Abstract
With the rapid growth of the solar industry, the solar hanger bolt has become an essential component of PV mounting systems, especially for pitched roof installations, where it secures the racking to structural beams and resists wind, snow, and dead loads. The choice of material has a direct impact on system safety, durability, and lifecycle cost. Stainless steel 304 and 316 are the two most widely used materials, but they exhibit different performance characteristics under various conditions. This article compares their characteristics, highlights practical application scenarios, and provides clear selection guidelines for PV developers, installers, and EPC contractors.
I. Introduction
Every detail in a solar installation contributes to long-term performance and safety. As a key fastener in roof-mounted systems, the solar hanger bolt must deliver both mechanical strength and corrosion resistance. A poor material choice could result in premature corrosion, loosening, or even structural failure, leading to system downtime or safety risks.
Stainless steel is the preferred material for hanger bolts due to its strength and durability. Among the various grades, SUS304 and SUS316 stainless steels are the most common. Understanding their differences is critical to making an informed choice.
II. Stainless Steel Basic
The defining feature of stainless steel is the passive film that forms on its surface. This thin chromium oxide layer isolates the metal from corrosive agents and can self-repair when damaged in oxygen-rich environments.
For solar hanger bolts, which are exposed to rain, condensation, and pollutants, this self-protection ability is crucial.
III. SUS304: The Cost-Effective Choice
A. Composition
Contains ~18% chromium and ~8% nickel, offering balanced performance.
B. Mechanical Properties
Tensile strength: 515–620 MPa; yield strength: 205–310 MPa. Good ductility and workability make it suitable for large-scale bolt production.
C. Corrosion Resistance
Performs well in freshwater and atmospheric conditions but is prone to pitting and crevice corrosion in chloride environments (salt spray, acid rain).
D. Cost Advantage
Lower initial and processing costs make it attractive for budget-conscious projects.
E. Applications
- Inland, dry, non-polluted regions;
- Residential or commercial pitched roof PV systems with 20–25 years expected service life.
IV. SUS316: The High-Protection Choice
A. Composition
Contains 16–18% chromium, 10–14% nickel, and 2–3% molybdenum. The addition of molybdenum significantly enhances resistance to chloride-induced corrosion.
B. Mechanical Properties
Comparable to SUS304, but with slightly improved high-temperature strength and creep resistance.
C. Corrosion Resistance
Excellent resistance to harsh environments, including:
- Coastal areas with salt spray exposure;
- Island or tropical climates with high humidity;
- Industrial zones with acidic pollutants;
- Frequent condensation or standing moisture conditions.
D. Cost and ROI
Although more expensive initially, SUS316 often proves more economical in the long run due to reduced maintenance, fewer replacements, and improved system reliability.
E. Applications
- Coastal residential and commercial PV rooftops;
- Offshore or island installations;
- PV projects near industrial plants;
- Large-scale power plants require maximum reliability.
V. Key Comparison: SUS304 vs SUS316
| Property | SUS304 | SUS316 |
|---|---|---|
| Main Alloying Elements | Chromium (~18%), Nickel (~8%) | Chromium (~16–18%), Nickel (~10–14%), Molybdenum (~2–3%) |
| Chloride Resistance | Moderate, prone to pitting/crevice corrosion | Excellent, strong resistance to pitting/crevice corrosion |
| General Corrosion Resistance | Good for atmosphere and freshwater | Superior, suitable for harsher conditions |
| Mechanical Properties | Strong, ductile, versatile | Similar to SUS304, slightly better at high temps |
| Initial Cost | Lower | Higher |
| Fabrication/Weldability | Excellent | Excellent |
| Typical Applications | Inland, mild environments | Coastal, humid, polluted environments |
This table highlights the essential performance differences and provides a clear reference for selection.
VI. Practical Application & Selection Guidelines
1. Environment-Based Selection
- Inland dry regions require SUS304, which is both sufficient and economical.
- Coastal, high-humidity, or industrial areas → SUS316 is essential for long-term safety.
2. Project Lifecycle
- Short-term or budget-limited projects → SUS304 provides a cost-effective solution.
- Long-term projects (≥25 years lifespan) → SUS316 ensures reliability and lower lifecycle costs.
3. Rooftop PV Mounting Systems
In pitched roof installations, solar hanger bolts anchor mounting rails to timber rafters or steel purlins.
- For standard inland rooftops → SUS304 is suitable.
- For coastal or industrial rooftops → SUS316 prevents premature corrosion and ensures system stability.
VII. Conclusion
There is no absolute “better” material—only the more suitable one.
- SUS304: A cost-effective solution for mild environments.
- SUS316: Superior protection in harsh, chloride-rich, or polluted conditions.
For developers, EPCs, and installers, the choice between SUS304 and SUS316 should be based on environmental conditions, project lifespan, and budget considerations, ensuring the safety, durability, and cost-effectiveness of PV mounting systems.
Company Information
Suzhou Bilateral Import & Export Co., Ltd. is a professional supplier specializing in solar mounting systems and fastener solutions. Our flagship products include roof solar mounting systems and accessories such as solar hanger bolts, middle clamps, and side clamps. The product portfolio covers complete solar mounting systems and a wide range of solar accessories, widely applied in residential, commercial, and utility-scale PV projects.
With strict material selection standards and advanced manufacturing processes, our products are trusted by customers worldwide and have been exported to Europe, Southeast Asia, and the Middle East.
For more information, please visit: www.szbolts.com
