You are here: Home » News » Fastener Knowledge » What Extra Bolt Requirements for Farm Mounting Systems?

What Extra Bolt Requirements for Farm Mounting Systems?

Author: Site Editor Publish Time: 2025-06-11 Origin: Site

Additional Requirements for Bolts in Agricultural Photovoltaic Mounting Systems: Pesticide Corrosion Resistance and Anti-Loosening Vibration Measures

In agricultural photovoltaic (PV) systems, bolts face unique environmental and mechanical challenges beyond conventional structural applications. The integration of solar panels with farmland operations introduces specific demands, particularly in resisting pesticide corrosion and withstanding vibration-induced loosening. These requirements stem from the harsh agricultural environment, where chemicals, moisture, and dynamic loads from machinery or natural forces create a complex service condition for fastening components.

Pesticide Corrosion Resistance: Material and Coating Solutions

Chemical Resistance Demands in Agricultural Environments

Agricultural PV 支架 (PV mounting frames) are frequently exposed to a variety of pesticides, herbicides, and fertilizers, which often contain aggressive chemical components such as chlorides, sulfates, and organic acids. For example, glyphosate-based herbicides and ammonium nitrate fertilizers can create corrosive microenvironments when in contact with metal surfaces, especially under humid conditions. Unlike traditional industrial or civil structures, agricultural PV bolts must endure prolonged exposure to these chemicals, which can cause uniform corrosion, pitting, or even stress corrosion cracking if inappropriate materials are used.

Advanced Material Selection

Stainless Steel Grades for Chemical Resistance: Austenitic stainless steels like 316/316L (UNS S31600/S31603) are preferred due to their high chromium, nickel, and molybdenum content, which provides excellent resistance to chloride-induced corrosion and organic acids. In highly corrosive areas (e.g., citrus orchards using copper-based fungicides), duplex stainless steels (e.g., 2205) may be specified for their superior strength and corrosion resistance.

Special Alloy Applications: In extreme cases, bolts made from alloys like Hastelloy C-276 or (titanium alloys) can be used, though their high cost typically restricts application to critical connections in severely corrosive environments.

Protective Coatings Beyond Standard Treatments

High-Performance Electrodeposited Coatings: Zinc-nickel (Zn-Ni) or zinc-cobalt (Zn-Co) alloys offer 3-5 times the corrosion resistance of conventional galvanized coatings, with salt spray test results exceeding 1,000 hours without red rust. These coatings form a dense passive layer that resists pesticide penetration.

Polymer-Based Coating Systems: Organic coatings like PTFE (Teflon), epoxy-phenolic blends, or zinc-rich epoxies provide a chemical barrier. For example, a two-part epoxy coating with a zinc primer and topcoat can withstand prolonged exposure to agricultural chemicals while maintaining adhesion to the substrate.

Thermal Spraying Technologies: Metallic coatings applied via thermal spraying (e.g., zinc, aluminum, or stainless steel) create a thick, pore-free layer that acts as both a barrier and a sacrificial anode, ideal for bolts in direct contact with soil or irrigation water.

Anti-Loosening and Vibration Resistance: Mechanical Design and Installation Strategies

Dynamic Load Challenges in Agricultural Settings

Agricultural PV systems are subjected to unique vibration sources:

Machinery Induced: Tractors, harvesters, and sprayers operating near PV arrays generate low-frequency, high-amplitude vibrations that can loosen bolts over time.

Environmental Factors: Wind-induced oscillations of PV panels, especially at resonance frequencies, create cyclic loading on connections. Thermal expansion and contraction from daily temperature fluctuations (often exceeding 40°C in agricultural regions) also induce dynamic stresses.

Advanced Anti-Loosening Technologies

Mechanical Locking Devices:

Nylon-Insert Lock Nuts (Prevailing Torque Nuts): Nylon inserts create frictional resistance to prevent rotation, effective in moderate vibration environments. Examples include ASTM F436 Type IA nuts.

Wedge-Lock Washers (e.g., Belleville Washers): These conical springs maintain clamping force by converting axial relaxation into radial tension, ideal for high-vibration applications.

Locking Washers with Serrations: Spring washers with sharp teeth bite into the mating surface to resist rotational movement, though care must be taken to avoid damaging coating integrity.

Thread Locking Compounds:

Medium-Strength Threadlockers (e.g., Loctite 243): Anaerobic adhesives fill thread gaps, curing in the absence of air to create a secure bond that is removable with tools.

High-Strength Threadlockers (e.g., Loctite 272): Suitable for permanent connections, these compounds provide higher temperature resistance (up to 150°C) and require heat for disassembly.

Specialized Thread Designs:

Non-Return Threads (e.g., Spiralock): A modified thread profile with a 30° wedge ramp eliminates clearance between the bolt and nut, converting vibrational forces into axial clamping force.

Self-Locking Threads: Rolled threads with a reduced pitch diameter create interference fit, generating frictional resistance without additional components.

Installation and Maintenance Best Practices

Torque Control and Verification:

Use calibrated torque wrenches to apply specified preloads, ensuring consistent clamping force. For agricultural PV bolts, torque values should account for coating friction coefficients (e.g., 0.12-0.15 for PTFE-coated bolts vs. 0.20-0.25 for plain steel).

Implement torque marking (stripe or dot) to visually inspect for loosening during routine maintenance.

Vibration-Damping Materials:

Install elastomeric washers or grommets between metal components to absorb low-frequency vibrations from agricultural machinery.

Use anti-vibration mounts for critical connections, especially where PV panels attach to supporting structures.

Periodic Inspection Protocols:

Develop a maintenance schedule to re-torque bolts after the first 100 hours of operation, then quarterly during peak agricultural activity.

Employ non-destructive testing (NDT) methods like ultrasonic thickness measurement to assess coating degradation or material loss due to corrosion.

Environmental and Operational Considerations

UV and Weather Resistance

Agricultural PV bolts must withstand prolonged ultraviolet (UV) exposure, which can degrade polymer coatings or cause embrittlement in certain materials. Specify UV-stabilized coatings (e.g., polyester topcoats over zinc primers) or materials inherently resistant to UV degradation, such as 316 stainless steel or anodized aluminum bolts.

Moisture and Corrosion Cycling

The combination of pesticide exposure and high humidity (common in irrigated fields) creates a corrosive cycle. Bolts should have a corrosion protection system that addresses both chemical resistance and moisture barrier properties. For example, a duplex system of zinc-nickel plating plus a PTFE topcoat provides dual protection against electrolyte penetration and chemical attack.

Compatibility with Agricultural Practices

Bolts must not interfere with farming operations:

Low-Profile Designs: Use countersunk or flush-head bolts to prevent snagging on harvesting equipment.

Non-Projecting Connections: Avoid protruding bolts in areas where machinery passes, reducing the risk of damage to both the bolt and the equipment.

Regulatory and Industry Standards

Adhere to specific standards for agricultural installations:

ISO 16730:2015: Covers corrosion protection for agricultural machinery components.

UL 2703: Standard for Solar Panel Mounting Systems: Includes requirements for fasteners in outdoor environments, though agricultural-specific supplements may be needed.

Local Agricultural Codes: Some regions have regulations governing chemical exposure limits for materials in food-producing areas, necessitating food-grade coatings or materials where applicable.

Case Studies and Practical Applications

Citrus Orchard PV Installation

In a Florida citrus orchard PV project, bolts connecting the (mounting frames) to concrete piers were exposed to copper sulfate-based fungicides and high humidity. The solution included:

316L stainless steel bolts with PTFE-impregnated coatings.

Wedge-lock washers combined with medium-strength threadlocker to resist vibrations from citrus harvesters.

Annual inspection and re-torque schedule during the spraying season.

Cornfield Solar Farm in the Midwest

In a cornfield PV system in Iowa, bolts faced challenges from anhydrous ammonia fertilizers and combine harvester vibrations. The specification included:

Zinc-nickel plated carbon steel bolts (8.8 grade) for cost-effectiveness with superior corrosion resistance.

Spiralock thread design on critical connections to prevent loosening from combine-induced vibrations.

Elastomeric washers at panel-clamp interfaces to dampen wind-induced oscillations.

Conclusion: Integrating Specialized Bolt Solutions for Agricultural PV Systems

Bolts in agricultural photovoltaic mounting systems must meet rigorous additional requirements beyond standard structural applications, primarily in pesticide corrosion resistance and anti-loosening vibration measures. The combination of chemical exposure from agricultural inputs and dynamic loading from machinery and environmental factors demands a holistic approach to material selection, coating technology, mechanical design, and maintenance. By implementing high-performance materials like 316 stainless steel, advanced protective coatings such as zinc-nickel alloys, and specialized anti-loosening devices like Spiralock threads or threadlocker compounds, engineers can ensure the long-term reliability and safety of agricultural PV systems.

Failure to address these unique requirements can lead to premature bolt degradation, connection loosening, and even system collapse, risking both economic loss and agricultural operation disruptions. As agricultural PV systems continue to grow in popularity, the careful specification and maintenance of bolts will remain a critical factor in ensuring the sustainability and performance of these hybrid energy-agricultural installations.