Top 5 Mistakes When Installing Bolts in Metal Structures
How to Avoid Critical Failures in the Assembly of Industrial Fasteners
In metal structures—ranging from solar supports and agri-food frameworks to industrial anchoring systems—the quality of the bolt is just as important as its proper installation. A poorly executed fastening can lead to anything from minor misalignments to the complete failure of a structure. Below, we analyze the most common installation mistakes and how to prevent them through technical standards and applicable regulations.
Applying Incorrect Torque
Common Technical Error: Applying torque “by eye” or using uncalibrated tools. This can result in insufficient preload (leading to loosening) or excessive preload (causing fatigue failure or thread overload).
Typical Consequences
- Loss of Preload
- Progressive loosening due to vibration (risk of structural failure)
- Accelerated thread wear
Technical Recommendations:
- Use calibrated torque wrenches and apply the torque values recommended by ISO standards or the manufacturer's specifications
- For class 8.8 bolts (e.g., M12), the recommended torque generally ranges from 70 to 100 Nm, depending on the friction coefficient. This range varies based on whether the thread is lubricated (friction coefficient μ = 0.10) or dry (μ = 0.14–0.16). It may also vary depending on the type of lubricant or coating used. In any case, it's essential to consider the thread pitch (standard or fine), thread engagement length, and the material of the joint.
- Include reference torque tables based on assembly conditions (dry/lubricated, zinc-nickel, zinc-plated, galvanized, etc.).
- Implement torque control systems (batch testing, assembly torque logging).
Installing Without Proper Washers
Common Technical Error: Omitting the washer or using a generic type without considering load distribution, resistance to loosening, or proper washer sizing.
Associated Risks:
- Damage to the protective coating of the structural profile.
- Hole ovalization due to concentrated pressure.
- Risk of premature loosening.
- Plate deformation.
- Loss of preload.
Technical Recommendations:
- Use DIN 125-A washers for standard applications.
- In preloaded structures or those subject to vibration, install Nord-Lock® systems, DIN 6796 (conical), or DIN 127 (spring or lock) washers.
- Consider EN 14399-6 washers in high-responsibility structural joints.
- In aggressive environments or where galvanic corrosion may occur, insulating washers made of nylon or dielectric materials can be used.
- Choose the correct washer size.
Not Performing Regular Maintenance or Retightening
Common Technical Error: Assuming that a bolted joint requires no maintenance. Without inspection, the bolt can loosen due to vibration, thermal cycling (expansion/contraction from temperature changes), or load-induced deformations.
Real Consequences:
- Progressive loosening in solar structures due to thermal expansion and contraction.
- Loss of alignment in support systems.
- Risk of partial collapse in critical fastenings.
Technical Recommendations:
- Establish visual inspection and annual retightening protocols (or follow the manufacturer's maintenance plan).
- Implement visual safety markers (torque stripes) to facilitate inspection without disassembly.
- In critical structures, use bolts with torque-and-angle control (TA method), or even digital monitoring systems. These technologies are mainly used in industrial structures, automotive, or wind energy sectors, but they could also be applied to large-scale solar installations, even though it's not yet common practice.
Installation is just as important as the quality of the bolt.
A poorly tightened, incorrectly selected, or improperly installed bolt can compromise the entire structure—even if the fasteners are top quality. That’s why at SNK SYSTEM, we not only supply industrial fasteners with advanced coatings, but also support our clients with technical guidance, data sheets, applicable standards, and quality control.
