Three-Start Drill Pipe Threading to Prevent Seizure
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Solution Overview
Problem
The existing roto-percussion pipes with standard two-start threads often seize during connection or disconnection, rendering the drill string unusable, which is a significant drawback in achieving the desired drilling length.
Innovation Solution
A roto-percussion pipe with a tubular portion made of N80 special steel, featuring a 3-start female and male thread with beveled entry portions and surface-hardened couplings, facilitated by mechanical centering profiles and automatic welding, minimizes the risk of seizure by ensuring coaxial alignment and secure connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard two-start threads are used for connection, then the threading process is simpler and faster, but the thread seizes during connection or disconnection making the drill string unusable
Solution Approach 1:
The patent applies different properties to different parts of the thread: the entry portion has a removed commencement spiral forming a bevel for easy engagement, while the main thread body maintains the three-start configuration for smooth operation. This local differentiation prevents seizure while maintaining threading efficiency
Solution Approach 2:
The patent changes the thread parameter from standard two-start to three-start configuration, which fundamentally alters the threading mechanics to prevent seizure. Additionally, the surface hardening treatment (nitriding) changes the surface properties of the coupling to reduce friction and prevent galling during connection and disconnection
2Reliability
If three-start threads are used to prevent seizure, then thread reliability improves, but the threading complexity increases
Solution Approach 1:
The entry portion of the thread is pre-formed with a bevel by removing the commencement spiral, which prepares the thread for easy engagement and alignment. This preliminary preparation simplifies the overall connection process despite using three-start threads, as the bevel guides the male thread into proper alignment automatically
3Reliability
If couplings are surface-hardened to prevent seizure, then connection reliability improves, but the welding process becomes more complex
Solution Approach 1:
The coupling manufacturing process is segmented into distinct stages: surface hardening (nitriding) is applied first to the entire coupling, then the entry portion is mechanically removed to expose the non-hardened base metal. This segmentation allows the coupling to have both the seizure-resistant hardened surface and the weldable soft core, resolving the contradiction between connection reliability and welding ease
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
The 3-start thread design and nitriding treatment enhance the coaxial alignment and longevity of the pipes, preventing seizure and extending their operational life, thus ensuring reliable and efficient drilling operations.
Implementation Method 1
both the couplings being made of 42 Cr Mo 4 steel, before being welded to the tubular portion they being subjected to surface hardening treatment, preferably nitriding
Implementation Method 2
a first weld seam joining together the couplings and the tubular portion of the pipe
Data Source
Figure 1~5
Figure 6~7
AI summary
A roto-percussion pipe, comprising a tubular portion having at its ends a female coupling carrying a female thread, and a male coupling carrying a male thread, said male coupling and female coupling enabling the pipe to be connected to other pipes identical therewith to form a roto-percussion drill string of the required length, said threads having at least three starts.