When applications exist where anchoring is impractical for structural or economic reasons, such as an elevated piping application or short, straight pipe runs between two large vessels, the in-line pressure balanced expansion joint is a powerful solution to a difficult design problem. The principle of this type of unit is essentially the same as the pressure balanced elbow type, in that the pressure thrust from the two flow bellows is compensated by the pressure thrust generated by the larger balancing bellows.
The in-line pressure balanced expansion joint is designed to absorb axial movement and/or lateral deflection while restraining the pressure thrust by means of tie devices interconnecting the line bellows with outboard compensating bellows also subjected to line pressure. Each bellows set is designed to absorb the axial movement and usually the line bellows will absorb the lateral deflection. This type of expansion joint is used in a straight run of piping.
The in-line pressure balanced expansion joints are obviously more expensive than the simpler types; however, they may result in a lower overall system cost when the elimination of main anchoring is considered. This expansion joint can also be used to replace pipe loops, and it’s cost advantage may be seen in reduced pumping energy by the elimination of the loop’s elbow-generated pressure losses. This may also allow reducing the pipe size for the entire system. (View our article on the Advantages of an “Expansion Joint” versus a “Pipe Loop”)
Examples of In-line Pressure Balanced Expansion Joints:
14″ In-line Pressure Balanced Expansion Joint with PTFE Lining on all Internal Surfaces Designed for a Highly Corrosive Application
63″ In-line Pressure Balanced Expansion Joint with Refractory Lining Designed with Inconel 625 LCF Bellows for a Clean Fuels Project