The Myth of Reusing Instrumentation Fittings Ferrules

Understanding the Risks of Reusing Ferrules in Instrumentation Tube Fittings

In instrumentation systems, tube fittings rely on ferrules to ensure a secure, leak-tight seal. Ferrules function by deforming and biting into the tubing’s outer diameter when the fitting nut is tightened. This controlled deformation, or cold working, is critical to achieving a reliable seal. However, this same deformation permanently alters the shape and structure of the ferrule, meaning it cannot be returned to its original form once used.

Reusing ferrules poses significant risks due to their compromised integrity after initial compression. Once released from the tubing, ferrules no longer maintain their original dimensions, reducing their effectiveness in subsequent installations. This deformation substantially increases the likelihood of leaks, jeopardizing system reliability and potentially causing equipment damage or downtime. Additionally, microscopic fractures can occur during the initial tightening process, invisible to the naked eye but capable of expanding with repeated use, further undermining the fitting's sealing capabilities.

From a performance and safety perspective, the minor cost savings of reusing ferrules are vastly outweighed by the risks introduced. Instrumentation systems typically operate under stringent conditions, requiring components with uncompromised integrity to maintain reliability and accuracy. Employing previously used, deformed ferrules directly contradicts these critical reliability standards and introduces unnecessary vulnerabilities into the system.

Best practices strongly recommend using new ferrules for each assembly of instrumentation tube fittings. Additionally, cutting back the tubing to reveal a fresh, clean surface ensures an optimal seal. This practice eliminates previous compression marks, corrosion, and mechanical wear, thereby extending the lifespan of the instrumentation system and maintaining its intended high performance and safety standards.

Sources

-Anand Srivastava & Sheikh Rafik Manihar Ahmed, i-manager’s Journal on Future Engineering and Technology, Vol. 12, No. 1, 2016.

-Parker Hannifin, Metallurgy Makes or Breaks Tube Fittings, 2007.

-Musa Mihsein & Mike D. Seymour, Journal of Engineering Design, Vol. 10, No. 4, 1999.

-Valin Corporation, Developments in Stainless Steel Instrumentation Tube Fittings.