There are certain conditions under which even the best-designed expansion joints will fail. It’s very important that these reasons for failure are understood, so that they can be minimized to the greatest extent possible. Since expansion joints often serve critical roles in protecting vital equipment and preventing impact or friction between two components or structures, failure could result in damage to expensive equipment, and in some cases even a complete breakdown of safety. That being so, here are some of the most common reasons why expansion joints fail during operation.
Bellows Material Failures
The bellows component of an expansion joint is the flexible element, which is intended to absorb expansion or vibration. Most bellows material failures result from stress corrosion cracking, in response to contact with chlorides, and this is especially true of nickel and stainless steel alloys, which have sulfides or sulfuric acids in their composition. Once the bellows become cracked, it’s only a matter of time before failure occurs.
Expansion Joint Fatigue
The term fatigue as it applies to expansion joints operation generally refers to excessive vibration or high cyclic application that cause more or less constant movement on the bellows. With the bellows expanding and contracting so frequently, and sometimes at high speed, it is only natural that eventually the bellows will simply wear out. Expansion joints have a predictable service lifetime at conditions normal to the environment which they are used in, but when conditions exceed normal, the service life of an expansion joint is shortened considerably.
Squirm of Rupture
When the system containing an expansion joint is over pressurized, squirm or rupture becomes a distinct possibility. Squirm refers to a condition in which the bellows ends are still on the same center line, but the bellows deflects all by itself once a critical pressure has been reached. Rupture of course, means that the expansion joint material has been breached and is certain to fail in a very short period of time.
Inadequate Testing
This is one of the most common mistakes people make before implementing their expansion joints. If the expansion joint has not been properly tested while in place, or has not been installed properly, the chances that it will fail in operation, even under minimal stress, are very good.
One reason testing is often overlooked is that the expansion joint is assumed to be in perfect working condition when it arrives. While that may have been true when it left the factory, it is very possible that damage could have occurred during shipping, and the unit is no longer 100% functional.
Even after proper installation and testing have been done, it's a good practice to periodically test the expansion joint while in place to ensure that it is still in good working order. The consequences of failure can be so significant that regular checking and testing of all expansion joints should be part of the everyday routine for a site where they are in use.
Improper Usage
Sometimes expansion joints are installed in applications that are simply outside the tolerable limits of its intended functionality. For instance, expansion joints may be installed in situations where pipe misalignment is excessive, or the expansion joint has been installed with an incorrect orientation.
It sometimes happens that expansion joints are installed with inadequate supports, i.e. the anchoring or the guides. In order for expansion joints to perform as they were designed to, they must be securely anchored in such a way that movement is allowed in the direction planned for, and which adequately contain the forces developed from the effects of interior pressure.
A fairly common reason for failure is the installation of expansion joints in situations that exceed design specifications such as excessive pressure, excessive movement or vibration, extremes of temperature, or even an unexpected vacuum.
Expansion joints are designed and engineered to tolerate specific ranges of forces that act upon them, and when the actual level of those forces exceed the design specifications, failure is all but assured. It is a simple matter to select an expansion joint for use which can tolerate the forces in effect at the usage site, but the level of those forces must be known accurately, so the correct expansion joint can be installed.
Make sure all your expansion joints are built to last by contacting the team at Badger Industries. At Badger, our team is committed to working with you each step of the way to ensure that your expansion joint manufacturing meets your every need and stands the test of time. From initial design and fabrication to field service and repairs, make sure your expansion joints are performing up to par and contact Badger Industries today.