Single-Layer Cladding Technology Research on Domestic Nickel-Based Welding Strip

Overview and Significance

Nickel-based alloy cladding is essential for pressure vessels, heat exchangers, and piping systems operating in aggressive chemical environments such as sulfuric acid, hydrochloric acid, and reducing acid media. The single-layer cladding technology using domestic nickel-based welding strips addresses a critical supply chain concern: reducing dependence on imported nickel-based welding consumables while achieving equivalent cladding performance. This study focuses on the electroslag welding (ESW) overlay process using domestic nickel-based welding strips, evaluating the metallurgical quality, mechanical properties, and corrosion resistance of the resulting cladding layer.

Process Parameters and Metallurgical Control

The single-layer ESW overlay process is characterized by a high deposition rate (10–20 kg/h), deep penetration, and minimal dilution of the base metal into the cladding layer. For single-layer cladding, the key challenge is to achieve a cladding layer thickness of 3–6 mm with adequate dilution control (typically < 30%) while maintaining sound metallurgical bonding to the base steel. The process parameters include welding current (typically 4,000–6,000 A for ESW), welding voltage (32–38 V), welding speed (300–500 mm/min), and slag composition (controlled to ensure stable slag pool and proper wetting).

Parameter	Typical Range	Impact on Cladding Quality
Welding current	4,000–6,000 A	Higher current increases dilution and penetration
Welding voltage	32–38 V	Affects arc stability and slag pool behavior
Welding speed	300–500 mm/min	Faster speed reduces dilution but may cause defects
Preheat temperature	100–200°C	Reduces thermal stress and cracking susceptibility
Interpass temperature	≤ 300°C	Critical for controlling dilution and microstructure
Cladding thickness	3–6 mm	Single-layer requirement for efficiency
Dilution ratio	< 30%	Target for maintaining corrosion resistance

The metallurgical quality of the single-layer cladding is evaluated through metallographic examination, hardness testing, and dilution analysis. The dilution ratio is determined by measuring the carbon content or chromium content in the cladding layer and comparing it with the base steel composition. A dilution ratio exceeding 30% may compromise the corrosion resistance of the cladding layer, particularly in reducing acid environments where the protective oxide film formation is critical.

Defect Analysis and Countermeasures

Common defects in single-layer nickel-based cladding include lack of fusion at the cladding-base interface, cracks (both hot cracks and cold cracks), porosity, and insufficient dilution control. The FMEA (Failure Mode and Effects Analysis) approach is valuable for systematically identifying and mitigating these defects.

Defect Type	Root Cause	Countermeasure
Lack of fusion	Insufficient heat input, poor fit-up	Increase current, improve fit-up, preheat
Hot cracks	High sulfur/phosphorus in weld metal	Use low-S/P consumables, control cooling rate
Cold cracks	Hydrogen embrittlement, high CML base steel	Increase preheat, use low-hydrogen consumables
Porosity	Moisture in flux, inadequate shielding	Dry flux, ensure proper gas shielding
High dilution	Excessive penetration, high current	Reduce current, increase speed, use backing strip

The domestic nickel-based welding strips must meet the compositional requirements of the relevant standards (such as GB/T 222, ASTM A263, or EN 10028-7) and demonstrate consistent mechanical properties and corrosion resistance. The key alloying elements (Ni, Cr, Mo, W, Cu) must be controlled within tight tolerances to ensure the cladding layer achieves the required corrosion resistance in the target service environment.

Engineering Practice and Standards Compliance

The single-layer cladding technology must comply with applicable pressure vessel codes, including GB/T 150, ASME VIII Div.1, and NB/T 47002. The welding procedure qualification (WPQ) must be performed in accordance with NB/T 47014 or ASME IX, with qualification parameters that cover the production range of variables. The performance qualification requires demonstration of adequate dilution control, mechanical properties, and corrosion resistance of the cladding layer.

For hydrogenation reactors and other high-temperature pressure vessels, the cladding layer must also demonstrate resistance to hydrogen-induced cracking (HIC) and sulfide stress corrosion (SSC), as specified in NACE MR0175/ISO 15156. The domestic nickel-based welding strips must be evaluated for these properties, and the cladding procedure must be qualified for the specific service conditions.

Summary

The single-layer cladding technology using domestic nickel-based welding strips offers a cost-effective and supply-chain-secure solution for corrosion-resistant pressure vessel fabrication. The technology requires careful control of process parameters, metallurgical quality, and compliance with applicable codes and standards. The successful implementation of this technology depends on the consistent quality of the domestic welding strips, the skill of the welding operators, and the rigorous quality assurance procedures that ensure the cladding layer meets the required performance specifications for the intended service environment.