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If the expansion joint is not tied the pressure thrust will act on the turbine exhaust nozzle and the adjacent piping.

Single expansionjoint
Tied Single Metallic Bellows

The pressure rating is the maximum allowable pressure to be used for that particular expansion joint. Each pressure rating is specified on a case-by-case basis per expansion joint.

16" Diameter Externally Pressurized Expansion Joints for an Oil Refinery
Expansion Joints Designed for a Pressure Rating of 150 PSIG at 176°F

It is the force generated due to the pressure inside the expansion joint. Pressure thrust is calculated by multiplying the area of the mean bellows diameter by the pressure.

Bull 02 a
Bellows “PA” (pressure x area) load

What is end thrust?

It is the force generated due to the pressure inside the expansion joint. Pressure thrust is calculated by multiplying the area of the mean bellows diameter by the pressure.

Bull 02 a
Bellows “PA” (pressure x area) load
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Squirm pressure is the pressure at which in-plane instability occurs.

Bellows squirm example
Example of a Bellows Squirm
Bellows undergoing a hydro-test, with pressure defined by the design pressure
Bellows undergoing a hydro-test pressure

How does US Bellows define a hydro-test pressure based on design pressure?

When determining the pressure for hydrostatic testing of your expansion joints, the most important aspect is the applicable design codes. Normally, the ASME SEC VIII Div.1 general hydro-test pressure will be 1.3 x design pressure, but if you are testing for ASME B31.1, B31.3,B31.4, it will be 1.5 x design pressure. 

That being said, there are many other considerations that will determine the test pressure, such as:

  • Test Duration
  • Temperature
  • End conditions of the assemblies
  • Special cases based on the customer’s situation

Be sure to discuss with our engineers so that we can correctly test your bellows and expansion joints.

How do define a hydro-test pressure based on design pressure?

Bellows undergoing a hydro-test, with pressure defined by the design pressure
Bellows undergoing a hydro-test pressure

How does US Bellows define a hydro-test pressure based on design pressure?

When determining the pressure for hydrostatic testing of your expansion joints, the most important aspect is the applicable design codes. Normally, the ASME SEC VIII Div.1 general hydro-test pressure will be 1.3 x design pressure, but if you are testing for ASME B31.1, B31.3,B31.4, it will be 1.5 x design pressure. 

That being said, there are many other considerations that will determine the test pressure, such as:

  • Test Duration
  • Temperature
  • End conditions of the assemblies
  • Special cases based on the customer’s situation

Be sure to discuss with our engineers so that we can correctly test your bellows and expansion joints.

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Pressure thrust load is calculated by finding the area of the mean diameter of the bellows and multiplying it by the design pressure.

Expansion joints failure is caused by corrosion, erosion, cyclic fatigue or thermal creep at elevated temperatures.

Inst maint over pressure
Expansion Joint Failure

Rubber bellows can crack if they are over-pressurized or placed in a harsh environment.

113108v1a1
Neoprene Rubber Expansion Joint

Failures can occur for many reasons, but experience has shown that certain causes of failure fall into fairly distinct categories.

  • Shipping and handling damage. Examples: Denting or gouging of bellows from being struck by hard objects (tools, chain falls, forklifts, adjacent structures, etc.); improper stacking for shipping or storage; insufficient protection from weather or other adverse environmental conditions.

  • Improper installation and insufficient protection.

  • During and after installation.

  • Examples: Joints with internal liners installed in the reverse direction with respect to flow; installing an expansion joint in a location other than as prescribed by the installation drawings; premature removal of shipping devices; springing of bellows to make up for piping misalignment; insufficient protection from mechanical damage due to work in the surrounding area; insufficient protection of bellows during nearby welding operations and failure to remove shipping devices before placing system in operation.

  • Improper anchoring, guiding and supporting of the system.

  • Anchor failure in service.

  • Bellows corrosion, both internal and external.

  • System over-pressure (in-service or hydrotest). Bellows vibration (mechanical or flow-induced resulting in high cycle fatigue).

  • Excessive bellows deflection (axial, lateral, angular deflections greater than design values).

  • Torsion.

  • Bellows erosion.

  • Packing of particulate matter in the bellows convolutions which inhibits proper movement of the bellows.
Number22
Failed Competitor Expansion Joint

 

Why do expansion joints fail?

Failures can occur for many reasons, but experience has shown that certain causes of failure fall into fairly distinct categories.

  • Shipping and handling damage. Examples: Denting or gouging of bellows from being struck by hard objects (tools, chain falls, forklifts, adjacent structures, etc.); improper stacking for shipping or storage; insufficient protection from weather or other adverse environmental conditions.

  • Improper installation and insufficient protection.

  • During and after installation.

  • Examples: Joints with internal liners installed in the reverse direction with respect to flow; installing an expansion joint in a location other than as prescribed by the installation drawings; premature removal of shipping devices; springing of bellows to make up for piping misalignment; insufficient protection from mechanical damage due to work in the surrounding area; insufficient protection of bellows during nearby welding operations and failure to remove shipping devices before placing system in operation.

  • Improper anchoring, guiding and supporting of the system.

  • Anchor failure in service.

  • Bellows corrosion, both internal and external.

  • System over-pressure (in-service or hydrotest). Bellows vibration (mechanical or flow-induced resulting in high cycle fatigue).

  • Excessive bellows deflection (axial, lateral, angular deflections greater than design values).

  • Torsion.

  • Bellows erosion.

  • Packing of particulate matter in the bellows convolutions which inhibits proper movement of the bellows.
Number22
Failed Competitor Expansion Joint

 

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The failure mode of bellows could be any of a variety of things including erosion, corrosion, cyclic fatigue or thermal creep at elevated temperatures.

Failed expansion joint
Universal Metallic Expansion Joint from Competitor with Squirm Damage

What is the failure mode of bellows?

The failure mode of bellows could be any of a variety of things including erosion, corrosion, cyclic fatigue or thermal creep at elevated temperatures.

Failed expansion joint
Universal Metallic Expansion Joint from Competitor with Squirm Damage
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Regarding the operating temperature, we design metal pipe expansion joints up to 2000° F with refractory and 1000° F to 1500° F without refractory.

92501c1
Metallic Expansion Joint

Toroidals  can be used but not often. Most exchanges use normal thin-wall expansion joints or thick-wall expansion joints fabricated from flanged and flued heads.

72 inch thick wall expansion joint for a sulfuric acid plant
72″ inch thick wall pipe expansion joint

The weight of the units is self-supporting but the additional weight of the piping, elbows etc. in the field will not be supported by the expansion joint.

55 inch double gimbal expansion joint for a reactor overhead line
Gimbal pipe expansion joint

Yes, this is one of the expansion joint functions

No, it is the total of the spring rates of all three bellows.

36 pressure balanced elbow expansion joints
36″ Pressure Balanced Elbow Pipe Expansion Joint

 

The number of expansion joints used in a pipe depends on the length of the pipe, the pressure, the temperature, and the size. Upon knowing these design conditions, we can inform you of the number of expansion joints the pipeline requires.

An expansion joint is used to absorb dimensional changes, such as those caused by thermal expansion or contraction of a pipeline, duct, or vessel.

113108v2a1
High Temperature Fabric Expansion Joint Designed for an Exhaust Duct

The expansion joint used for fuel oil and fuel gas applications depends on the movement and design conditions of the particular application within the plant.

100875b1
Fabric Expansion Joints

The spring rate is equal to the spring rate of both flow bellows plus the spring rate of the balancing bellows.

Pic 001 1
Elbow Pressure Balanced Pipe Expansion Joint

Expansion joints are needed to absorb thermal movement when piping flexibility will not solve the problem.

110901a1
92″ Double Hinged Reinforced Expansion Joint for Water Service