SECRETS OF SELECTING THE RIGHT METAL BELLOWS EXPANSION JOINT
- Choose an expansion joint manufacturer that you trust and one that has your best interest in mind. Working with an experienced expansion joint designer can take the guesswork out of the selection process. Deciding on the right bellows materials or expansion joint configuration can be overwhelming.
- As a design engineer it has always been my goal to provide our customers with the best suited, longest lasting expansion joint products at the lowest price. To achieve my goal however requires that I get all of the necessary information from the customer. It can get frustrating when people don’t take the time to get all of the facts. Expansion joints are rarely an off the shelf, one size fits all products. Designing to suit each individual application produces the best results and doesn’t cost any more to build. In fact often times when customers do not do their due diligence the expansion joints and metal bellows end up costing much more than they should.
- NEVER GUESS! If you do not know the pressure and temperature, find out! Somebody has that important piece of information. Don’t assume that just because the expansion joint that you are replacing has class 150# flanges you should order an expansion joint rated for 150 psig. This assumption may get you in trouble or cost you more money than necessary for a product that will not last as long as it might have. Did you know that a class 150# forged steel flange is actually rated for a maximum working pressure of 285 psig @100ºf? If your expansion joint manufacturer only designs the bellows for 150 psig a failure will occur at the potential higher pressures if you guess wrong. OOPS! If the system pressure is low and you design for high pressure the expansion joint will unnecessarily cost you more and what is worse it will not last as long, needing to be replaced sooner. A good rule of thumb to remember is the higher the pressure the thicker the bellows material. The thicker the bellows material the greater the material and labor costs are. The thicker the material the lower the theoretical cycle life will be.
- Tell your metal expansion joint supplier that you want multi-ply bellows construction. Expansion joints fabricated with metal bellows constructed with multiple, thinner layers of material, will last significantly longer than a single ply bellows made with thicker sheet metal. Best of all multi-ply bellows do not cost that much more than single ply bellows. Since the bellows element is the weak link in the piping system why not design for the ultimate performance with the proven multi-ply design?
- For peace of mind ask your bellows expansion joint supplier to furnish you with a bellows design data sheet. The metal bellows used in your expansion joint should be designed and manufactured in accordance with EJMA, the Expansion Joint Manufacturers Association. While some of the information on the printout may not interest you here are some things to look for. Verify that the bellows is designed for the correct pressure and temperature. Verify that the axial and lateral movements are correct. The fatigue cycles are important to calculate how long your expansion joints will theoretically last. Say for example the data sheet for a single ply bellows calculated 300 cycles. If your expansion joint cycled once per day it would fail in less than a year. If you are not satisfied with cycle life or spring rates that your expansion joint supplier is offering let them know you want better. Some unscrupulous expansion joint manufacturers would like to sell you a new expansion joint every year but as an informed consumer you can do much better than that. The best advice that I gave you is to work with a metal bellows expansion joint manufacturer that you trust.