Why do fly ash barriers add longevity to an expansion joint?

Typically, an expansion joint creates a cavity in the duct work allowing accumulation of fly ash or dust,which can be minimized by carefully designing liner clearances and adding a fly ash barrier.

The accumulation of fly ash in expansion joints can cause substantial maintenance problems and may ultimately lead to failure of the joint. The dismantling of fabric joints, chiseling out hardened fly ash build-up, and replacing the joint fabric is a labor-intensive task that is performed semi-annually at many coal-fired plants. Severe buildup can prohibit flexibility and can tear the outer fabric from the backup bars by the sheer weight of the fly ash. Joints must often be entirely replaced at a major expense.

Fly ash barriers are designed using various materials, depending on the system temperature and media.

The fly ash barrier, which fills the entire cavity with a material less dense that fly ash, is commonly used on high temperature, dry systems or where fly ash accumulation is only a problem on one side, such as the bottom of a horizontal duct.

The two types of fly ash barriers most commonly used are an insulation pillow or wire mesh encasement of fiberglass material. However, these types of barriers are not leak-free. Although they can protect the flexible material portion of the joint, fly ash can still penetrate and harden, causing maintenance problems wich are still very labor intensive—such as removing and replacing the heavy, ash-saturated barriers.

The service life of the gas seal membrane and fly ash barrier depends on the severity of the media, materials of construction, and method of installation. Liners and fly ash barriers are designed to help prolong the life of gas seal membrane element. When the gas seal membrane is ultimately replaced, any accumulated fly ash should be removed and a new fly ash barrier installed.

 

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