We do not air test fabric expansion joints; all welds are liquid penetrant tested.
What acceptance criteria do you use for air testing the fabric expansion joints?
July 31, 1990
Tag: faq
Why should we do a dye-penetrant test?
Dye-penetrant tests should be performed in order to check the integrity of the welds. At U.S. Bellows, all bellows undergo a dye-penetrant examination before being shipped to the customer.
What are the quality tests that are conducted on expansion joints?
At U.S. Bellows, we perform a variety of tests:
- Burst Testing – The objective of the burst test is to determine the ultimate pressure resistance. Primarily conducted on bellows. Normally, hydraulic pressure is slowly increased until failure occurs.
- Dye Penetration Testing – Liquid dye is used to locate leaks or cracks in the bellows.
- Hydro Testing – Bellows are pressurized for 30 minutes to locate leaks or cracks.
Burst Testing
How do you service test an expansion joint?
Expansion joints are maintenance-free. They can only be tested if the expansion joint is supplied with 2-ply testable bellows using vacuum or air pressure testing.
How do you detect a crack in a fatigue testing machine?
Cracks on a fatigue testing machine are detected by the loss of internal pressure that is shown pressure gauge on the machine.
What is the difference between pneumatic testing and helium testing?
For pneumatic testing, air is used as the medium for testing and for helium testing they use helium, and the cost for helium is much higher.
How long is a burst test on an expansion joint?
A burst test is performed under controlled conditions and pressure is applied over a period of one to two hours using the necessary safety precautions for all personnel involved.
What is blotting in a dye-penetrant test?
Blotting on a dye-penetrant test typically indicates a crack in the weld. Therefore, the crack would be repaired and the test performed once again.
What is the threshold pressure limitations of a fabric expansion joint?
July 30, 1990
| Fabric Expansion Joints can withstand up to 3 PSIG (pounds per square inch gauge) or 100″ of water (H₂O) column (In pressure). If the pressure exceeds this amount, it is best to use a metallic expansion joint. |
Does the expansion joint still work if the balancing side pressure is higher than the inline side?
The pressure is equal on both sides for a pressure 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 transmitted to adjacent equipment.
What is the pressure rating for an expansion joint?
The pressure rating is the maximum allowable pressure that the particular expansion joint can absorb. This is determined on a case-by-case basis.
What does pressure balance mean?
Pressure balance joints balance the pressure thrust forces inside of the expansion joint tie rods.
How do you attach a high pressure joint in a piping system?
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 distance of 14 pipe diameters away from the first guide. During installation, the expansion joint should be either welded or flanged into the piping system.
If a simple bellows is designed without limit rods (for operating cases), under a hydro test, do you recommend adding limit rods?
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.
What is the highest pressure that an expansion joint can take?
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.
Where does the pressure thrust act in a single bellows turbine exhaust application?
If the expansion joint is not tied the pressure thrust will act on the turbine exhaust nozzle and the adjacent piping.
What are the pressure ratings specified in expansion 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.
