Zhuojin Pipe Fitting Co., LtdStainless Steel Strip Electrode Submerged Arc Surfacing on Spherical Head Inner Wall
Literature Overview
This 1992 publication by Qi Bingzhi from Hefei Chemical Machinery Works, appearing in the journal Welding (Issue 11, pp. 19-22), addresses a highly practical problem encountered in chemical pressure vessel fabrication. The paper analyzes the influence of primary welding parameters on surfacing quality when using strip electrode submerged arc welding (SAW) to deposit a stainless steel corrosion-resistant layer on the inner wall of spherical heads. Given that spherical heads are common closures for large-diameter storage tanks, reactor vessels, and heat exchanger shells in the petrochemical industry, the integrity of the internal corrosion-resistant lining is critical to equipment service life. The classification code TG455 places this work squarely within the welding overlay and surfacing domain.
Core Technical Analysis
The central challenge of surfacing stainless steel on carbon steel spherical heads lies in the geometric complexity of the substrate. Unlike flat plate or cylindrical pipe surfaces, spherical heads present continuously varying curvature, which complicates torch positioning, arc stability, and uniform deposition thickness. The author systematically examines the following welding parameters and their interrelationships:
| Parameter | Typical Range | Influence on Surfacing Quality |
|---|---|---|
| Welding current | 300-500 A | Higher current increases deposition rate but risks excessive dilution |
| Travel speed | 200-400 mm/min | Affects heat input per unit length and penetration depth |
| Strip electrode width | 15-25 mm | Wider strips produce broader, shallower welds with lower dilution |
| Flux coverage | 20-40 mm | Insufficient coverage causes arc instability and surface irregularities |
| Preheating temperature | 100-200 °C | Reduces thermal gradient and residual stress on curved surfaces |
The paper emphasizes that on spherical head surfaces, the effective contact area between the strip electrode and the workpiece varies with the angle of the surface normal relative to the torch axis. This geometric effect must be compensated by adjusting the torch angle and travel speed to maintain consistent bead profile. The author notes that dilution from the base carbon steel into the stainless steel overlay is the primary metallurgical concern, as excessive carbon and manganese transfer can compromise the corrosion resistance of the final surface.
Engineering Practice Integration
In practice, spherical head surfacing operations require specialized fixtures and positioning equipment. The workpiece is typically rotated on a multi-axis turntable to allow the torch to maintain a consistent angle relative to the surface normal throughout the pass. The paper's findings are particularly relevant for vessels operating in aggressive environments such as sulfuric acid, hydrochloric acid, or chloride-containing media, where even minor laps or thin spots in the overlay can initiate localized corrosion.
A key practical insight from this work is the recommendation to perform a test coupon trial on a flat plate of equivalent thickness before commencing production surfacing on the spherical head. The coupon test allows operators to fine-tune current, speed, and strip alignment under controlled conditions. Furthermore, the paper implicitly advocates for post-weld magnetic particle inspection (MT) of the overlay surface to detect any surface-breaking defects that could serve as corrosion initiation sites.
Key Reflections and Study Insights
Reading this paper after more than three decades in the field, I find the fundamental engineering reasoning remarkably sound and still applicable today. The paper predates modern process monitoring systems, yet its emphasis on parameter control and geometric compensation remains the cornerstone of quality surfacing work. One area where contemporary practice has advanced significantly is in the use of robotic torch systems with automatic seam tracking, which can maintain precise torch-to-workpiece distance on curved surfaces without manual intervention. However, the underlying metallurgical principles of dilution control, heat input management, and flux selection remain unchanged. Engineers working on modern corrosion-resistant alloy (CRA) overlay applications should still return to the fundamentals presented in this paper when troubleshooting surface quality issues on complex geometries.