Zhuojin Pipe Fitting Co., LtdComparison and Selection of Duplex Stainless Steel Strip Electrode Electroslag Surfacing Processes with and without Transition Layer
Literature Overview
This study, published in 2014 in Pipelines Technology and Equipment (管道技术与设备), authored by Kong Lingwei from Shenyang Special Equipment Inspection and Research Institute and colleagues from Shenyang Oriental Titanium Industry Co., Ltd., addresses a practical engineering question: whether a transition layer is strictly necessary when performing strip electrode electroslag surfacing (SEES) of duplex stainless steel onto carbon or low-alloy steel substrates. The work is grounded in formal welding procedure qualification (WPQ) testing, making it directly relevant to engineers who must justify surfacing specifications for pressure vessels, heat exchangers, and piping systems in the petrochemical and power industries.
Core Technical Content
The authors conducted parallel qualification campaigns under two configurations:
- Process A (with transition layer): A low-carbon martensitic stainless steel or 304-type austenitic stainless steel transition layer was first deposited, followed by the duplex stainless steel overlay using strip electrode electroslag surfacing.
- Process B (without transition layer): Duplex stainless steel strip electrode surfacing was applied directly onto the base steel substrate without any intermediate layer.
Both processes were qualified through a comprehensive suite of tests including side-bend (transverse bend) fracture tests, chemical composition analysis of the weld metal, non-destructive examination (NDE), and hardness profiling across the weld cross-section.
Qualification Test Results
| Test Category | Process A (With Transition) | Process B (Without Transition) | Conclusion |
|---|---|---|---|
| Side-bend test | Pass | Pass | Equivalent ductility performance |
| Chemical composition | Within spec | Within spec | Ferrite/austenite balance acceptable |
| NDE (RT/UT) | No defects | No defects | Comparable soundness |
| Hardness profile | Within limits | Within limits | No excessive softening or hardening |
The most significant finding is that the difference in all measured indicators between the two processes was minimal, with both satisfying the applicable acceptance criteria. The authors conclude that the transition-free process represents a simpler, more cost-effective alternative that has been validated through engineering application with stable and reliable performance.
Technical Interpretation and Engineering Insights
The elimination of the transition layer is a meaningful simplification because it reduces the number of weld passes, lowers material cost, shortens production cycle time, and reduces the risk of interfacial defects between the transition and overlay layers. In duplex stainless steel electroslag surfacing, the key metallurgical concern without a transition layer is the dilution of ferrite and austenite content from the base metal into the weld pool, which could shift the microstructure away from the target 40–60% ferrite/austenite ratio. However, the electroslag process inherently produces a relatively stable weld pool with slower cooling rates compared to arc welding, which allows sufficient time for equilibrium phase formation and reduces the risk of sigma phase precipitation in the heat-affected zone.
From a standards perspective, this work supports the practice described in NB/T and GB/T welding qualification procedures, where the need for a transition layer must be justified by qualification testing rather than assumed a priori. For piping and fitting applications governed by ASME B31.3 or ASME B31.4, where duplex stainless steel overlays are specified for corrosion resistance in aggressive service environments, this qualification data provides valuable evidence for simplified welding procedures.
Key Questions and Reflections
Several practical questions arise from this study. First, the base metal composition is not explicitly detailed, which matters because dilution effects are strongly dependent on the carbon and alloy content of the substrate. Second, the long-term corrosion resistance performance, particularly susceptibility to intergranular corrosion and pitting in chloride-containing environments, should be verified beyond the mechanical and NDE criteria used in qualification. Third, the heat input range and cooling rate control during electroslag surfacing without a transition layer deserve further investigation, as these parameters directly influence the ferrite grain size and the risk of 475°C embrittlement in duplex stainless steels.
Engineering Practice Implications
For piping engineers and welding engineers involved in specifying duplex stainless steel overlays, this study reinforces the principle that process simplification should be pursued whenever qualification data supports it. The transition-free approach reduces the complexity of welding procedure specifications (WPS) and eliminates a potential quality control checkpoint at the transition/overlay interface. However, engineers should ensure that the qualification records are maintained in accordance with applicable codes, and that periodic requalification is performed to confirm long-term consistency. In my experience, the most critical control parameter in electroslag surfacing remains the electrode travel speed and slag composition, which govern both the dilution ratio and the final microstructure of the overlay.