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Why does your equipment always loosen? What is the cost of choosing the wrong bolt grade?
In the fields of industrial equipment, building structures, heavy machinery, etc., bolt loosening is a common but dangerous problem. It not only causes equipment vibration and increased noise, but may also cause connection failure, safety accidents, and even millions of repair losses.
The root of the problem often lies in choosing the wrong bolt grade. This article will reveal:
- The real reason behind bolt loosening
- The three serious consequences of choosing the wrong bolt grade
- How to correctly choose high-strength bolts?
- Why do your bolts always loosen?
- Insufficient strength, insufficient tensile/shear resistance
When ordinary bolts (such as 4.8 grade) are used in high-load equipment, they are easily deformed due to excessive stress, resulting in loss of preload and eventually loosening.
Case: A mine conveyor belt uses 4.8 grade bolts. After 3 months, it loosened due to vibration, causing the belt to deviate, and the loss of production suspension and maintenance exceeded $50,000.
- Thread mismatch, poor anti-loosening performance
Coarse thread (UNC) is easy to loosen in high-frequency vibration environment, while fine thread (UNF) or anti-loosening thread (such as Spirax) can provide better locking effect.
Case: A car factory used ordinary bolts to fix the engine bracket, and the bolts fell off due to vibration, triggering a recall.
- Improper surface treatment and unstable friction coefficient
Unoptimized bolts are prone to rust in high temperature, humid or corrosive environments, resulting in torque attenuation and reduced preload.
Case: An offshore wind power project used ordinary galvanized bolts, and the tower connection failed due to salt spray corrosion one year later.
- The three major costs of choosing the wrong bolt grade
- Safety hazards: bolt failure = disaster risk
In key structures such as bridges, wind power, and pressure vessels, bolt failure may cause collapse, explosion, or casualties.
Real event: In 2019, a petrochemical plant suffered a leak due to bolt breakage, with direct losses exceeding $2 million.
- Soaring maintenance costs
Equipment downtime + bolt replacement + labor costs are often 5-10 times more expensive than directly using high-strength bolts.
Data: A manufacturing company's annual maintenance costs increased by $120,000 due to the use of low-grade bolts.
- Damage to brand reputation
Customer complaints due to bolt problems may affect long-term cooperation and even cause legal disputes.
- How to choose the bolt grade correctly?
- Select strength grade according to load
| Application Scenario | Recommended level | tensile strength |
| General mechanical equipment | 8.8 | ≥800 MPa |
| Wind power, bridges, heavy machinery | 10.9 | ≥1000 MPa |
| Aerospace, precision equipment | 12.9 | ≥1200 MPa |
- Match environmental requirements
High vibration environment → Choose fine thread + nylon locking nut
Corrosive environment → Choose Dacromet or stainless steel A4-80
High temperature environment → Choose alloy steel (such as 42CrMo)
- Find professional suppliers to avoid fakes
Require material report (MTC), salt spray test report, ISO 9001 certification.
Tips: Use magnet test, real 10.9 grade bolts are usually weakly magnetic (alloy steel).
- 4. Summary: Don't let bolts become the weakest link!
✔ Low-strength bolts = invisible bombs, which may cause safety and financial risks.
✔ Correct selection can extend equipment life and reduce maintenance costs.
✔ Choose a reliable supplier to ensure that the material and process meet the standards.
Is your equipment using the right bolts? Welcome to consult our engineering team for free to get customized solutions!
