Source: Expansion Joint Systems, Inc.
Introducing an expansion joint in any piping or ducting systems may also introduce Pressure Thrust unless the joint is a restrained or balanced type
Introducing an expansion joint in any piping or ducting systems may also introduce Pressure Thrust unless the joint is a restrained or balanced type. Most expansion joints used in Steam Relief Valve (SRV) lines are restrained type (tied universals), therefore the positioning of the joint is important. To use a tied joint, all the axial movement has to be within the tie rods, the remaining movements are taken laterally.
Piping flexibility is very important on this type of system. Before using an expansion joint, analyze the piping. It may be flexible enough not to require expansion joints.
If axial movement has to be absorbed from outside the tie rods, a balanced joint is recommended. The remaining option, which is occasionally used, is a 3-hinge system. The thermal movements seen on a SRV system are two fold:
- Normal everyday movement of the SRV itself.
- Additional thermal movement when the SRV opens due to the steam flow through the pipe.
The other factor affecting SRV expansion joints is the flow rate. The flow rate is often near supersonic. Normal welded liners will not withstand such high velocities. We use "oversized bellows" in conjunction with through bore liners to allow the process pipe to continue through the joint without obstructing the flow. This will enable you to change the pipe size at the expansion joint. EJS can advise you of expansion joint and support placement within your system. EJS will always find the most cost-effective solution without compromising safety or efficiency.
Expansion Joint Systems, Inc., 10025 Prospect Avenue, Suite 202, Santee, CA 92071. Tel: 619-562-7458; Fax: 619-562-0636.