Why We Need Exhaust Gasket and How to Select It?
The exhaust gasket seals the exhaust manifold to the cylinder head. On the V6 and V8 engines, there are two exhaust manifolds, so two manifold gaskets are required. The exhaust manifold gasket seals the connection between the manifold and the cylinder head. This prevents exhaust gases from escaping from the connection and ensures that all exhaust gases flow through the catalytic converter for treatment. Flange and ring gaskets seal other connections in the exhaust system, such as between the exhaust pipe and the exhaust manifold.
Metal gaskets are made of soft iron, mild steel, stainless steel, Monel alloy and inconel. These gaskets are also known as ring gaskets or RTJ gaskets.
Metal gaskets are used for high pressure grade flanges, typically above 900 grade, and can also be used in high temperature environments.
When we use metal gaskets, high tension bolted connections are required. They are very strong and the highest cost.
The most common materials used for these gaskets are graphite, rubber, Teflon, Teflon and compressed non-asbestos fibers (CNAF). These gaskets are also known as soft gaskets. It can be full-face or inner bolt round type. Non-metallic gaskets can be easily compressed by low tension bolts.
These types of gaskets are used for low pressure class flanges such as Class 150 and 300 and can also be used at low temperatures, but graphite gaskets can be used at temperatures up to 500 degrees Celsius.
Rubber and elastomer gaskets are not used in hydrocarbon service, but are used in utility lines.
Why use gaskets?
Leaks in flange joints can lead to product and energy loss. No plant operator or car owner wants to emit more exhaust fumes and consume more gasoline. Gaskets help achieve a reliable seal to prevent flange joint leaks.
The type of gasket used in a given fluid service depends on parameters such as
Temperature - The gasket material must withstand the entire design temperature range of the fluid it handles.
Pressure - The gasket material must withstand the entire design pressure range of the fluid it is handling.
Corrosion Resistance - The gasket material should not corrode when in contact with the fluid it is handling or when exposed to the environment.
Fluid Type - If installed in a line that handles more than one fluid type, the gasket material should be able to handle different types of fluids.
Robustness - The gasket must be able to withstand all movements that may occur due to temperature and pressure changes.
Cost - A cheap and unreliable gasket should not be used at the same time, as it should not be expensive.
Selection of gaskets
Impermeability - the gasket should not be perforated by the fluid being sealed.
Compressibility - the gasket should compress into a defect on the flange sealing surface to create an initial seal.
Stress relaxation - the gasket should not exhibit significant flow (creep) when subjected to load and temperature.
Elasticity - The flanges do actually move slightly relative to each other under the influence of cyclic temperature and pressure. The gasket should be able to compensate for this movement.
Chemical resistance - gaskets should be able to withstand chemical attack from the process media being handled. Likewise, the gasket material itself must not contaminate the process media.
Temperature resistance - The gasket should be able to withstand the maximum and minimum temperatures of the process as well as the effects of external atmospheric temperatures.
Anti-stick - the gasket must be easy to remove after use.
Corrosion resistance - the gasket shall not corrode the flange face.
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