Maintenance engineers want to maximize the reliability, function, and efficiency of plant equipment and processes while increasing quality and productivity. Equipment failure is an unwelcome but unavoidable reality that negatively affects a facility’s production time, order fulfillment capability and workplace safety.
By looking at data on where equipment failures have historically occurred in hundreds of plants over a number of years, engineers can identify specific areas where failure is most likely to happen and schedule maintenance activities based on these predictions. Through the planned and selective application of sealants, coatings, and adhesives, manufacturers can protect equipment and facilities from wear, damage and corrosion, extending service life, reducing incidents of catastrophic failure and saving millions of dollars in unscheduled downtime costs each year.
This article lists five of the most common equipment and facility failures, and explains what can be done through preventive maintenance to anticipate their occurrence or limit their severity.
1. Vibrational loosening
Vibration, torque, shock, fatigue failure, thermal expansion and contraction – all of these outside forces can cause threaded fasteners like screws and bolts to loosen over time. The result of such failures can range from minor annoyances such as equipment noise to catastrophic failures. For example, on the EQ-4B Global Hawk, one of the U.S. military’s most advanced and expensive drones, screws holding a critical part that controlled movement of the wings weren’t tight enough and shook loose during a mission over Afghanistan. Within 3 minutes of the fasteners’ loosening, the $72.8 million drone crashed into the remote desert, unrecoverable.
While typical fastener failures do not result in such dramatic and devastating loss, the problem can be permanently and inexpensively fixed. Two very different strategies can counteract fastener loosening – mechanical locking methods and chemical threadlocking systems, also called machinery adhesives. But one method is much less costly and more reliable than the other.
While mechanical locking devices can help resist loosening, they cannot reliably prevent loosening caused by side sliding motion. These devices must be sized appropriately for each specific fastener, resulting in large and costly parts inventories. No locking device seals threads, which leaves assemblies vulnerable to rust and corrosion.
Threadlocking or machinery adhesives are a reliable and inexpensive way to ensure that a threaded assembly will remain locked and leak proof for its entire service life. These single-component anaerobic adhesives are applied to the threads of a bolt as a liquid, stick or tape. The adhesive fills the grooves of the threads and cures to a hard thermoset plastic when exposed to active metal ions in the absence of air. Machinery adhesives lock threaded parts together, ensuring that mating parts will ultimately act as one conjoined unit that resists failure and delivers the greatest possible reliability.
Threadlockers fill voids 100 percent to lock the threads and maintain consistent clamp load over time. Prior to cure, these adhesives lubricate the assembly to reduce friction and torque load during fastener tightening (Figure 1). Post-cure, threadlockers seal the assembly to prevent corrosion and seizure, and ensure that disassembly is consistent and predictable.
2. Air and hydraulic leaks from threaded fittings
Air and fluid leaks in threaded pipe systems are often caused by vibration or constant pressure changes. These leaks are costly and can result in a multitude of maintenance issues including equipment downtime, safety hazards, time required for cleanup of large spills, and waste disposal costs.
To give an idea of the cost of fluid leaks, one drop of hydraulic fluid dripping out of a system every 10 seconds equates to the loss of 40 gallons of fluid per year at a cost of approximately $200 per year. A single air leak through a 1/16-inch opening results in more than 278,000 cubic feet of air lost per month or 3.3 million cubic feet per year at a cost of just shy of $1000 per year.
Depending on the type of equipment, leaks can occur from more than one place – drain plugs, oiler nipples, fittings – wherever there is air space between threads (Figure 2). Leaks occur due to a number of factors. For example: the approximate metal-to-metal contact of pipe threads is just 15 percent, which allows air and fluid to pass through open spaces; threads can be damaged by wear or improper assembly; temperature changes lead to thermal expansion and contraction that results in spaces between components.
Thread sealants can reduce or eliminate leaks by forming a protective barrier that moisture, air, gas and oil cannot penetrate. These sealants create an instant seal and will not evaporate or dry up. Like threadlockers, these anaerobic adhesives cure in the absence of air when exposed to metal ions. The sealant will never evaporate or dry up, facilitates assembly by lubricating the threads, and delivers an instant, universal seal on all types of fittings.