Refractory ferrules are designed to protect boiler tube inlet areas and metal tube sheets in sulfur recovery units (SRUs) used in oil refinery operations. Boiler tube inserts are also used in methane reformers and waste heat boilers (WHB). Refractory ferrules are made of materials called refractories that have high melting points. Refractories are suitable for applications requiring wear resistance, high temperature strength, electrical or thermal insulation, and other specialized characteristics. Alumina is a commonly used refractory material in boiler tube ferrule applications. Alumina’s chemical inertness and resistance to hydrogen sulfide protects the tube sheet inlets and tube sheets from hot sulfur gas corrosion. Other materials used in refractory ferrules and boiler tube inserts include silicon carbide and zircon, which may or may not be matrixed with alumina.
There are many different types of refractory ferrules. Hexhead refractory ferrules have an interlocking shape that provides stability and an interlocking fit that can eliminate or reduce the need for additional refractory mortar between ferrules. Fibrous ceramic rope and paper are used to form a seal. Hexhead ferrules are designed to fit in a tubesheet with a triangular pitch or arrangement of boiler tube openings. Square head refractory ferrules also have an interlocking shape that provides stability, and an interlocking fit that can eliminate or reduce the need for additional refractory mortar between individual ferrules. With these products, fibrous ceramic rope and paper are used to form a seal.
Square head refractory ferrules are designed to fit in a tubesheet with a square pitch or grid-like arrangement of boiler tube openings. Standard round ferrules are also available. These products feature double flanges and have a smooth circular shape with two raised ridges along the ferrule's length. Standard round ferrules require additional refractory mortar between the refractory ferrules to form a gas tight seal. The refractory cement results in a large monolithic sheet across the tubesheet face. Monolithic designs may not withstand repeated thermal cycling as well as interlocking hexhead ferrules or squarehead ferrules, however. Some refractory ferrules are manufactured with a cement-free design. This feature is important because a layer of monolithic refractory cement on the tubesheet will eventually crack under repeated heating and cooling cycles.
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