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Categories - Frequently Asked Questions (FAQ)

Category Articles
How do you calculate pressure thrust load?
Added on Thu, Feb 10, 2011
Pressure thrust load is calculated by finding the area of the mean diameter of the bellows and multiplying it by the design pressure. Read More
How do define a hydro-test pressure based on design pressure?
Added on Wed, Aug 14, 2013
Hydro-test pressure & holding times vary for different design codes. For example, the ASME SEC VIII Div.1 general hydro-test pressure will be 1.3 x design pressure (minor factors may vary for this equation as well) and for piping design codes,... Read More
What is squirm pressure?
Added on Wed, Jun 29, 2011
Squirm pressure is the pressure at which in-plane instability occurs. Example of a Bellows Squirm Read More
What is end thrust?
Added on Tue, Oct 16, 2012
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.   Bellows "PA" (pressure x area) load Read More
What are the pressure ratings specified in expansion bellows?
Added on Wed, Jul 6, 2011
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. Expansion Joints Designed for a Pressure Rating of 150 PSIG at... Read More
Where does the pressure thrust act in a single bellows turbine exhaust application?
Added on Sat, Dec 10, 2011
If the expansion joint is not tied the pressure thrust will act on the turbine exhaust nozzle and the adjacent piping. Tied Single Metallic Bellows Read More
Why do bellows squirm under pressure?
Added on Thu, Feb 10, 2011
Bellows squirm because they have surpassed the critical design pressure limit. This can occur in small diameter bellows with a large number of convolutions. Example of Bellows Squirm Read More
What is the pressure rating for an expansion joint?
Added on Wed, Jul 6, 2011
The pressure rating is the maximum allowable pressure that the particular expansion joint can absorb. This is determined on a case-by-case basis. Expansion Joint Burst Testing In Order to Determine Ultimate Pressure Resistance Read More
What is the highest pressure that an expansion joint can take?
Added on Thu, Feb 10, 2011
The pressure rating an expansion joint can take depends upon pipe size and temperature. Standard units from 3 inches to 24 inches are suitable for 300 PSIG. (pounds per square inch) Higher pressures can be accommodated on a case by case basis. ... Read More
If a simple bellows is designed without limit rods (for operating cases), under a hydro test, do you recommend adding limit rods?
Added on Mon, Jun 18, 2012
Yes, if they are testing just the expansion joint or if they are testing when installed, they have to make sure that the pipe line is anchored or have limit rods added to the expansion joint to absorb the pressure thrust. Single Metallic... Read More
How do you attach a high pressure joint in a piping system?
Added on Wed, Jun 29, 2011
In an axial piping system, the expansion joint should be located as close as possible to a main anchor. The first pipe guide should be located at a distance of 4 pipe diameters away from the expansion joint. The second guide should be located a... Read More
What does pressure balance mean?
Added on Thu, Nov 3, 2011
Pressure balance joints balance the pressure thrust forces inside of the expansion joint tie rods. Elbow Pressure Balanced Expansion Joint Read More
What pressure do you recommend the bellows are tested to?
Added on Thu, Nov 3, 2011
We recommend that the bellows be tested to 1.5 times the design pressure. Burst Testing Read More
Does the expansion joint still work if the balancing side pressure is higher than the inline side?
Added on Thu, Nov 3, 2011
The pressure is equal on both sides for apressure balanced expansion joint. If the pressure difference is minor, it would not be a problem, but if the pressure thrust is high, then an imbalance of forces would occur and could result in forces being... Read More
What is the threshold pressure limitations of a fabric expansion joint?
Added on Fri, May 9, 2014
Fabric Expansion Joints can withstand up to 3 PSIG (pounds per square inch gauge) or 100" H20 column (In pressure). If the pressure exceeds this amount, it is best to use a metallic expansion joint.  Read More

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