Depending on the application and service environment, metal bellows expansion joints can generally provide over 10 years of reliable service before needing replacement. Unfortunately, the bellows typically do not give any early warning signs before failure or developing leaks, and they can be difficult to weld repair.
There are various types of expansion joints: single, flanged, tied universals, hinged, gimbaled, externally pressurized, pressure-balanced and toroid expansion joints are some of the most common designs. ASME code expansion joints, penetration seals, refractory lined, multi-ply and testable bellows designs are also common types of expansion joints.
A bellows can be single-ply, multi-ply, redundant ply and reinforced. A testable bellows has two plies, each designed to accommodate the operating conditions independent of each other. If one ply fails, then the other provides the pressure containment. Bellows are subject to high bending stresses well into the plastic range to achieve the movements required by the thermal expansion of the system. The finished bellows should be uniform in shape and pitch with no forming scratches or heavy tooling marks.
Various performance analysis calculations are used to determine the theoretical life expectancy for a given design. Still, it is very difficult to determine the remaining life expectancy of a metal bellows. Without destructive testing of the bellows, we cannot see the grain condition, amount of work hardening or the creep deterioration. Visual inspection of the bellows can give good insight into the condition of the bellows. After that, there really is no other test. Specialized ultrasonic equipment can verify the bellows material thickness to ensure there has been no reduction due to erosion or corrosion.
Here are some things to look for when inspecting your installed unit.
Before a turnaround:
- Check for leaks
- If any, check multiple-ply bellows indicators (gauge or pop-up)
- Take temperature readings along the length of the joint at 3, 6, 9 and 12 o'clock positions.
Note: Pay close attention to areas closest to the bellows attachment where insulation may have been lost.
- Measure all external hardware to be compared with cold measurements (this enables operational movements to be calculated)
- Check clearances and ease of operation in all external hardware. Any binding may suggest excessive movements or bending.
- In the associated piping system, check associated guides, anchors and hangers for possible excessive movements or improper support settings.
- Discuss your findings with an expansion joint professional to assist with interpretation of observed/collected data.
- Do not remove any covers or insulation from the bellows area during operation. Close inspection of the bellows membrane MUST NOT be done when the unit is operating.
During a turnaround:
- Remove insulation and covers to inspect the bellows for damage.
- Dye penetrate test all bellows welds and outside surface as well as pipe spools for leakage and cracks.
- Check all associated hardware and anchor plates, gussets, rods and pins for damage and corrosion.
- Measure all external hardware to compare with hot measurements and thereby calculate joint movements. EagleBurgmann can assist with the calculation phase. If insulation and/or refractory loss are suspected, an internal inspection should be conducted.
- Discuss your findings with an expansion joint professional to ensure accurate identification of problems, risks and options.
The expansion joint in many environments, although designed with safety factors, is a critical link in the system. All inspection personnel should take the utmost care to protect themselves while performing inspections in the vicinity of an operating expansion joint. Most importantly, do not attempt to touch the bellows membrane while the unit is operating.
Proper installation of your expansion joints is key to increasing the service life and maintaining long-term reliability. Whether an outage or turnaround is planned or forced, choosing an expansion joint professional can help reduce costs, decrease down time and eliminate installation problems, quickly and safely. Installation specialists should have extensive experience and application knowledge to help your turnaround team with trouble shooting and onsite repairs if necessary.
In the case of an unexpected failure, a clamshell bellows is a popular option. A two-piece bellows may be welded around the failed bellows while in service. This provides undisrupted service to the end user. The intent is to leave the clamshell in place until the next turnaround when it will be inspected and evaluated for modification if required. The clamshell solution enables repairs to expansion joints without taking your plant offline and avoiding an unscheduled outage that could cost your company millions of dollars.
About EagleBurgmann Expansion Joint Solutions
EagleBurgmann EJS is one of the leading suppliers of expansion joint technology in the world. For almost 50 years, Eagle-Burgmann Expansion Joint Solutions has specialized in fabric and metal expansion joints as well as piping solutions. From piping analysis to complete installation services, EagleBurgmann EJS can support your next project or maintenance turnaround.
For more information on EagleBurgmann EJS or their products, please contact us at email@example.com.