Steel Pipe Joint Thread Structure for Higher Fastening Torque
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Solution Overview
Problem
The existing steel pipe joint structure for oil country tubular goods faces challenges in achieving a sufficient fastening torque without increasing the outer diameter or wall thickness of the steel pipes, which affects the sealability and pressure resistance.
Innovation Solution
The proposed steel pipe joint structure incorporates a unique thread configuration where the pin front part includes a pin front parallel thread part and a pin complete thread part, while the box rear part includes a box rear incomplete thread part. This configuration allows for a larger critical section area without increasing the pipe dimensions, enhancing the fastening torque and sealability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the critical section area of the thread part is increased to enhance strength and rigidity, then the fastening torque and sealability are improved, but the outer diameter and wall thickness of the steel pipe must be increased
Solution Approach 1:
The patent applies local quality by creating an incomplete thread part with a larger root diameter only at the critical section (end portion of the engagement region), while maintaining the standard thread configuration in other areas. This localized modification increases the critical section area and moment of inertia specifically where needed for strength and rigidity, without requiring an overall increase in pipe outer diameter or wall thickness.
Solution Approach 2:
The thread part is segmented into a complete thread part and an incomplete thread part. The incomplete thread part is specifically positioned at the end portion of the engagement region where the critical section exists. This segmentation allows the critical section area to be increased locally while keeping the rest of the structure compact, resolving the contradiction between strength enhancement and volume control.
2Strength
If the critical section area is increased by increasing wall thickness, then the fastening axial force resistance is improved, but the fastening torque is reduced due to decreased shoulder part contact area
Solution Approach 1:
The invention applies local quality by modifying only the root diameter at the critical section of the thread part, specifically at the end portion of the engagement region. This localized increase in root diameter enhances the moment of inertia and fastening axial force resistance without affecting the shoulder part contact area, thereby maintaining fastening torque while improving strength.
3Reliability
If the thread configuration is modified to increase critical section area, then the sealability and pressure resistance are improved, but the manufacturing complexity increases
Solution Approach 1:
The patent applies partial action by creating an incomplete thread part rather than modifying the entire thread configuration. The incomplete thread part is formed only at the end portion of the engagement region where the critical section exists, using a thread cutting tool that stops before completing the full thread depth. This partial modification achieves the desired increase in critical section area and improvement in sealability and pressure resistance without requiring complex manufacturing processes.
Data Source
AI summary
A steel pipe joint structure connects a first steel pipe and a second steel pipe with each other, the first steel pipe having an external thread, the second steel pipe having an internal thread, wherein the first steel pipe has the external thread, and the second steel pipe has the internal thread. The external thread part includes a pin front parallel thread part, and a pin complete thread part, and the internal thread part includes a box rear incomplete thread part, and a box complete thread part. The box rear incomplete thread part and the pin front parallel thread part are threadedly engaged with each other and, in cross section including a pipe axis, a root of the pin front parallel thread part has a larger width than a root of the pin complete thread part.