EXPANSION JOINTS / BELLOWS / COMPENSATORS DESIGN TERMINOLOGY

Bellows is a thin walled flexible element that allows growth in a piping system while containing the pressure and medium flowing through it. It Bellows is a flexible seal. The convoluted portion of the expansion joint is designed to flex when the thermal movements occur in the piping system. The convoluted element must be strong enough circumferentially to withstand the internal pressure of the system, yet responsive enough to flex. The number of convolutions depends upon the amount of movement the bellows must accommodate or the force that must be used to accomplish this deflection. These convolutions allow movement in Axial, Lateral, Angular and Torsional directions. It can also isolate the system vibrations.

Axial Movement: This is the most common type of bellows deflection and is simply the dimensional change of the bellows along its longitudinal axis. This axial movement is typically a shortening of the bellows or COMPRESSION. This compression of the bellows would occur as the piping heats up and expands. Another type of axial movement in a bellows is the elongation of the bellows or EXTENSION. Extension would occur for example in a cryogenic system in which the piping would contract as the temperature drops.

Lateral Movement: This type of bellows deflection is the relative displacement of the bellows ends perpendicular to its longitudinal axis. This type of displacement occurs with the bellows ends remaining parallel to each other and can occur in more than one plane. If lateral deflection does occur in more than one plane, a resultant is calculated and used in the bellows evaluation. This movement in multiple planes should be evaluated with respect to cycle life and hardware orientation.
PARALLEL OFFSET and TRANSVERSE are other common terms for lateral deflection.

Angular Movement: This type of bellows deflection is the displacement of the longitudinal axis of the bellows into a circular arc about its center and at its midpoint. This deflection may also occur in a number of planes and should be properly evaluated with respect to cycle life and hardware orientation. ROTATIONAL MOVEMENT is another term for angular deflection or rotation. This is not to be confused with torsional rotation.

Torsional Movement: This type of bellows deflection is the twisting of one end of the bellows with respect to the other end, about the bellows centerline. Due to the extremely high shear stresses produced by this type of deflection, it is usually advisable to provide the piping system or expansion joint with restraints or hardware that will relieve the bellows of this torsional load.

CONCURRENT: The movements shown in this catalog are based on any one type of movement occurring alone. This movement condition is known as non-concurrent or rated movements. In most expansion joint applications there can be a combination of movements that occur simultaneously or concurrently. This could be an expansion joint that is subjected to axial movement in combination with a lateral offset. In this case, the selection of the proper expansion joint can be best determined by the bellows designer who can evaluate the effect of these movements and provide the optimum bellows design.

VIBRATION: Metallic bellows can be designed to accommodate system vibration as a result of pumps, fans, or other rotating equipment. If the rotational speeds or frequencies of the equipment are specified, the bellows designer can evaluate the bellows and assure that it does not have a resonant or harmonic frequency that is in a range that will cause premature bellows failure.

DESIGN: Our technical team use the latest computer aided tools to provide fast proposal turn around and the most efficient use of space and materials. Every BELOFLEX Expansion Joint is designed and manufactured in strict accordance with the latest edition of EJMA code of design and confirm to the pressure and temperature standards of various international codes. The EJMA standards are accepted internationally and give known parameters of design, production and application of Expansion Joints. Detailed calculations to validate design in accordance with latest editions of EJMA standards are available on request. A design specification is prepared for each Expansion Joint application. Each bellows has a unique working pressure, spring rate, and cycle life that are entirely dependent on its geometry and material.

SPRING RATE: Bellows behave like springs in a piping system. When the bellows are moved they resist the movement the same as a spring would.

CYCLE LIFE: This is also known as Fatigue life, Design life, Bellows life, Cycles to failure, or Design oscillations. One Expansion joint life cycle is defined as a complete movement from the initial position in the piping system to the operating position and back to the initial position. All other components of Expansion Joints such as weld ends, internal sleeves, flanges, anchors, hinges etc. are defined in accordance with the required working and design conditions.