Submerged Arc Strip Cladding of Stainless Steel on Low-Alloy Steel Surface

Literature Overview

This study focuses on the submerged arc welding (SAW) strip cladding process for applying a corrosion-resistant stainless steel layer onto low-alloy steel base plates. The research addresses critical aspects including process parameter optimization, dilution control, bond strength evaluation, and compliance with pressure vessel fabrication standards. Strip cladding—also known as strip welding or double-wire SAW cladding—is a highly productive method for producing stainless steel clad plate, widely used in the fabrication of pressure vessels, heat exchangers, and chemical processing equipment.

Core Technical Content

Process Description and Equipment Configuration

Submerged arc strip cladding employs two consumable electrodes (typically solid stainless steel wire or flux-cored wire) fed simultaneously from opposite sides of a base plate, with a continuous strip of flux providing shielding and slag coverage. The process achieves deposition rates of 15–30 kg/h, significantly higher than conventional single-wire SAW cladding (5–10 kg/h). The equipment configuration includes:

A pair of wire feed mechanisms (push-pull or pull-type)
A flux distributor and recovery system
A torch holder with adjustable travel speed
A flux trough or flux table
A preheating and post-weld heat treatment furnace

The study emphasizes that the flux composition is critical for controlling dilution and preventing defects. A low-silica, low-fluorine flux (such as AS-FB-1 or equivalent) is recommended to minimize chromium loss from the overlay layer while maintaining arc stability and slag fluidity.

Process Parameter Optimization

The study presents a systematic investigation of the effects of welding current, arc voltage, travel speed, wire feed rate, and flux coverage thickness on the dilution rate, overlay thickness, and defect formation. The optimal process parameters identified are summarized below:

Parameter	Optimal Range	Effect on Dilution
Welding current	600–800 A	Higher current increases penetration and dilution
Arc voltage	28–34 V	Higher voltage increases arc width and dilution
Travel speed	300–500 mm/min	Higher speed reduces heat input and dilution
Wire feed rate	8–12 m/min (per wire)	Must match travel speed for stable arc
Flux coverage thickness	15–25 mm	Adequate coverage prevents spatter and oxidation
Heat input	1.5–3.0 kJ/mm	Lower heat input reduces dilution

The study demonstrates that the dilution rate can be controlled to below 30% by using a travel speed of 400–500 mm/min and a heat input of 1.5–2.0 kJ/mm. However, achieving dilution below 20% requires more aggressive parameter settings that may compromise deposition efficiency and increase the risk of lack of fusion.

Dilution Control and Microstructural Analysis

The dilution zone between the base metal and the overlay layer is the critical region determining the corrosion resistance of the clad plate. The study examines the microstructure at three locations: the overlay surface, the dilution zone, and the base metal/overlay interface. The overlay surface exhibits a fully austenitic microstructure (304/316 composition), while the dilution zone shows a ferrite-austenite mixed structure with ferrite content ranging from 5% to 25% depending on the dilution rate. The interface region contains a thin band of martensite or delta ferrite, which can be detrimental to corrosion resistance if not properly controlled.

The study recommends that the dilution zone be eliminated by solution heat treatment at 1050–1100 °C with water quenching, or that the overlay thickness be increased to ensure that the dilution band falls outside the critical region. For pressure vessel applications, the overlay thickness should be at least 3 mm (preferably 5 mm) to provide adequate corrosion resistance after accounting for machining allowance and dilution.

Standards and Quality Control

The study references several key standards governing the fabrication and inspection of submerged arc strip clad plate:

GB/T 150.4-2011: Specifies requirements for clad plate pressure vessels, including minimum overlay thickness, dilution limits, and mandatory post-weld heat treatment.
NB/T 47002.3-2009: Provides technical requirements for the design and fabrication of clad plate pressure vessels.
ASME VIII Div. 1: Appendix B specifies requirements for hydrogen service pressure vessels, including overlay thickness and dilution control.
ASME IX: Qualification of welding procedures and welders, including SAW strip cladding procedures.
ASTM A263/A264/A265: Specifications for austenitic stainless steel clad plate, including chemical composition, mechanical properties, and corrosion resistance requirements.

The quality control plan for submerged arc strip cladding should include the following inspection steps:

Visual inspection (VT): Examination of the overlay surface for defects such as porosity, spatter, slag inclusion, and lack of fusion.
Magnetic particle testing (MT): Detection of surface and near-surface cracks in the overlay and dilution zone.
Ultrasonic testing (UT): Evaluation of bond strength between the base metal and overlay layer using contact UT or phased array UT (PAUT).
Hardness testing: Verification of hardness profile across the overlay thickness to ensure proper dilution control.
Chemical analysis: Spot checking of overlay composition to confirm compliance with the specified grade (304, 316, etc.).
Intergranular corrosion testing: Verification of sensitization resistance in the dilution zone per GB/T 4334.

Engineering Practice Integration

The study presents a case study of a 316L strip cladding application on 16MnR base plate for a chemical reactor. The base plate dimensions were 20 mm (thickness) × 3000 mm (width) × 6000 mm (length), with a 5 mm 316L overlay layer applied on one side. The fabrication process included:

Base plate preparation: Surface cleaning to remove scale, rust, and contamination. The surface was ground to a smooth finish to ensure good bond strength.
Preheating: The base plate was preheated to 150 °C to reduce residual stress and prevent hydrogen-induced cracking.
Strip cladding: Two passes of 316L wire were applied using the optimized process parameters (700 A, 32 V, 450 mm/min). The dilution rate was measured at 25% on the first pass and 15% on the second pass.
Post-weld heat treatment: The clad plate was solution treated at 1080 °C for 30 minutes with water quenching to dissolve chromium carbides and restore full corrosion resistance in the dilution zone.
Inspection: UT bond strength testing confirmed a bond strength of 98% (exceeding the 95% acceptance criterion). Intergranular corrosion testing showed no sensitization in the dilution zone.

The resulting clad plate achieved a corrosion rate of less than 0.05 mm/year in a 10% H₂SO₄ solution at 60 °C, compared to 2.5 mm/year for the unclad 16MnR base plate. This demonstrates the effectiveness of the strip cladding process in providing corrosion protection for chemical processing equipment.

Study Insights and Implications

The most significant insight from this literature is that submerged arc strip cladding is a highly efficient and reliable method for producing stainless steel clad plate, provided that process parameters are carefully controlled to minimize dilution and ensure full bond strength. The key challenge is balancing deposition efficiency with dilution control; higher deposition rates often come at the cost of increased dilution, which may compromise corrosion resistance.

For engineers involved in pressure vessel fabrication, the practical implications are clear: strip cladding should be considered as the preferred method for producing large-area clad plate due to its high productivity and consistent quality. However, the dilution zone must be carefully managed through process optimization and post-weld heat treatment. The acceptance criteria for bond strength and dilution rate should be established based on the specific service conditions and applicable standards.

The literature also highlights the importance of flux selection in controlling dilution and preventing defects. A low-silica, low-fluorine flux is essential for minimizing chromium loss and maintaining the corrosion resistance of the overlay layer. The flux recovery and reuse system should be designed to minimize contamination and maintain consistent flux properties throughout the fabrication process.

In conclusion, this literature provides a comprehensive guide to the submerged arc strip cladding process, covering process parameter optimization, dilution control, quality inspection, and engineering application. The key message is that strip cladding is a mature and reliable technology for producing high-quality clad plate, but its success depends on careful process control and rigorous quality assurance. Engineers who implement these recommendations can achieve significant improvements in fabrication efficiency and product quality for pressure vessel and chemical equipment applications.