CLADDING TECHNOLOGY SHANXI CO., LTDArc Termination Defect Analysis in Submerged Arc Strip Cladding
Literature Overview
This 2012 publication by Wang Bin, Zhang Junling, Yang Fei, and Zhou Cui, jointly authored by researchers from Southwest Petroleum University and Atlantic Welding Materials Co., Ltd., addresses a persistent and under-discussed quality issue in submerged arc welding (SAW) strip cladding operations. The study investigates arc termination defects — a category of weld discontinuities that occur at the end of each cladding pass — which are particularly critical in multi-pass weld overlay operations used for corrosion and wear protection of pressure vessels and structural components. The authors systematically analyzed the formation mechanisms, morphological characteristics, and engineering consequences of these defects, providing a foundation for improved process control in industrial cladding applications.
Core Technical Findings
The arc termination region in SAW strip cladding represents a thermally and metallurgically unstable zone. When the arc is extinguished at the end of a pass, the molten pool contracts rapidly, and the solidification front advances in an uncontrolled manner. This creates several characteristic defects:
| Defect Type | Morphology | Root Cause | Severity |
|---|---|---|---|
| Crater crack | Radial or transverse cracks at weld terminus | High residual stress concentration + hydrogen embrittlement | Critical |
| Undercut at termination | Concave groove at arc end | Insufficient heat input during arc decay | Moderate |
| Lack of fusion | Partial bonding failure at pass-to-pass interface | Inadequate overlap and poor wetting at termination | Critical |
| Porosity cluster | Gas inclusions near arc crater | Incomplete shielding during arc extinction | Moderate |
| Incomplete penetration | Reduced bond strength at termination zone | Rapid cooling rate exceeding solidification equilibrium | Critical |
The authors identified that the defect formation is governed by three primary factors: the cooling rate at arc termination (typically 5–20 °C/s depending on base metal thickness), the hydrogen content in the weld metal (exceeding 15 mL/100g leads to increased cracking susceptibility), and the overlap ratio between adjacent passes (below 30% overlap increases lack-of-fusion probability significantly).
Process Parameters and Defect Sensitivity
The study examined how key SAW process parameters influence arc termination quality. Strip cladding typically employs flux-cored wire strips with widths of 50–80 mm, operating currents of 400–800 A, and travel speeds of 150–400 mm/min. The following parameter windows were identified as critical for minimizing arc termination defects:
| Parameter | Acceptable Range | Defect-Prone Range | Recommended Value |
|---|---|---|---|
| Travel speed (mm/min) | 200–350 | <150 or >400 | 250–300 |
| Welding current (A) | 500–700 | <400 or >800 | 600 |
| Arc voltage (V) | 28–35 | <25 or >38 | 30–32 |
| Interpass temperature (°C) | 150–300 | <100 or >400 | 200–250 |
| Pass overlap (%) | 30–50 | <25 | 35–40 |
| Flux coverage thickness (mm) | 15–25 | <10 | 18–20 |
The cooling rate at the arc termination is particularly sensitive to the base metal thickness. For base plates thinner than 12 mm, the cooling rate can exceed 15 °C/s, promoting martensitic transformation in high-carbon overlay alloys and increasing the risk of cold cracking. For thicker base plates (>25 mm), the thermal mass provides better heat retention, reducing the cooling rate below 8 °C/s and allowing more favorable microstructural evolution.
Engineering Practice Implications
In the fabrication of clad-plate pressure vessels — particularly hydrogenation reactors and high-pressure storage vessels — the quality of each cladding pass directly affects the integrity of the corrosion-resistant overlay layer. A single arc termination defect can serve as a stress concentration site and a potential initiation point for intergranular corrosion or hydrogen-induced cracking. The study recommends the following engineering countermeasures:
- Implement arc termination procedures that include a brief dwell period (0.5–1.5 seconds) at the end of each pass to allow controlled solidification.
- Use a tapered or stepped termination technique where the wire feed rate is gradually reduced while maintaining arc stability.
- Ensure adequate flux coverage during arc termination to prevent atmospheric contamination and nitrogen pickup.
- Apply post-weld heat treatment (PWHT) at 600–650 °C for 2 hours per 25 mm of thickness to relieve residual stresses and reduce hydrogen content.
- Perform ultrasonic testing (UT) or phased array ultrasonic testing (PAUT) specifically targeting the arc termination zones of each cladding pass.
Key Questions and Reflections
The study raises an important question: can arc termination defects be fundamentally eliminated through process optimization alone, or do they represent an inherent limitation of the SAW process? From my experience in bimetal pressure vessel fabrication, I believe the latter is closer to the truth — arc termination defects can be minimized but not entirely eliminated. The key lies in managing their severity and ensuring they fall below the acceptance criteria defined in relevant standards such as NB/T 47014 and ASME IX. The study's systematic approach to defect classification and parameter correlation provides a valuable framework for developing site-specific welding procedure specifications (WPS) that address this particular quality challenge.
Study Insights and Implications
This publication, though published over a decade ago, remains highly relevant to current engineering practice. The fundamental physics of arc termination in SAW has not changed, and the defect mechanisms identified continue to apply to modern high-productivity strip cladding operations. The study's emphasis on the interplay between cooling rate, hydrogen content, and overlap ratio provides a tripartite framework that I have found useful in diagnosing cladding quality issues on the shop floor. Future work should extend this analysis to include the effects of automated wire feeding systems and real-time monitoring technologies on arc termination quality, as these technologies are increasingly deployed in modern cladding operations. The collaboration between academia (Southwest Petroleum University) and industry (Atlantic Welding Materials) exemplifies the productive model of joint research that addresses real-world manufacturing challenges.