Rubber expansion joints have a service life defined by environmental and application conditions. According to the Fluid Sealing Association (FSA), for a rubber expansion joint that is in critical service and is 5 or more years old a planned replacement at a scheduled outage or spare should be considered. If the service is not of a critical nature, then regular observation of the expansion joint should be planned with replacement considered after 10 years of service. Applications vary considerably and operating life can be as long as 30 years in some cases. For any operator there are some key questions:
- Do you know the current condition of your rubber expansion joints?
- How much time could they operate without any show signs of failure?
The following guide shows the most typical failures modes. It is intended to assist in determining if an expansion joint should be replaced or repaired after extended service.
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Replacement Criteria / Typical failure modes
1/ Cracking
Most typically sun cracking, or crazing, may not be serious if only the outer cover is involved and the fabric (reinforcement) is not exposed. If necessary, repair on site with rubber cement where cracks are minor.
Cracking where the fabric is exposed and torn, indicates the expansion joint should be replaced. Such cracking is usually the result of excess extension, angular or lateral movements. In these cases, the following may also be present:
- A flattening of the arch. In the next photo, it can see a flattening of the arch on an expansion joint over elongated more than 50mm. Severe displacement. Correct pipe layout and replace expansion join required.
- Cracks at the base of the arch and/or at the base of the flange. Severe damage, it must be replaced when internal reinforcing fibres are exposed.
Some of these movement induced cracks can be addressed by installing suitable tie-rods.
2/ Blisters-Deformation-Ply Separation
Some blisters or deformations, when on the external portions of an expansion joint, may not affect the proper performance of the expansion joint. These blisters or deformations are cosmetic in nature and do not require repair.
If major blisters, deformations and/or ply separations exist in the tube, the expansion joint should be replaced as soon as possible.
Ply separation at the flange O.D. can sometimes be observed and is not a cause for replacement of the expansion joint.
3/ Dimensions
Any inspection should verify that the installation is correct, that there is no excessive misalignment between the flanges and that the installed face-to-face dimension is correct. Check for over-elongation, over-compression, lateral or angular misalignment.
In the next photo, an over elongation can be showed. The neutral building length was 300mm, the allowable extension was 30mm, but the expansion joint was elongated more than 50 mm. It is a severe displacement. Correct pipe layout and replace the expansion joint is case of visible cracks.
4/ Metal or Fabric Reinforcement
If the metal or Fabric reinforcement of an expansion joint is visible through the cover, the expansion joint should be replaced as soon as possible. Additionally, if any external metal reinforcement is exhibiting signs of fatigue or wear, the expansion joint should be replaced as soon as possible.
5/ Rubber Deterioration
If the joint feels soft, gummy, spongy or porous, the rubber is decomposing due to chemical incompatibly with the medium. Plan to replace the expansion joint as soon as possible.
6/ Leakage
If leakage or weeping is occurring from any surface of the expansion joint, except where flanges meet, replace the joint immediately. If leakage occurs between the mating flange and expansion joint flange, tighten all bolts.
In the next picture it can see the fluid medium is leaking through flange spine, due to a pore in the rubber tube. Critical Damage. Replace immediately.
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