A Closer Look at Threaded Fastener Failure and How to Prevent It

Don't let threaded fastener failures derail your projects. Click here to discover its causes and learn expert tips to prevent it.

Last Updated on February 12, 2024 by Ossian Muscad

Threaded fasteners are pivotal in countless mechanical connections, yet their critical role is often overlooked until failure occurs. Catastrophic malfunctions, costly downtime, and safety hazards can all stem from the failure of these seemingly small components. As we delve deeper into the world of threaded fastener failure, we will uncover the many underlying causes and explore preventive measures that can be taken. In this exploration, it becomes clear that understanding the forces at play and the material science behind fasteners is key to ensuring the longevity and reliability of mechanical systems worldwide.

 

What is Threaded Fastener Failure?

Threaded fastener failure occurs when the item does not perform as intended, which can be caused by various factors, including over-tightening, under-tightening, corrosion, fatigue, and material defects. Over-tightening can lead to excessive stress and potential yielding of the material, while under-tightening might result in inadequate clamping force, allowing parts to move or separate.

Corrosion weakens fasteners through chemical reactions with their environment, and fatigue can cause cracks to form over time due to cyclic loading. Material defects, including impurities or inconsistent properties, can also compromise the integrity of a fastener. Avoiding these common issues is critical to maintaining the integrity of the fastener and the entire mechanical assembly it secures.

 

Causes of Threaded Fastener Failure

Several catalysts cause threaded fastener failures. Knowing and understanding each cause is important for mitigating future failures and anticipating when this problem occurs with existing bolts in your machinery.

Vibration

Vibration is by far the leading cause of threaded fastener failure. Loose bolts that are not secured tightly are subject to wiggling and rattling over time. The constant movement causes the threads to become misaligned and stressed. This gradual wear on threads creates even larger gaps that result in damage and eventual failure.

Manufacturing Error

Manufacturing Error is another leading cause of threaded fastener failure. This usually happens during the threading process when the bolt isn’t cut correctly. As a result, the threads are either too weak or not cut evenly. This error is often difficult to spot and goes unnoticed until it’s too late.

Poor Installation

Poor installation is an operator error that leads to threaded fastener failure. This usually happens when the bolt is not installed correctly or overtightened. Both cases put too much stress on the threads, which can cause them to warp or snap.

Mismatched Hardware

Mismatched hardware happens when a nut that is too big or weak complies with the bolt. This often happens when the maintenance team is in a hurry to fix machinery and doesn’t have the right tools or hardware. As a result, they make do with whatever they have, which can cause threaded fastener failure.

Embrittlement

Embrittlement is a type of threaded fastener failure that’s caused by corrosion. When bolts are constantly exposed to moisture and other corrosive elements, it can cause the metal to weaken and break down. This threaded fastener failure is often difficult to spot because it happens gradually over time.

Any of these catalysts is more than enough to cause threaded fastener failure over a long period. Unfortunately, one problem paves the way for another to arise, which can rapidly expedite the time for your machinery to succumb to failure.

 

Preventing Threaded Fastener Failure

To mitigate the risk of threaded fastener failure, adopting a proactive approach towards maintenance and assembly is essential. Implementing proper installation techniques, using the correct materials, and conducting regular inspections are fundamental to maintaining fastener integrity. By investing time in understanding the principles of fastener use and care, we can significantly extend the lifespan of machinery and prevent untimely malfunctions. The following are proven strategies for preventing threaded fastener failure:

Thread locking

Thread locking is an effective method used to prevent threaded fasteners from loosening due to vibration and other dynamic forces. This can be achieved through various means, such as using chemical thread lockers, nylon patches, safety wires, or lock washers. Chemical thread lockers are adhesives applied to the threads before assembly, which cure to form a bond between the male and female threads.

When pre-applied to the fastener, nylon patches create a tight and strong mating to the threads. Safety wires secure bolts in place mechanically, preventing them from rotating. Lastly, lock washers provide tension during fastening, making the joint resistant to rotation. Each of these thread-locking techniques offers advantages and can be selected based on the specific application and environmental conditions the fastener will encounter.

Mechanical Locking

Mechanical locking devices, such as locknuts, locking washers, and jam nuts, are expressly designed to prevent fasteners from loosening under vibration and other dynamic loads. These devices can physically prevent the fastener from turning and backing out, thus maintaining the requisite tension in the joint. Locknuts often incorporate a feature that grips the mating thread of the bolt, providing resistance to vibration loosening.

On the other hand, locking washers create a load between the bolt head or nut and the assembly, often employing a cam, wedge, knurl, or serration feature to resist motion. In applications with severe vibration, jam nuts, which are thinner than standard nuts and tightened against the main nut, can be effective. This ‘double nutting’ method is a traditional and reliable mechanical locking technique that distributes the load across two nuts, significantly reducing the risk of loosening. Employing these devices is a widely recognized method for enhancing the durability and safety of bolted connections.

Undercutting

Undercutting is a technique that involves creating a notch or groove at the root of the fastener’s thread. This practice increases the length of the thread engagement without changing the diameter of the fastener, distributing the load more evenly across all engaged threads. Undercutting reduces the likelihood of fatigue failure by reducing the stress concentration at the first few threads near the head of the fastener, which are typically subjected to the highest load.

Furthermore, undercutting can enhance the overall performance of fasteners in critical applications by allowing a more even distribution of the axial load along the thread engagement, resulting in increased fatigue strength and improved joint reliability. It is crucial, however, that undercutting is done correctly to not compromise the strength of the fastener, making it a task that requires precise engineering and careful execution.

Thread-sealing Tape

Thread-sealing tape, also known as PTFE (Polytetrafluoroethylene) tape, plumber’s tape, or Teflon tape, is a common solution for sealing pipe threads to prevent leaks in plumbing and piping systems. This non-sticky tape is wrapped around the threads of pipes before they are connected, creating a fill for the small gaps that could allow liquid or gas to pass through.

The tape is highly resistant to various chemicals and can withstand various temperatures, making it suitable for applications involving water, natural gas, steam, and certain chemicals. Applying thread-sealing tape requires precision to ensure a secure fit and full coverage of the thread without impeding the threading action.

 

Frequently Asked Questions (FAQs)

Q1: What causes threaded fasteners to lose tension over time, even without visible damage?

Threaded fasteners can lose tension over time due to a phenomenon called ‘relaxation.’ As the materials undergo micro-level yieldings under the compressive force, they can slightly deform, lessening the clamping force initially provided by the fastener.

Q2: How can extreme temperatures affect threaded fasteners?

Extreme temperatures can cause materials to expand or contract, which affects the tension in fasteners. Heat can lead to thermal expansion and, over repeated heating and cooling cycles, might result in loosening of fasteners. On the other hand, extreme cold can make certain materials brittle, which increases the risk of cracking under stress.

Q3: Can electrical currents contribute to threaded fastener failures?

Yes, electrical currents can contribute to threaded fastener failures through a process called ‘electrolytic corrosion,’ which can occur when fasteners are exposed to electrical currents in the presence of an electrolyte, such as water, leading to accelerated corrosion and potential failure.

Q4: Is there a way to determine when a fastener is nearing the end of its service life before it fails?

Regular inspections that look for signs of wear, corrosion, or damage can indicate when a fastener may be nearing the end of its service life. Additionally, monitoring the torque and tension of the fasteners over time can provide insights into their current state and future reliability.

Q5: What are the consequences of reusing fasteners in critical applications?

Reusing fasteners in critical applications can be hazardous. It compromises their integrity because they may have undergone stretching or deformation that diminishes their clamping force and could lead to unpredictable failures.

Q6: How does the environment play a role in threaded fastener failure?

Environmental factors such as humidity, temperature fluctuations, pollutants, and exposure to corrosive substances like saltwater can all expedite the deterioration of fasteners through processes like rusting or corrosion, which weakens the fasteners and potentially leads to failure.

 

Prevent Threaded Fastener Failure with DATAMYTE

DATAMYTE is a quality management platform with low-code capabilities. Our Digital Clipboard, in particular, is a low-code workflow automation software that features a workflow, checklist, and smart form builder. This tool lets you build custom workflows to manage inspection plans, compliance forms, and more. It also allows you to automate alerts when certain criteria are met or inspections fail, helping you identify potential issues before they result in costly failures.

DATAMYTE also lets you conduct layered process audits, a high-frequency evaluation of critical process steps, focusing on areas with the highest failure risk or non-compliance. Conducting LPA with DATAMYTE lets you effectively identify and correct potential defects before they become major quality issues.

With DATAMYTE, you have an all-in-one solution for preventing threaded fastener failures and ensuring the overall quality of your production processes. Don’t wait for costly failures; start using DATAMYTE today and save time, money, and resources in the long run. Book a demo now to learn more.

 

Conclusion

The integrity of threaded fasteners is crucial for the reliability and safety of various applications, from industrial machinery to household items. Understanding the factors leading to fastener failure is essential for prevention and maintenance. Through strategies such as proper selection, installation, and ongoing inspection, the longevity and performance of these components can be significantly enhanced. 

Avoidance of common issues such as stress concentration, thermal expansion, and corrosive environments will reduce the potential for untimely failure. Staying informed and vigilant in the management of threaded fasteners will ultimately secure both operational efficiency and safety standards across numerous sectors.

 

 

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