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The Fluid Systems Engineering and Management Blog

by Swagelok Northern California

FAQ: Are these parts interchangeable?

by Jeff Hopkins, on 5/31/18 8:30 AM

We're often asked how interchangeable and intermixable a Swagelok component or assembly is with another brand. Here's the 411.

"Data that Swagelok collects from field surveys show that intermixing and interchanging has terrible results—leak rates are through the roof (19%) on the fittings field tested, for example."

- Jason Burns, Swagelok Northern California

What is interchange and intermix?

  • Interchange - A tube fitting manufactured by one company that has been installed on a piece of tubing is then disassembled, and the tubing, nut and ferrules from that installed fitting is reassembled into the body of another manufacturer.
  • Intermix - Tube fitting components, which include the nuts, ferrules, and bodies, from two or more fitting manufacturers that are mixed together and then assembled to make a complete fitting.

It is dangerous to mix materials or fitting components from various manufacturers—including but not limited to tubing, ferrules, nuts, and fitting bodies.

Leak-tight seals that will withstand high pressure, vibration, vacuum, and temperature changes depend on close tolerances and consistent, exacting quality control in conjunction with good design principles. The critical interaction of precision parts is essential for reliability and safety. A video below illustrates this.

Components of other manufacturers may look like Swagelok tube fitting components, but they cannot be manufactured in accordance with Swagelok engineering standards, nor do they benefit from innovations in design and manufacture defined by 36 active Swagelok tube fitting patents issued since 1989.

Facts from the Journal of Engineering Design

Musa Mihseiin and Mike D. Seymour published in the Journal of Engineering Design, Vol.10, No.4. the findings of independent research examining "the effects of intermixing the component parts of twin ferrule tube fittings manufactured by four different companies." It concludes that intermix/interchange can lead to system issues, leakage, and safety concerns.

Here is the paper's summary (bolding added):

"This paper presents the findings of an independent study carried out to examine the effects of intermixing the component parts of twin ferrule tube fittings manufactured by four different companies. Experimental tests and finite element analysis has shown that the swaging and sealing mechanisms of fittings are different despite seeing geometric similarities. It was evident that no two companies produced components to the same dimensional or metallurgical specification and that pressure testing alone should not be used as the only means of validation.

"The ERA plots of intermixed fittings show that a form of sealing occurred in some combinations which could lead to acceptance. However,it was not until further engineering assessment was made could it be seen that the sealing methods were not as originally designed and therefore a high risk factor must be applied. In addition to the design safety factors being compromised any intended sealing mechanism either became superfluous or over-stressed. Other components were stressed to levels in some unintended way and often were found to impede the movement of other parts and acting as a conduit or fatigue failure."

Here are the authors' conclusions:

  1. Divergent range of sealing surfaces are created due to design, construction, and torque value differences
  2. Different sealing surface incompatibilities exist due to geometry, tolerances, and metallurgic properties
  3. Intermixing components as described in this study could lead to compromised function
  4. Undesirable stress concentration can be caused by intermixing leading to fatigue failure
  5. Series of movement measurements provide strong evidence that intermixing components can create ineffective sealing surfaces resulting from different swaging mechanisms, material hardness, and tolerance variations
  6. Pressure testing should not be used as the only means for compatibility verification. FEA plots of intermixed fittings demonstrate that a “form of sealing” occurs, however a “high risk factor must be applied to such combinations.”

Extreme testing video

Years ago, Swagelok tube fittings were put through a severe thermal shock test at an oil refinery facility in Ohio. The classic film is still great at illustrating the temperatures pressures and stresses our tube fitting connections withstand with absolutely no leakage.

Helping you choose

We can take some of the sting out of replacement component searches by identifying product alternatives and highlighting any savings such as reduced purchase cost, maintenance, and downtime. To talk with our engineering team or ask a technical question, start here:

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We perform under pressure

Your fluid systems can't fail—and they can't leak. That's why Swagelok Northern California offers mission critical solutions for the petrochem, semi, power, and oil and gas industries around the Bay Area and into NW Nevada. We manufacture and assemble reliable, customizable components that get the job done. Contact our team today to learn about custom solutions for your plant or refinery.

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