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EXPANSION JOINT SELECTION 79 Expansion joint selection PRESSURE BALANCED LFP LFP Source: Freely adapted from EN 14917/EJMA In-line pressure balanced The above shows the use of an in-line pressure balanced expansion joint used to absorb axial movements in a long, straight pipe system. By utilising expansion joint this arrangement, the two fix points shown are relieved of pressure loading. Since the piping is relieved of compressive pressure loading, only a minimum of guiding is required, primarily to direct the thermal expansion of the piping into the expansion joints in an axial direction. LFP LFP Source: Freely adapted from EN 14917/EJMA Pressure balanced expansion joint located at a change The above typifies good practice in being secured by guides. Since the the use of a pressure balanced pressure thrust is absorbed by the expansion joint to absorb axial pipe expansion joint itself, and only the system expansion. Note that the forces required to deflect the expan- expansion joint is located at a change sion joint are imposed on the piping, in the direction of the piping, with the only a minimum of guiding is required. elbow and the end of the pipe system Directional guiding adjacent to the of direction expansion joint, as shown, may suffice in most cases. In long, small-diameter pipe systems, additional guiding may be necessary. B022016-1 – Subject to alterations and eventual misprints www.belman.com
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80 Expansion joint selection PRESSURE BALANCED Source: Freely adapted from EN 14917/EJMA In-line pressure balanced When two process vessels are to be connected, a pressure-balanced expansion joint will usually provide the best solution. This solution should include absorbing the growth of the interconnecting pipework, accepting movement due to any differential growth of the vessels and catering for the effects of any settlement. The design of process vessels will often prevent any significant loads from the pipework being applied to the vessel or nozzles. Through the utilisation of a pressure balanced expansion joint, all forces generated by internal pressure expansion joint between two acting on the expansion joint bellows are contained by the restraining structure on the unit. This leaves the spring rate forces created by the bellows movement to be contained, in most cases these forces are signifi- cantly less than those of the pressure forces and typically are easily resolved. The alternative to using a pressure balanced system would be to deploy simple unrestrained expansion joints. However, this would require the installation of a structure to enable fix points to be included. This could create significant costs, process vessels particularly when the interconnecting pipework is at greater heights. In some applications, a simple in-line axial pressure balanced unit can be used. This style of expansion joint will accept mainly axial movement, but can be designed to additionally accept small lateral movements. In more complex arrangements, special expansion joints are required with a twin-bellows incorporated to accept greater lateral movements. www.belman.com B022016-1 – Subject to alterations and eventual misprints
