Zhuojin Pipe Fitting Co., LtdSpark Discharge Atomic Emission Spectroscopy for Compositional Analysis of Strip Electrode Surfacing Deposited Metal
Literature Overview
This study published in Metallurgical Analysis (2018, Vol. 38, No. 11) by Liu Manyu and colleagues from Harbin Weil Welding Co., Ltd. and Harweld Huatong (Changzhou) Welding Industry Co., Ltd. addresses a critical quality control challenge in strip electrode surfacing (SES) production. The work investigates the application of spark discharge atomic emission spectroscopy (SD-AES) for determining the chemical composition of seven elements—carbon, silicon, manganese, sulfur, phosphorus, chromium, and nickel—in deposited metal produced via the strip electrode surfacing process.
Core Technical Problem and Motivation
In industrial surfacing operations, particularly for wear-resistant and corrosion-resistant overlay applications on piping and pressure equipment, rapid and accurate compositional analysis of deposited metal is essential for process control and quality assurance. SD-AES offers speed and non-destructive testing advantages, but the study identifies a fundamental problem: when standard reference materials of dissimilar composition and microstructure are used as type standardization samples, significant analytical deviations arise. This discrepancy stems from differences in physical properties, crystal structure, and matrix effects between the calibration standard and the actual test specimen.
Experimental Methodology and Key Findings
Light Source Parameter Optimization
The researchers systematically optimized three critical light source parameters for SD-AES measurement:
| Parameter | Optimized Value | Rationale |
|---|---|---|
| Flush time | 5 s | Removes surface oxide layer and contaminants |
| Pre-burn time | 6 s | Stabilizes arc and removes volatile elements |
| Integration time | 7 s | Ensures sufficient signal accumulation for trace elements |
These parameters represent a balanced compromise between measurement speed and analytical accuracy, particularly important for low-concentration elements such as sulfur and phosphorus.
Type Standardization Method Comparison
The study compared two standardization approaches:
| Standardization Method | Calibration Material | Result Quality |
|---|---|---|
| Method 1: Stainless steel standard | ZBGS003 (stainless steel reference) | Large deviations, especially for Cr |
| Method 2: Self-made control samples | SES deposited metal samples | Results consistent with wet chemical analysis |
The most significant finding is that using stainless steel standard ZBGS003 for calibration produced substantial errors when analyzing SES deposited metal, with chromium showing the most pronounced deviation. This occurs because the spectral line intensity ratios differ markedly between austenitic stainless steel matrices and the typical hypereutectoid or martensitic matrices found in SES deposits. The self-made control sample approach, where calibration curves are established using actual SES deposited metal of known composition verified by wet chemistry, yielded results in good agreement with reference chemical analysis.
Engineering Practice Implications
Quality Control Protocol Development
For production environments involving strip electrode surfacing, this research provides clear guidance on analytical methodology:
- Standard reference materials of dissimilar composition should not be used for type standardization when the matrix effects are significant.
- Self-made control samples matching the expected composition range of production deposits should be prepared and certified through wet chemical analysis.
- The optimized light source parameters (5 s flush, 6 s pre-burn, 7 s integration) provide a reproducible measurement protocol suitable for routine quality inspection.
Connection to Piping and Fitting Industry
In the context of pipe and fitting manufacturing, SES is widely used for:
- Adding wear-resistant overlays to valve bodies and ball valves
- Corrosion-resistant cladding on piping components
- Repair and refurbishment of worn piping equipment
The accuracy of compositional analysis directly impacts the selection of appropriate surfacing materials for specific service conditions. For example, in sour service (H2S-containing environments), the carbon and chromium content of the deposit must be precisely controlled to avoid intergranular corrosion or hydrogen-induced cracking.
Key Questions and Reflections
The study raises an important question about the economic trade-off between analytical accuracy and cost. Preparing self-made control samples requires certified reference materials, careful sample preparation, and wet chemical verification—resources that may not be available in all production facilities. However, the consequences of inaccurate compositional data include non-conforming products, field failures, and potential safety incidents in pressure piping systems.
Another reflection concerns the applicability of this methodology to other surfacing processes. The matrix effect problem identified here likely extends to hardfacing with submerged arc welding (SAW), flux-cored arc welding (FCAW), and plasma transfer arc (PTA) processes. The principle that calibration standards should match the test material in physical and structural characteristics is universal in spectroscopic analysis.
Study Insights and Implications
This work demonstrates that analytical methodology in welding quality control must be adapted to the specific process being monitored. The one-size-fits-all approach of using generic stainless steel standards for all surfacing deposits is technically unsound. Engineers responsible for welding procedure qualification and production quality assurance should mandate process-specific calibration protocols when SD-AES is employed for deposited metal analysis. The research also underscores the importance of understanding spectroscopic matrix effects—a topic often overlooked in practical welding quality control but fundamental to obtaining reliable analytical data.