differentiation optimizes torque distribution and reduces stress concentrations in critical regions, justifying the increased design complexity through improved stress management.
Data Source
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AI summary
The invention relates to a tubular threaded joint for use in the oil and gas industry. A tubular threaded joint comprising a first tubular member (1) having a pin (100) and a second tubular member (2) having a box (200), wherein the pin is an end portion of the first tubular member and comprises on its radially outward-facing surface a male threaded zone comprising a tapered male thread (150). The box is an end portion of the second tubular member and comprises on its radially inward-facing surface a female threaded zone comprising a tapered female thread (250). The male thread and female thread are configured to engage with each other when the joint is in a made-up state. The male thread and female thread are each trapezoidal and comprise a crest, a root, a load flank, and a stabbing flank. On both of the male thread and the female thread at least one of the load flank and the stabbing flank is negatively inclined. A first portion of the male thread extending from an end thereof has a first taper relative to a longitudinal axis of the first member. A first portion of the female thread extending from an end thereof has a second taper relative to a longitudinal axis of the second member, the first portion of the male thread and the first portion of the female thread are configured to engage with each other when the joint is in the made-up state. The second taper is different from the first taper such that the threads converge toward an end of the threads in the made-up state.