Pulsed Current Root Pass Welding for Pipe Joints
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional gas metal arc welding (GMAW) processes face challenges in achieving adequate penetration and controlling heat input during open root welding, leading to issues like lack of penetration, poor sidewall fusion, and high weld hardness, which are exacerbated by the need for high travel speeds and preheating in the petrochemical and process piping industries.
Innovation Solution
A method and system that generate a substantially periodic electric welding waveform with a base cycle, peak current phase, tail-out current phase, and heat-increasing current pulses during the background phase to control heat input and improve penetration without increasing weld puddle fluidity, allowing for lower hardness and faster travel speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional GMAW processes are used to increase travel speed, then productivity improves, but penetration and sidewall fusion deteriorate
Solution Approach 1:
The patent applies periodic action by using pulsed current welding instead of continuous current. The welding current is delivered in periodic pulses with distinct phases (background current phase and heat-increasing current phase) that repeat cyclically. This periodic delivery allows the weld pool to cool between pulses while still accumulating sufficient heat for penetration, enabling faster travel speeds without sacrificing fusion quality.
Solution Approach 2:
The patent implements dynamics by making the welding parameters dynamic and time-dependent. The current level, voltage, and other parameters vary continuously during each pulse cycle rather than remaining static. This dynamic control allows optimization of both penetration (during heat-increasing phase) and travel speed (by controlling overall energy input), resolving the contradiction between speed and quality.
2Manufacturing precision
If heat input is increased to improve penetration, then manufacturing precision improves, but weld hardness and HAZ hardness increase
Solution Approach 1:
The periodic pulsed current delivers heat in controlled intervals rather than continuously. The background current phase provides base heating for penetration, while the heat-increasing phase adds supplemental heat. The periodic nature allows heat dissipation between pulses, preventing excessive heat accumulation that would cause high hardness, while still achieving adequate penetration through cumulative heat input.
Solution Approach 2:
The patent changes the temporal parameters of heat input by introducing pulse frequency, pulse width, and duty cycle as controllable variables. By adjusting these parameters, the total heat input can be optimized to achieve penetration without excessive heat accumulation. The parameter changes allow decoupling of penetration depth control from total heat input control, resolving the hardness contradiction.
3Productivity
If welding travel speed is increased to improve productivity, then time consumption decreases, but heat input control becomes more difficult
Solution Approach 1:
The periodic pulsed current system inherently provides heat input control through the duty cycle (ratio of pulse on-time to total cycle time). By adjusting the duty cycle, frequency, and pulse width, the average heat input can be precisely controlled even at high travel speeds. This periodic framework simplifies control compared to attempting continuous adjustment at high speeds, as the discrete pulses are easier to regulate and measure.
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 solution enhances penetration, reduces weld hardness, and increases welding travel speeds while minimizing preheating requirements, resulting in improved quality and efficiency for both open and closed root welding processes.
Implementation Method 1
a series of electric arc pulses are generated between an advancing welding electrode and a root pipe joint
Implementation Method 2
at least one heat-increasing current pulse during the background current phase providing a heat-increasing current level
Data Source
AI summary
A method and a system for forming a root pass weld for a root pipe joint. A substantially periodic electric welding waveform is generated and a series of electric arc pulses are generated between an advancing welding electrode and a root pipe joint in response to the electric welding waveform. The electric welding waveform includes a base cycle having a background current phase providing a background current level, a peak current phase providing a peak current level, a tail-out current phase providing a decreasing tail-out current level, and at least one heat-increasing current pulse during the background current phase providing a heat-increasing current level being above the background current level.