Expansion joint with Tie rods

[Nukie]

I would like to know if the torque applied to the Tie Rod spherical washer nut of a joint who is installed for flanges misalignment purposes has an impact on how the joint will works ?

As I understand this, if the nut on spherical washer are loose,
the joint will have less rigidity and will be free to move much more than his design, and the rods will be bent in the worst conditions like seismic
And the joint will have

if the nut on spherical washer are too tight,
the joint will have more rigidity and will not be able to move over the elastic limit of the rods and will also cause the rod to be bent.

Does a basic reference to evaluate the required torque exist ?

Thanks

 

[KernOily]

I think I would take this up with the expansion joint manufacturer. Or, call up Flexsonics and discuss it with their people.

I do know that the joint stiffnesses are a function of the friction developed between the nut and its bearing surface, but to what degree I do not know. One standard practice is to design for the bellows stiffness and add 20% before calcuating the resulting in-service deflections and piping reactions. When the joint goes into service and pressures up, the nuts are loaded anyway, but not to the degree they'd be if pretensioned.

The manufacturer should supply installation instructions with the joints. The joints I've specified and installed all had the tie-rod nuts run up finger-tight and then tack-welded before the line went into service. Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com

 

[stanier]

Take this up with Red Valve as they are very experienced in producing rubber bellows with tie rods.

http://www.red.com

 

[ChasBean1]

These control rods (wow, sounds nuclear) are to prevent excessive expansion of the bellows joint. If it's a 9-inch joint and it is designed to have 1.25" of expansion, the locknuts on the control rods should be no more than 10.25 inches apart. They should NOT be tight under normal conditions. They should flap 'flappily' until under maximum system pressure. They are to prevent excessive extension of the joint. Just think - if they are torqued, what would be the purpose of the joint??

 

[Nukie]

ChasBean1,
keep in mind that this expansion joint has no purposes of expansion at all.
It is employed only to compensate the flange misalignement,
So there is no need for axial compression or extension in this case.

Regards

 

[ChasBean1]

Sorry Nukie, I guess we were talking apples and oranges. Did you mean the Flexicraft model? If so, try going here:

http://www.flexicraft.com/p1.asp?catid=2

If this is the one, the joint will expand under increased system pressure and the control arms are there to keep from over-expanding. If not, I apologize if I mislead. -Chas

 

[lonestar]

Well to start with there are two types of rods used in an expansion joint. One is a Tie Rod and the other is Control Rod or also called as limit rod.

1. If a Tie rod is used it essentially ties the Expansion joint and prevents it from transmitting the End Thrust to the anchor. This joint will take only Lateral movement. Hence this type of joint is called as Tied Lateral Expansion Joint. It is popular practice to use Spherical washer in this type of application. When we use a spherical washer it has some friction factor, which the joint manufacturers have to provide. To reduce the friction it is also popular to use some Teflon layer on the contact point. The tie rod has to be designed for the full pressure thrust load and also any additional load that the system gives.

2. Control rods are basically axial movement limiters. Certain amount of movement is set on the joint initially. Once the movement is reached it will not permit the system to impart any more movement thereby it will become as good as a spool. As an expansion joint is the weakest element in the piping system there is a possibility that it fails due to excessive movement caused due to extraneous reasons such as anchor failure of wrong calculation. Control rods prevent this failure. Its not normal practice to provide spherical washers for this but control rods are also designed for full pressure thrust load similar to Tie Rods.

You may contact

http://www.igp-group.com

for more information on this.