"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 amount of variations on service conditions that exist at any given facility. However, one of the best available tools to aid in your investigation is careful examination of the installed gasket at the time of leakage and the joint system itself.
If you are able to get to the connection before someone has already disassembled it, it is helpful to make a mark on the gasket, the flange and the location of the leak. It is also helpful to observe the condition of the fasteners, as these can be good indicators of the internal/external environments and the overall gasket compatibility with the conditions. When disassembling the flange, follow established on-site safety protocols, make reference to how the first nut loosens and recognize the remaining bolts may be affected once this first bolt is removed.
Once the joint is disassembled, try to remove the gasket in one piece or in as large pieces as possible. Some of the more common bolted flange connection leakage mechanisms relating to a chemical attack are described below, along with some remediation strategies to prevent recurrence of the leakage situation.
Chemical attack
Example: Gasket is badly corroded at all media contact surfaces. Metal and semi-metallic gaskets are easier to assess for the onset of a chemical attack than soft non-metallic gaskets. Metal corrosion that occurs in a general sense is referred to as general attack corrosion. This will often be evident by virtue of the exposed metal surfaces changing color or becoming chalky. This condition is not always a concern in the short term and can be easily remediated by choosing a more compatible metal for the service media. Typically, the metal components of the gasket will match the metallurgy of the piping system.
For non-metallic gaskets, a chemical attack can often resemble mechanical damage. A chemical attack typically manifests as radial splits, starting on the gasket ID where it was exposed to the media, along with some degradation of the rubber binder used in the gasket material. It is best to work with your gasket supplier or preferred manufacturer to get advice on material compatibility, regardless of the general data published by most manufacturers.
Example: Metal gasket surface is pitted, flakey and missing material. When your metal gasket appears to show signs of material loss or significant pitting, you may be experiencing galvanic corrosion. This occurs when two dissimilar metals are touching each other in the presence of a corrosive electrolyte. The two metals form a bond, with one becoming an anode and the other a cathode. The anode is the sacrificial component and is where you will see material loss. The Fluid Sealing Association provides excellent information on galvanic corrosion relating to gasket applications in its “Gasket Handbook,” and users should reference this as a basis for remediation.
Understanding the bigger picture
It is important to recognize a bolted flange connection leaks more often than 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. In part two of this how-to series of articles, we will investigate mechanical modes of attack and put together a more complete picture of failure modes.
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