integrated silencer bellows seals (sbs) -...

1 Expansion Joint Systems, Inc.

10035 Prospect Avenue, Suite 202, Santee, CA 92071 (619) 562-6083 Fax (619) 562-0636 E-mail:[email protected] Website: www.ejsus.com

PS# 12rev 3 01.09

Integrated Silencer Bellows Seals (SBS)

Silencer Bellows Seal attached Externally

on the Silencer

In the past, bellows seals for Silencers have been known to be very complex and expensive. By integrating a low-pressure expansion joint with the silencer, EJS has developed a more cost effective solution to accommodate the large thermal growth problems of the connecting piping from safety relief and vent valves. Safety and vent relief piping typically handles high-pressure steam from a boiler when the valves are opened to reduce pressure or control various processes. This causes the interconnecting pipes to thermally move in order to accommodate the temperature change. Along with this movement, the boiler's thermal growth must be absorbed, as the fixed point of the silencer is normally independent of the boiler. In the past, expansion joints were used to interconnect the piping. This method was considered to be more complex and expensive due to the high pressures produced by the instantaneous release of steam when the valves were opened and the large movements caused by the high temperature. By combining an SBS unit into the silencer itself, a simple, yet effective method of absorbing the movement while exposing the bellows to the low pressure inside the silencer is achieved.

All the thermal movements caused by daily boiler activity and valve opening is absorbed by the seal easily and economically. For seals fitted externally on the silencer, EJS can provide sound attenuation covers if required. As the use of these seals has expanded, the seal is now typically fitted inside the silencer, eliminating the need for sound covers and providing more protection to the seal. Silencer Bellows Seals (SBS) are integrated directly into the silencer exposing the seal to the low-pressure side of the system after the steam has entered the silencer and has been diffused. Although the line and inlet pressure may exceed 1000 psig, the bellows seal is only exposed to the pressure within the silencer, which is typically below 25 psig. The standard seals are designed to take +/- 1" of axial movement and 2" of lateral movement; however, larger movements are easily accommodated and can be specified to the silencer manufacturer. A silencer manufacturer will typically integrate the SBS units into the their silencer, as the inlet diffuser has to be modified to accept the seal. EJS can refer you to a silencer manufacturer who has realized tremendous cost savings for their customers by using the SBS units in their silencers.

Silencer Bellows Seal integrated inside the silencer offering a

convenient and economical solution for the end user

Steam Relief Valve Expansion Joints (SRV)

Expansion Joint Systems, Inc. (800) 482-2808 (619) 562-6083 Fax: (619) 562-0636 E: [email protected] W: www.ejsus.com

With every high-pressure steam system the effects of pressure thrust have to be taken into consideration. Introduce an expansion joint and it becomes critical that the system is properly restrained. Steam Relief Valve (SRV) expansion joints are designed for installation on pressure vessel safety relief valve lines to absorb thermal movement and to restrain against pressure thrust forces preventing damage to structures and the valves themselves.

The thermal movements seen on a Steam Relief Valve system are:

• Normal everyday movement of the SRV itself as a result of normal adjacent system temperature

• Additional thermal movement when the SRV opens; due to the rapid steam flow through the pipe

Most expansion joints used in SRV lines are restrained type (tied universals) joints; therefore the positioning of the joint is important. When using a tied expansion joint, all axial movement must be confined within the tie rods. The remaining movements are taken laterally. If axial movement has to be absorbed from outside the tie rods then a balanced joint is a better solution. Another option, which is occasionally used, is a 3-hinge system. An EJS representative can fully address each option and the optimal installation scenario on a case-by-case basis.

P

Atmosphere

P

∝

∝

∝

∝

∝X ∝Y

∝

⊕

P

P1 = valve set pressure P2 = 10% P3 = 50% P2 Pdesign = 2 x P2 for piping components

When calculating the design pressure for theSafety Relief Valve (SRV) Expansion Joint, take10% of the SRV set pressure and multiply it by asafety factor of 2. The orifice diameter of theSRV is smaller than the diameter of the reliefpiping, therefore, the design pressure of theexpansion joint is much lower than the setpressure of the SRV.

Example: P1 = set pressure of the SRV P2 = line pressure Pdesign = 2:1 safety

P1 = 685 PSI P2 = 68.5 PSI Pdesign = 137 PSI (150 PSI)

All the piping components of the SRV line

should be designed to the above to meet ANSI.However, the reality is much different. If theexhaust silencer backpressure is designed for 15PSIG., then the true pressure that the expansionjoint will be exposed to is relative to its positionin the piping system.

Note: Piping flexibility is very important on this type of system. Neither the SRV nor the silencer is able to withstand high loads imposed by thermal growth. Before using an expansion joint, analyze the piping carefully. You may find that it is flexible enough not to require expansion joints. Introducing an expansion joint in any piping or ducting system may also introduce Pressure Thrust; that is unless the joint is a restrained or a balanced type. Most expansion joints used in SRV lines are restrained type (tied universals) joints, therefore the positioning of the joint is important. When using a tied expansion joint, all axial movement has to be confined within the tie rods. The remaining movements are taken laterally.



If axial movement has to be absorbed from outside the tie rods then a balanced joint may have to be used. 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 two conditions are usually denoted by lower case xyz for the SRV and upper case XYZ for the pipe.

∝x = +0.5” ∝X = -0.3” ∑∝xX = 0.8” ∝y = +0.75” ∝Y = 0.0” ∑∝yY = 0.75” ∝z = +0.018” ∝Z = +0.92” ∑∝zZ = 0.92” ∝z can be taken by the piping.

If the joint is not tied or balanced Pressure Thrust will be imposed as shown. (Area of bellows x pressure = PT)

On low pressure lines, the pressure thrust is not high enough to warrant tie rods. For example, on a 12” line at 200 PSIG the pressure thrust is 3958 lbs.f. A straight pipe run between the silencer and the SRV is the most difficult arrangement to solve inexpensively. A one-plane system, as shown, is the optimum arrangement. Even if another horizontal run is added to the “Y” plane it will only introduce another lateral movement. The joint could not be put into the vertical position because the movement of the SRV in “x” could not be accommodated without the use of a balanced expansion joint which is more expensive. Other solutions are possible like a 3-pin hinge system, however the tied universal is probably the most cost effective in this arrangement.

PT PT



Oversize bellows; smooth flow SRV liners

Pressure-balanced SRV joint.Typical 3-hinge system; pre-fabricated by EJS

Another factor to consider affecting SRV expansion joints is the flow rate. The flow rate is often near supersonic and normal welded liners will not withstand such high velocities. Instead, EJS provides all SRV expansion joints with “oversize bellows.” These enable through bore liners to be used. As you can see in most of these photographs there are reducers on either side of the bellows. The pipe continues through the joint giving unobstructed flow. You may also use this feature to change the pipe size at the expansion joint; the downstream end of the joint is one pipe size larger than the upstream end. Please feel free to send EJS a simple piping layout. We would be pleased to advise you of where the expansion joints and supports should be located. EJS will always find the most cost-effective solution without compromising safety or efficiency.

integrated silencer bellows seals (sbs) -...

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