Part 3
"My bolted flange connection continuously experiences leaks, even after trying several different product types. What can I investigate as a potential root cause?"
Performing self-diagnostics on your leaking bolted flange connection can be challenging due to the enormous variations of service conditions that exist at any given facility. In part one of this "how to" series (March, pg. 34), we looked at chemical attacks. In part two (April, pg. 47), we began to look at mechanical attacks. In this last part, we will finish looking at common mechanical attack modes.
Mechanical damage
Example: The gasket is unevenly compressed. If, after using a micrometer to measure the thickness of the postuse gasket, you notice the gasket has been unevenly compressed, you should immediately investigate the installation procedure that was used. If a formal and consistent installation procedure is not in place, it is recommended to follow the guidelines set out in ASME PCC-1 and use a cross-pattern to apply torque to the fasteners. Using this pattern will more uniformly apply stress over the entire area of the gasket and allow even compression for optimum sealing.
Example: The gasket is mechanically damaged due to overhang of the raised face or flange bore. Observation of these gaskets will quickly indicate there is a misalignment issue occurring. There are generally two causes for this situation: improper gasket dimensions for the flange or the gasket not being centered properly in the flange so the flanges themselves have become misaligned. Gasket dimensions should be reviewed to ensure they meet the requirements of the flange standard being used. During installation, care should be taken to ensure the gasket is centered as much as possible before tightening. The latter situation requires additional investigation into piping support structures and peripheral equipment that may be overloading end forces on the piping run.
Example: The gasket appears not to have been compressed. There are times when you observe the gasket almost looks like it has never been used; this should almost never be the case for a properly installed gasket. Compare the available compressive load with the recommended load for the selected gasket type. With gaskets that may be recessed into a groove, a thicker gasket may be necessary to allow for proper compression before the mating flanges touch each other. In some cases, you may also be able to reduce the gasket area, which in turn provides higher seating loads and a tighter seal over a longer period of time.
Understanding the bigger picture
It is important to recognize a bolted flange connection leaks more often than a pure gasket failure occurs. A connected system consists of mating flanges, bolts, nuts and a gasket, resulting in many combinations of inputs that can manifest as the leak you are experiencing. Ensure you specify the correct gasket design and material for the pressure, temperature, process fluid and flange arrangement, as well as industry-accepted gasket installation procedures. Contact your preferred gasket manufacturer for product assistance. Refer to the Fluid Sealing Association's new "Gasket Handbook" (first edition, 2017) and digital training material for additional details and a better understanding of your connections and how gaskets are used and interact within the system. As a system of specifically-installed components, the success of avoiding future bolted-flange connection failures significantly reduces with a greater understanding of failure mechanisms.
For more information, email info@fluidsealing.com or visit www. fluidsealing.com.