Rubber Bellows vs Metal Bellows Expansion Joints 4

First of all, you need to be aware that a tank has some different characteristics then we normally see in a vessel. The nozzle at the bottom of tank will rotate downwards. This is due the shell deflecting out when the tank is full. For this reason it is not a good idea to anchor such a nozzle per pennpipers comments.

If can can avoid using an expansion joint, then great. If you have tried all other options then here is your approach: Your expansion joint selection should be done in conjunction with your pipe support design to resolve the forces on both your pump and tank nozzle. These go hand in hand. You will want to obtain the properties (axial, lateral, rotation and torsional stiffness's) of the joint you intent on using, or close too. This will allow you to determine the actual loads you will see on the pump nozzle. Your supports will protect the expansion joint from undesired deflections. Locating near the pump suction nozzle makes it easier the resolve nozzle loading as you are not dealing with friction from supports prior to the nozzle (if the joint was located somewhere else).

Your pressure is low so you won't have too much of an issue with pressure thrust but you must understand it, both now and moving forward.

I would not recommend using an expansion joint simply because of vibration unless it is the result of some previous concern or modal analysis. The pump should be on a solid foundation, base plate/frame and well balanced. The piping should be properly aligned prior to final bolt up, etc.

Expansion loops are rarely desirable in a pump suction lines. You have some straight lengths as you have mentioned. Carefully go through your design, minimize where you can see if you can solve this with one expansion joint. If your flow rates are low enough remember an 18" expansion joint will be cheaper that a 30" one. As I mentioned, make the supports work with your expansion joint to solve the problem after you have exhausted all other possibilities.

Conor Walshe



Bellows Manufacturing and Research, Inc.

Edward hit on a lot of good points and I'd like to add to them.First of all, you need to be aware that a tank has some different characteristics then we normally see in a vessel. The nozzle at the bottom of tank will rotate downwards. This is due the shell deflecting out when the tank is full. For this reason it is not a good idea to anchor such a nozzle per pennpipers comments.If can can avoid using an expansion joint, then great. If you have tried all other options then here is your approach: Your expansion joint selection should be done in conjunction with your pipe support design to resolve the forces on both your pump and tank nozzle. These go hand in hand. You will want to obtain the properties (axial, lateral, rotation and torsional stiffness's) of the joint you intent on using, or close too. This will allow you to determine the actual loads you will see on the pump nozzle. Your supports will protect the expansion joint from undesired deflections. Locating near the pump suction nozzle makes it easier the resolve nozzle loading as you are not dealing with friction from supports prior to the nozzle (if the joint was located somewhere else).Your pressure is low so you won't have too much of an issue with pressure thrust but you must understand it, both now and moving forward.I would not recommend using an expansion joint simply because of vibration unless it is the result of some previous concern or modal analysis. The pump should be on a solid foundation, base plate/frame and well balanced. The piping should be properly aligned prior to final bolt up, etc.Expansion loops are rarely desirable in a pump suction lines. You have some straight lengths as you have mentioned. Carefully go through your design, minimize where you can see if you can solve this with one expansion joint. If your flow rates are low enough remember an 18" expansion joint will be cheaper that a 30" one. As I mentioned, make the supports work with your expansion joint to solve the problem after you have exhausted all other possibilities.Conor WalsheBellows Manufacturing and Research, Inc.

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