July 19, 2016
By: Chett Norton, C.E.T
Fugitive emissions are a red hot topic right now – and for good reason. With ever-increasing environmental awareness, leakage and how to prevent and reduce leaks should be on everyone’s mind. As a gasket manufacturer, it is Triangle Fluid Controls job to design, develop and educate end users on products that can help them meet upcoming low emission regulations.
Common class 150# flanges are well known as a stubborn culprit when trying to seal flanged connections – particularly 3” and 8” lines sizes. In the case of 150# flange design, an installer cannot apply enough load to the gasket due to either bolting, flange or material constraints. Another consideration is that with full face (FF) gaskets, you are trying to seal about 2-3 times the area of a ring gasket for raised-face (RF) flanges. You might ask,
“If I can’t apply more load to the gasket, how can I increase gasket load stress?”
Although it is case-by-case scenario, you have two options:
1) Reduce gasket sealing area
2) Use a controlled swell gasket material to intensify gasket stress after installation
Continue reading to determine the best option for your application.
Option 1: Reducing Gasket Area
Reducing the gasket area is extremely effective and usually one of the easiest ways to increase gasket load, when not enough load can be applied to the gasket. Remember that Pressure= Force/Area, so if we can decrease the area, the pressure (in this case the seating stress) will increase. Specifically, the Durlon RCA (Reduced Contact Area) gaskets and Durlon PTFE Step Ring gaskets are designed based on this concept. Both types of gasket are fairly unique, even though they reduce gasket area so that the gasket stress is increased. Durlon RCA type gaskets are ideal for full face (FF) flanges and FRP piping that require a tight seal, however, they cannot handle high bolt loads generally required for fugitive emissions or critical sealing applications. The skeleton of the RCA gasket resembles that of a full face (FF) one, except a large portion of the non-critical gasket area is removed for optimal sealing performance.
Durlon 9000 Step Ring gaskets are like a ring gasket, except a portion of the sealing area is reduced by machining it on a CNC lathe from one piece of material. Traditionally, these type of gaskets are manufactured by laminating two gaskets of a thinner gauge and various size together with an adhesive. Aggressive chemicals, such as sulfuric acid, can quickly eat away at the adhesive after installation, which can lead to a premature leak path. PTFE Step gaskets are commonly found in sulfuric acid plants, and applications for PTFE Step Rings include 150# raised face (RF) (Floating) Lap Joint flanges, as well as MondiTM ductile iron sulfuric acid piping.
Option 2: Controlled Swell Gasket Material
In cases where the gasket area is already minimal and cannot be changed by design, or if reducing the gasket area simply isn’t enough, selecting a controlled swell material is a great option. These types of material really shine in low load applications that involve oil and water. Once the gasket is installed, the material swells when it makes contact with oils, fuel or water, which increases gasket thickness. As the material begins to “swell”, the gasket starts to expand, exerting force in both directions, against the flanges. Imagine a Belleville washer being compressed: by design, it applies force in the opposite direction, over the entire gasket-media contact zone and not just the fastener point-load zone. In theory, this is what a controlled swell material is doing. Durlon DuraSwellTM 7760 is a prime example of how choosing a high performance sealing material can negate less than ideal gasket sealing loads and still achieve a tight low to zero emissions seal.
So, can low stress sealing applications meet fugitive emissions requirements? My answer is absolutely. As always, I recommend contacting your gasket manufacturer and providing all of the necessary application details. This will allow a specialist to recommend the proper material and installation methods to ensure the best performing sealing device for your specific needs.
Until next time, stay safe out there, and keep the fluid between the pipes!
– TFC GasketGuru
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