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.
How long is a burst test on an expansion joint?
July 31, 1990
Tag: faq
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.
What is squirm pressure?
Squirm pressure is the pressure at which in-plane instability occurs.
How do define a hydro-test pressure based on design pressure?
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, the hydro-test pressure will be ASME B31.4,B31.8 1.5 x design pressure.
How do you calculate pressure thrust load?
| Pressure thrust load is calculated by finding the area of the mean diameter of the bellows and multiplying it by the design pressure. |
Why do rubber expansion bellows fail?
Rubber bellows can crack if they are over-pressurized or placed in a harsh environment.
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.
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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.
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Improper installation and insufficient protection.
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During and after installation.
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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.
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Improper anchoring, guiding and supporting of the system.
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Anchor failure in service.
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Bellows corrosion, both internal and external.
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System over-pressure (in-service or hydrotest). Bellows vibration (mechanical or flow-induced resulting in high cycle fatigue).
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Excessive bellows deflection (axial, lateral, angular deflections greater than design values).
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Torsion.
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Bellows erosion.
- Packing of particulate matter in the bellows convolutions which inhibits proper movement of the bellows.
