WEAR™ Restraints
WEAR™ Restraint Structural Considerations
Enidine Pipe Restraint Application Information
WEAR™ (Wire Energy Absorbing Rope) restraints are a single axis
combined spring-dashpot device. In applications that incorporate
WEAR™ restraints into a piping design to control steady state
vibration, damping is added to the system by small displacements
imparted into the WEAR™ unit. As a result, the structure that the
WEAR™ restraint is connected to must have adequate stiffness in
the direction of the restraint axis so the WEAR™ restraint deflects
vs. the structure. The WEAR™ restraint and connecting structure
act as two springs in series. If the structure is soft relative to
the restraint, then the pipe steady state vibration pipe displacement
will be imparted to the structure rather than the WEAR™ restraint.
This results in two issues: first the structure is excited which is
undesirable and second, the WEAR™ restraint imparts no damping
to the piping system.
Good design practice is to connect the WEAR™restraint to a
structure, including any support auxiliary steel, with a stiffness
that is an order of magnitude greater than the WEAR™ stiffness.
To quantify this, the structural stiffness should be 10 times the
WEAR™ tangential stiffness in the hot restraint position.
Since the WEAR™ restraint is a non-linear device, the
tangential stiffness varies with the position of the restraint.
The WEAR™ restraint is typically modeled as a Bi-Linear spring and
Mid-stroke and Max-Stroke stiffness values are provided in the
WEAR™ catalog. In most vibration applications, it is recommended
that the hot restraint setting be equal to 50% of the restraints total
half travel so as to maximize the amount of damping added to the
system. Thus, for a restraint with a total travel of +1.5 inches, the
recommended hot position would be either +0.75 inch or -0.75 inch
depending on the growth direction of the pipe. A conservative estimate
of the tangential stiffness at this setting is the published Max-Stroke
Stiffness value for the particular restraint.
Thus, the recommended structural stiffness should be 10 times the Max-Stroke stiffness value provided in the WEAR™
catalog. Since this stiffness is an upper bound approximation of the tangential stiffness of the restraint in the hot position,
a lower structural stiffness may be acceptable. As a minimum value, at least 5 times the Max-Stroke stiffness should be available
for the structure including any restraint auxiliary steel utilized in the design. As an example, the recommended structural
stiffness for a WEAR™ 24 kip with a +1.5 inch stoke would be 10 times 16,000 lb/in or 160,000 lb/inch with a minimum
value of 5 times 160,000 or 80,000 lb/in.

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