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4 Types of Bellows Metallic Expansion Joints

Mar. 21, 2022

Standard bellows have many engineering functions. In various industrial piping applications, bellows metallic expansion joints are used to compensate for movements in piping systems. The bellows metallic joints prevent vibrations, expansions, and any other changes from damaging pipes that cover long distances.

This article presents to you different types of bellows metallic expansion joints and their respective uses.



What are custom expansion joints?

Metallic expansion joints are elastic vessels, which are compressible under pressure or extensible under a vacuum. The release of the vacuum or pressure causes the metallic bellow to return to its original shape if the bellow’s material doesn’t get stressed beyond the yield strength. There are four basic metallic expansion joints, which are categorized based on the manufacturing technology used.


1. Machined Bellows

Machined bellows are ground or turned from forged rings, tubing, and bar stock of materials used to make other kinds of metal bellows. Low modulus, high-strength titanium alloys and heat-treatable, high endurance, and high-strength steel are often used to make machined bellows. Machined bellows are custom bellows made to have a high spring rate to hold pressure as high as 82.73 MPa.

Machined Bellows: What are bellows used for?
These bellows find use in industrial applications that need a high spring rate and a high-pressure thrust.


2. Convoluted or Formed Bellows

Formed metal bellows are manufactured from reworked tubes made made by deep drawing. Different processes are utilized during production, which can include hydro-forming, punch forming, cold forming, and roll forming. These types of bellows can be built from different metallic materials at an affordable cost, if mass-produced. Formed bellows have high-pressure stability and capabilities

Convoluted or Formed Bellows: What are bellows used for?
Formed bellows find widespread use in petrochemical refineries, boiler plants, cement plants, thermal plants, and steel plants.


3. Diaphragm or Welded Bellows

Welded bellows have welded convolutions, which get built from shaped diaphragms that get welded at the outer and inner diameters of the bellow’s cylindrical shape. The width of such bellows is set based on the stamped diaphragm’s diameter. The available stamping equipment determines the sizes of such bellows, and they often range from 12 to 300 mm.

Common types of diaphragm bellows include concave, convex, cantilever, and nesting welded bellows. These bellows get made from titanium, stainless steel, and other material of high strength.

Diaphragm or Welded Bellows: What are bellows used for?
Welded or diaphragm bellows are used in accumulators, pressure sensing, rotary shaft seals, mechanical seals, and valve stem seals.


4. Deposited Bellows

Deposited bellows are formed through metal deposition on an aluminum mandrel, which is later dissolved to leave the bellow behind. These bellows are manufactured through two chemical processes, which can include electrode deposited or chemical deposited methods. The two approaches can produce any shape of a bellow. Chemically-deposited bellows often get shaped with a diameter ranging between 1.524 to 177.8 mm and a thickness ranging between 0.00762 to 0.0127 mm.

Electroplated or electro-deposited bellows are often made from a nickel-cobalt alloy or nickel. Their diameter sizes range from 1.6 to 31.75 mm, and the wall thickness takes at least 0.1524 mm. These bellows are often thin-walled, and they can get made into miniature special-shaped bellows.

Deposited Bellows: What are bellows used for?
Deposited bellows find widespread applications in sensors, electrical applications, and in areas where low spring rate functions and ultra-high vacuums are necessary.


Further Uses

A metallic bellow expansion joint eases vibrations, expansions, and any other movements that can damage pipe systems. The bellow’s joints can be fashioned from varying materials that suit the application and its environment. For instance, bellows metallic expansion joints used in marine environments should have materials whose properties can resist corrosion from marine salts.

The ideal material in such cases would be marine-grade stainless steel alloys, which have Molybdenum. This element with a melting point of 4,748 degrees Fahrenheit and the atomic symbol of 42 is durable and corrosion-resistant. Depending on the industrial application of your metallic bellows expansion joints, you should choose your metal material composition with caution to get more exceptional durability and strength.


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