CLADDING TECHNOLOGY SHANXI CO., LTDSpectral Diagnosis of TIG Arc Temperature in Oil Pipeline Welding
Literature Overview
Published in 2006 by Zhao Huaxia and Jiao Xiangdong from Beijing University of Chemical Technology and Beijing Institute of Petrochemical Technology, this study was conducted under the National "Tenth Five-Year" 863 Program project on underwater dry pipeline repair systems (Grant No. 2002AA602012). The research applied optical emission spectroscopy to diagnose the arc temperature during TIG welding of oil pipeline components, providing real-time feedback on welding conditions that directly influence weld quality and metallurgical integrity.
Core Technical Viewpoints
The central thesis of this work is that the spectral emission characteristics of the TIG arc contain encoded information about the arc temperature, which in turn governs the heat input, dilution ratio, and microstructural evolution in the weld zone. By monitoring specific spectral lines of argon and metal vapor species in real time, the system can infer the instantaneous arc temperature and trigger corrective actions when deviations from the target window are detected.
| Spectral Feature | Wavelength Range | Diagnostic Purpose |
|---|---|---|
| Argon resonance line | 696.5 nm | Arc temperature indicator |
| Argon metastable transition | 1066.7 nm | Electron density estimation |
| Iron continuum radiation | 400–700 nm | Base metal vaporization rate |
| Titanium spectral lines | 334.8, 376.4 nm | Electrode consumption monitoring |
| Carbon Swan bands | 500–600 nm | Carbon contamination detection |
Technical Interpretation
The study established a correlation between the intensity ratio of specific argon spectral lines and the arc temperature. The argon 696.5 nm line (resonance transition) and the 1066.7 nm line (metastable transition) exhibit different temperature dependencies, and their intensity ratio follows a Boltzmann-type relationship. This allows for non-contact, non-intrusive temperature measurement with a response time of less than 1 millisecond — far superior to thermocouple-based methods that suffer from thermal lag and spatial averaging.
For oil pipeline applications, the arc temperature directly determines the dilution between the base metal and the filler metal. In the context of pipeline repair welding, where the goal is to maintain the mechanical properties and corrosion resistance of the original pipeline material, controlling the dilution ratio within a narrow window (typically 15–25% for carbon steel pipelines) is critical. The spectral diagnosis system described in this paper enables closed-loop control of welding parameters to maintain the target dilution range throughout the weld, even under variable conditions such as changes in wind speed, ambient temperature, or pipe curvature.
Engineering Practice Integration
In the context of underwater dry pipeline repair, the welding environment is constrained within a dry chamber where gas flow and arc stability are critical. The spectral diagnosis system serves as a complementary monitoring tool to conventional welding parameter controllers, providing an additional layer of quality assurance. The authors demonstrated that when the arc temperature deviated by more than 15% from the target value, the system could automatically adjust the welding current or travel speed to restore normal conditions within 2–3 seconds.
The practical implications extend to above-water pipeline welding as well, particularly for long-distance oil and gas pipelines where weld quality consistency over thousands of joints is essential. The spectral diagnosis approach can be integrated into modern automated welding systems as a real-time quality feedback mechanism, reducing the need for extensive post-weld non-destructive testing and improving first-pass acceptance rates.
Study Insights
This research represents an early application of process monitoring and control technology in welding, predating the widespread adoption of similar techniques in modern manufacturing. The methodology is directly applicable to cladding and overlay welding processes where maintaining a specific heat input is critical for controlling the dilution between the base metal and the overlay alloy. For example, in the weld overlay of Inconel 625 onto carbon steel for hydrogenation reactor cladding, controlling the dilution to below 15% is essential to preserve the corrosion resistance of the overlay layer. The spectral diagnosis approach described here provides a viable pathway for achieving such tight control in production environments.