Retrofit of Submerged Arc Strip Electrode Automatic Surfacing Equipment

Literature Overview

This paper, authored by Jiang Yunchen from Harbin Boiler Works Co., Ltd. and published in the journal Welding (2006, Issue 2, pp. 76-77), describes a practical engineering retrofit of a submerged arc strip electrode automatic surfacing apparatus. The work addresses the need for continuous rotational surfacing on cylindrical components such as boiler drums and pressure vessel shells, where high deposition rates and uniform coverage are essential. The retrofit integrates an automatic control box with a boring machine to achieve continuous rotation during the surfacing operation, thereby eliminating the discontinuities and overlapping inconsistencies that plague manual or semi-automatic approaches.

Core Technical Content

The original equipment was designed for linear submerged arc surfacing with strip electrodes, a process that delivers deposition rates typically 3 to 5 times higher than conventional single-wire SAW. However, when applied to cylindrical geometries, the original setup required frequent stopping and repositioning, leading to uneven layer thickness and potential cracking at the restart points. The retrofit introduces a mechanical coupling between the surfacing torch carriage and a boring machine spindle, enabling the workpiece to rotate continuously under the stationary torch. An electronic control box monitors and regulates the following parameters:

The control box also incorporates interlocks that prevent the arc from striking until the flux bed is confirmed to be in place, and that halt the process immediately if the arc voltage deviates beyond a preset tolerance band.

Process Analysis and Engineering Insights

The retrofit follows a PDCA cycle in its implementation. In the Plan phase, the engineering team identified the root causes of surfacing defects on cylindrical surfaces: non-uniform layer thickness, cold cracks at restart joints, and excessive dilution from overlapping passes. The Do phase involved fabricating the mechanical adapter, programming the control box, and conducting trial runs on 12Cr1MoV boiler drum segments. The Check phase included ultrasonic thickness measurement at multiple circumferential positions and macrographical examination of cross-sections. The Act phase led to refinements in the flux distribution mechanism and the addition of a preheat controller.

From a metallurgical standpoint, the continuous rotation eliminates the thermal cycling discontinuity that occurs at each pass boundary in the original setup. This is critical for low-alloy steels such as 12Cr1MoV, where hydrogen-induced cracking susceptibility is elevated. The uniform heat input also reduces residual stress concentration at the leading and trailing edges of each pass, which is a well-documented cause of post-weld distortion in thick-walled cylindrical components.

Common Defects and Countermeasures

Study Insights and Implications

This paper is a valuable example of incremental engineering improvement rather than a revolutionary process change. The retrofit demonstrates that significant quality gains can be achieved through mechanical and control-system modifications to existing equipment, without the capital expenditure of purchasing a new machine. For engineers working in boiler and pressure vessel manufacturing, the key takeaway is that the quality of automatic surfacing on curved surfaces depends as much on the mechanical consistency of the equipment as on the welding parameters themselves. The integration of a boring machine with the surfacing system is a practical and cost-effective solution that should be considered in any facility performing large-scale cylindrical surfacing operations.