Rubber expansion joints have a limited service life. According to the Fluid Sealing Association (FSA), 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 scheduled 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:

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&#; 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. SAFETECH also can help you to evaluate all the installed expansion joints current conditions: we are experts in these solutions. Do you need any help? Do not hesitate to contact us!

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 fibers 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

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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.

We know that each sector, as well as each client, requires an individual solution. From the design to the manufacture across the complete range of expansion joints, we develop specific solutions for each project. Contact us! 

How NOT to Use a Rubber Expansion Joint

What&#;s wrong with this picture?

By: Marty Rogin

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Rubber expansion joints are likely the least understood and most abused component in a piping system. They are flexible, stretchy, bendy and easily forced into lots of places despite what the installation instructions say. Most of the time, rubber joints are merely an afterthought in multimillion-dollar piping systems. Until things go awry.
The rubber joint is unmatched for vibration isolation. Properly installed, a rubber joint will greatly reduce equipment nozzle loads. Its resilience allows it to be installed in many different systems under a huge range of temperatures, pressures and media. &#;What could possibly go wrong?&#;, you may wonder.

Blame Mr. Murphy if you want, blame human nature, the Fates or the alignment of the planets. The reality of most failures is more straightforward. Most of the time, it is installation. More specifically, not following the manufacturer&#;s instructions. What follows is a rogue&#;s gallery of photos illustrating the ugly aftermath of ignored installation instructions and unforeseen operating conditions. Learn these lessons well so your piping system does not become a subject of another article.
Sometimes flexibility is a disadvantage. Why? Because it&#;s easy to compress a joint into a space that&#;s too small, which is exactly the problem here. The bead was damaged as the joint was forced into a gap between flanges, resulting in a seal failure. Spherical expansion joints rely on this bead to form a seal between flanges. If the bead is damaged, the building engineer will curse your name for eternity. Don&#;t violate the face-to-face dimensions of an expansion joint.

Pipes misaligned? Think a bendy stretchy rubber joint will fix the situation? Better think again. This joint was installed between two misaligned flanges. A typical scenario may look like this:

1.  Joint installed between two misaligned flanges.

2. Joint begins leaking at the flange-to-flange seal in a week (or month, or several months&#;).

3. Bolts tightened, leak stops. In the meantime, the rubber bead takes a compression set becoming less resilient.

4. Repeat steps 2 and 3 several times until&#;

5. Bead is compressed to about 1/16th inch, rips apart from the body, pump room is now a water park.

Don&#;t turn your pump room into a water park &#; or even worse, a sewage tank. Align those flanges before installing expansion joints.

Did you know your water pumps can generate steam? This operator didn&#;t. In this unfortunate scenario the operator closed the pump isolation valves with the pump operating, dead-heading the pump. This situation is ok for a short duration, but eventually all that mechanical energy added to the water has to go somewhere. It went into heat. The water contained in the pump and pipe up to the isolation valves had so much energy added that it flashed to steam. The expansion joint was the first component to fail, which was fortunate for the pump. The temperatures and pressures exceeded the rubber performance limits and the joint failed, nobly sacrificing itself for the greater good of the pump and piping.

The previous example showed both temperatures and pressures out of limits. If only the temperature exceeds the rubber rating, the joint will still fail but it won&#;t be quite as spectacular. This photo illustrates a hard-boiled expansion joint. Rubber turns hard and brittle when exposed to temperatures exceeding the published limits. It won&#;t be immediate, but over time the rubber will essentially transform into something resembling plastic. And it will no longer move. This is bad.

Vacuum sucks. Literally. A vacuum is any point in the pipe where the pressure drops below atmospheric pressure (14.7 psia/29.92&#; Hg). There are some expansion joints that can deal with a partial vacuum, and some that can&#;t. This unfortunate joint can&#;t. This poor spherical joint was subjected to a vacuum and over-extended itself. In building systems, expansion joints can be exposed to unintentional vacuum conditions when a riser is drained and not vented, or if a pump inlet pressure is below atmospheric pressure. Always check those operating conditions, then follow the manufacturer&#;s directions for installing your joints for the conditions!

Material compatibility issue? When your expansion joint turns to goo, that&#;s a very good first guess. This is the most unfortunate aftermath of the media reacting with the rubber. This situation could have been avoided by selecting a different elastomer.

Absent from these photos is the expansion joint&#;s trusty sidekick, the control rods. Control rods are not necessarily required for every installation, but they are always a good idea. Consider control rods as cheap insurance, preventing expansion joints from over-extending or over-compressing. A control rod assembly will avoid problems related to excessive movement.

One more item the author has encountered at EVERY site where a rubber joint failed is loose bolts. This is no exaggeration. EVERY failure site had expansion joints with bolts that could be removed without tools &#; even on joints that were not involved in the failure. Although manufacturers have different bolt tightening requirements, the one common thread (bad pun intended) is that bolts must be re-tightened after the initial installation.

What do all these failures have in common? It all boils down to human error. Each incident could have been avoided by following the manufacturer&#;s instructions and effectively communicating the application requirements prior to ordering the expansion joint. Convincing people to follow instructions can be a futile effort. Communicating application requirements, by contrast, is easy. Appendix L, p.49, of the Piping Expansion Joint Handbook has one single information sheet that can eliminate many of the problems shown in this article.

The Fluid Sealing Association&#;s Piping Expansion Joint Handbook and KnowledgeBase contain a wealth of information, so consult these resources early and often during the project.

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