CLADDING TECHNOLOGY SHANXI CO., LTDQuality Control of High-Efficiency Automatic Cladding Composite Steel Plate - A Technical Study Note
Literature Overview
The manufacture of composite steel plates through high-efficiency automatic cladding is a critical process in the production of corrosion-resistant and wear-resistant structural components for the chemical, petrochemical, nuclear, and energy industries. The composite plate consists of a structural base plate, typically a carbon steel or low-alloy steel, and a cladding layer of stainless steel, nickel alloy, or other corrosion-resistant material. The quality of the bond between the base and the cladding layer is the primary determinant of the plate's performance and service life. This study focuses on the quality control measures required to ensure the integrity of high-efficiency automatic cladding processes, which typically employ multi-wire submerged arc welding (SAW) or electroslag welding (ESW) at high deposition rates.
Core Technical Content
High-efficiency automatic cladding processes are designed to maximize productivity while maintaining the required bond strength and cladding quality. The typical process parameters for multi-wire SAW cladding are as follows:
| Parameter | Specification |
|---|---|
| Base plate | Q345R / SA-516 Gr.70 / 16MnR |
| Cladding material | 304 / 316 / 321 / Inconel 625 |
| Welding method | Multi-wire SAW (2-4 wires) |
| Wire diameter | 1.6 mm to 2.4 mm |
| Welding current | 400 A to 800 A |
| Welding voltage | 28 V to 35 V |
| Travel speed | 200 mm/min to 500 mm/min |
| Flux type | Rutile or basic flux |
| Flux coverage | 10 mm to 15 mm |
| Preheat temperature | 100 C to 200 C |
| Interpass temperature | Below 250 C |
| Cladding thickness | 3 mm to 10 mm |
| Number of passes | 1 to 4 |
The quality control process is structured around several key checkpoints, each designed to detect potential defects before they propagate to the next stage of production. The approach follows the PDCA (Plan-Do-Check-Act) cycle, ensuring continuous improvement of the process.
Pre-Production Quality Control
Before cladding begins, the following inspections are performed:
- Base plate material verification: certificate review, chemical analysis, and mechanical property verification
- Base plate surface preparation: removal of rust, oil, paint, and scale by grinding or shot blasting to a Sa 2.5 standard
- Welding consumable verification: wire and flux certificates, moisture content testing for flux
- Welding procedure qualification (WPQR): verification that the procedure has been qualified for the specific base and cladding material combination
- Welder qualification: verification that the welder or operator is qualified for the specific process and material combination
In-Process Quality Control
During the cladding operation, the following parameters are monitored:
| Monitoring Parameter | Method | Acceptance Criteria |
|---|---|---|
| Arc voltage | Digital meter | Within +/- 2 V of setpoint |
| Welding current | Digital meter | Within +/- 10 A of setpoint |
| Travel speed | Encoder feedback | Within +/- 5 percent of setpoint |
| Wire feed speed | Encoder feedback | Within +/- 5 percent of setpoint |
| Preheat temperature | Thermocouple | 100 C to 200 C |
| Interpass temperature | Thermocouple | Below 250 C |
| Flux coverage | Visual inspection | 10 mm to 15 mm |
Any deviation from the specified parameters triggers an alarm and may require stopping the welding process for correction. The process parameters are recorded for each plate and stored in a traceability database for future reference.
Post-Production Quality Control
After cladding is complete, the following inspections are performed:
- Visual inspection (VT): 100 percent inspection of the cladding surface for undercut, porosity, cracks, and surface irregularities
- Magnetic particle testing (MT): 100 percent inspection of the cladding surface for surface and near-surface cracks
- Ultrasonic testing (UT): 100 percent inspection of the cladding-base interface for lack of fusion and delamination
- Hardness testing: verification of the hardness profile across the cladding layer and the heat-affected zone
- Bond strength testing: peel test or shear test on a sample plate to verify the bond strength meets the minimum requirement
- Chemical analysis: verification of the cladding layer composition, particularly the dilution level
- Mechanical testing: tensile testing of weld coupons to verify the mechanical properties
Defect Analysis and Countermeasures
The study identifies several common defects in high-efficiency automatic cladding and proposes countermeasures:
| Defect | Cause | Countermeasure |
|---|---|---|
| Lack of fusion | Excessive travel speed, low current, poor surface preparation | Reduce travel speed, increase current, improve surface preparation |
| Porosity | Wet flux, surface contamination, excessive arc length | Dry flux, clean surface, adjust arc length |
| Cracking | High carbon equivalent, excessive interpass temperature, hydrogen | Preheat, control interpass temperature, use low-hydrogen consumables |
| Excessive dilution | High current, low travel speed, thin base plate | Reduce current, increase travel speed, increase base plate thickness |
| Surface undercut | Excessive current, excessive travel speed | Reduce current, reduce travel speed |
| Uneven cladding thickness | Fixture misalignment, wire feed inconsistency | Calibrate fixture, verify wire feed system |
The root cause analysis of defects should follow the 5W2H methodology: What defect occurred, Where did it occur, When did it occur, Who was responsible, Why did it occur, How did it occur, and How to prevent it. This systematic approach ensures that corrective actions are targeted and effective.
Engineering Practice Integration
In the manufacture of composite plates for pressure vessels and heat exchangers, the quality control process is typically integrated into the overall fabrication quality plan. The composite plate is subject to the requirements of standards such as GB/T 150, NB/T 47002, ASME VIII Div.1, and API 934, which specify the acceptance criteria for the cladding layer and the bond strength.
The FMEA (Failure Mode and Effects Analysis) approach is applied to identify potential failure modes in the cladding process and prioritize them based on severity, occurrence, and detectability. The most critical failure modes are typically lack of fusion at the cladding-base interface and cracking in the cladding layer, both of which can lead to catastrophic failure of the pressure vessel during service.
The study emphasizes the importance of process documentation and traceability. Each plate is assigned a unique identification number, and all process parameters, inspection results, and test reports are linked to this number. This traceability is essential for quality assurance and for investigating any issues that arise during fabrication or service.
Study Insights and Reflections
The study underscores a critical principle in quality control: the most effective quality assurance is not achieved through inspection alone but through process control. The goal is to produce a conforming product on the first pass, rather than detecting and rejecting nonconforming products. This requires a deep understanding of the process parameters, the material properties, and the interrelationships between them.
One important insight is the role of dilution in determining the performance of the cladding layer. Excessive dilution can reduce the corrosion resistance of the cladding layer by introducing carbon and other alloying elements from the base material. However, zero dilution is neither achievable nor desirable, as some dilution is necessary to ensure adequate bond strength. The optimal dilution level is a balance between corrosion resistance and bond strength, and it varies with the specific application.
Another insight is the importance of surface preparation. The quality of the bond between the base and the cladding layer is directly related to the cleanliness and roughness of the base surface. A surface that is too smooth may not provide adequate mechanical interlocking, while a surface that is too rough may trap contaminants. The recommended surface roughness is Ra 6.3 to 12.5 micrometers, achieved by grinding or shot blasting.
Summary and Outlook
The quality control of high-efficiency automatic cladding composite steel plates requires a comprehensive approach that integrates pre-production verification, in-process monitoring, and post-production inspection. The key to success is the establishment of a robust process control system that ensures consistent process parameters, the implementation of rigorous inspection procedures that detect defects early, and the maintenance of comprehensive documentation and traceability records. Engineers working in this field should adopt a systematic approach to quality management, utilizing tools such as PDCA, FMEA, and 5W2H to continuously improve the process and prevent defects. The future of composite plate manufacturing lies in the integration of advanced process monitoring technologies and data-driven quality management systems that can predict and prevent defects before they occur.