Two-Step Steel Pipe Thread Connection to Prevent Thread Galling
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Solution Overview
Problem
Galling occurs easily on either the inner or outer threads during the make-up of a two-step threaded connection for steel pipes due to misalignment and excessive loads on the threads, leading to unstable contact and potential damage.
Innovation Solution
A threaded connection design where the inner and outer threads contact simultaneously, with specific geometric configurations and shoulder surfaces to ensure proper alignment and distribute loads evenly, preventing galling by satisfying expressions (1) and (2) related to thread engagement and shoulder surface contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-step threaded connection is made up, then the connection can be assembled with inner and outer threads, but galling occurs easily on either the inner or outer threads due to misalignment and excessive loads
Solution Approach 1:
The patent applies preliminary action by providing a shouldered pin and shouldered box where the shoulders contact first to establish proper alignment before the threads engage. This preliminary shoulder contact prevents misalignment during thread engagement, thereby preventing galling on the threads while ensuring stable thread contact.
2Ease of operation
If the inner threads contact before the outer threads, then the connection can be made up, but the inner threads receive excessive loads causing galling
Solution Approach 1:
The shouldered pin and shouldered box are designed so that the shoulders contact first during the make-up process, establishing proper alignment before thread engagement. This preliminary action ensures that both inner and outer threads contact simultaneously and receive loads evenly, preventing excessive loads on the inner threads and eliminating galling.
3Ease of operation
If the outer threads contact before the inner threads, then the connection can be made up, but the outer threads receive excessive loads causing galling
Solution Approach 1:
The shouldered pin and shouldered box provide preliminary shoulder contact that establishes proper alignment before thread engagement. This ensures simultaneous contact of both inner and outer threads during make-up, distributing loads evenly and preventing excessive loads on the outer threads that would cause galling.
4Device complexity
If threads engage without preliminary alignment, then the make-up process is simpler, but misalignment occurs causing unstable contact and galling
Solution Approach 1:
The patent incorporates shouldered pin and shouldered box components where the shoulders serve as preliminary alignment features. These shoulders contact first to establish proper axial and angular alignment before the threads engage, ensuring stable thread contact and preventing galling. The added shoulder features increase device complexity slightly but dramatically improve reliability.
Data Source
AI summary
A threaded connection for steel pipe is provided in which galling does not easily occur on any of the inner and outer threads. A threaded connection for steel pipe 1 includes a pin 10 and a box 20. The pin 10 includes: a nose 12; a tapered inner male thread 14; a tapered outer male thread 17; a pin inner sealing surface 13; a pin intermediate shoulder surface 18; and a pin intermediate sealing surface 16. The box 20 includes: a tapered inner female thread 24; a tapered outer female thread 27; a box inner sealing surface 23; a box intermediate shoulder surface 28; and a box intermediate sealing surface 26. Each of the inner male thread 14, outer male thread 17, inner female thread 24 and outer female thread 27 includes a perfect thread portion 141, 171, 241, 271. Each perfect thread portion includes an inner end located relatively close to the tip of the pin 10 and an outer end located relatively close to the end of the pin 10 opposite to its tip. The threaded connection for steel pipe 1 satisfies the following Expressions (1) and (2):x1+L1<X2 (1), andu1+L2<U2 (2).