How to Troubleshoot Expansion Joint Failures

Written by Fluid Sealing Association

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Rubber Deterioration

If the joint feels soft or gummy, plan to replace the expansion joint as soon as possible. Chemical attack is the most likely cause. Joints can be made compatible with almost any media, so it is vital that the manufacturer be advised as to what media will contact the joint when reordering.

Leakage (see the image below)

It is most important to determine where the leak originated prior to implementing any corrective action. 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. (Make sure that a gasket has NOT been installed between the joint's flange face and the mating flange.)

If this is not successful, turn off the system pressure, loosen all flange bolts and then retighten bolts in stages by alternating around the flange. Make sure there are washers under the bolt heads, particularly at the split in the retaining rings. There should be no gap at the retaining ring split. Remove the expansion joint and inspect both rubber flanges and pipe mating flange faces for damage and surface condition. Repair or replace as required. Also, make sure the expansion joint is not over-elongated as this can tend to pull the joint flange away from the mating flange resulting in leakage. If leakage persists, consult the manufacturer for additional recommendations.

Root Causes Include: Under-torqued bolts; irregular sealing surface (optimal mating surface is full face flat flanges); over-extension; and chemical attack by the media.

Corrective Action: Tighten the bolts to the manufacturer's torque recommendations. Change to proper design and chemically compatible material. Measure the face-to-face dimension prior to replacement.

Replacement Criteria

If an expansion joint is in a critical service and is five or more years old, consideration should be given to maintaining a spare or replacing the unit at a scheduled outage. If the service is not critical in nature, observe the expansion joint on a regular basis and plan to replace after ten years service to ensure a margin of safety. Applications vary and life can be as long as 30 years in some cases.

Summary

Rubber expansion joints have been specified and successfully used for many years to accommodate pressure loads, relieve movement stresses, reduce noise, isolate vibration, compensate for misalignment after plants go on stream and prolong the life of pumps and other motive equipment. Periodic inspection to confirm satisfactory installation and operation is important to ensure reliability. Plant-approved maintenance procedures should be applied as required.

Once in service, the expansion joint should be protected from any ozone generating processes such as nearby welding. Proper storage in a cool dry location prior to installation will help prolong service life. It is always prudent to consult the manufacturers for questions dealing with any aspect of expansion joint application.

Next Month: What is the most effective seal design when misalignment is present?

We invite your questions on sealing issues and will provide best efforts answers based on FSA publications.

Fluid Sealing Association

Sealing Sense is produced by the Fluid Sealing Association as part of our commitment to industry consensus technical education for pump users, contractors, distributors, OEMs, and reps. This month's Sealing Sense was prepared by FSA Member Lloyd Aanonsen. As a source of technical information on sealing systems and devices, and in cooperation with the European Sealing Association, the FSA also supports development of harmonized standards in all areas of fluid sealing technology. The education is provided in the public interest to enable a balanced assessment of the most effective solutions to pump systems technology issues on rational Total Life Cycle Cost principles.

The Piping Systems Non-Metallic Expansion Joint division of the FSA is one of five with a specific product technology focus. As part of their mission they develop publications such as the Technical Handbook Non-Metallic Expansion Joints and Flexible Pipe Connectors and the Non-Metallic Piping Expansion Joint Installation Guide. The former provides construction, installation, and application details while the latter is a "hands-on" simplified guide for maintenance operators and engineers. Both are primers intended to complement manufacturer's documents produced by the member companies. In addition, standards such as FSA-PSJ-701-06 Non-Metallic Expansion Joint Hydrotesting and Vacuum Testing, FSA-PSJ-702-06 Rubber Flanged Non-Metallic Expansion Joint Installation, Maintenance, and Storage, and FSA-NMEJ-703-99 Specifications of Elastomers Used in Piping Systems Non-Metallic Expansion Joints have been developed in response to important user issues.

The following members of the Piping Systems Non-Metallic Expansion Joint division sponsor this Sealing Sense: