DESIGN METHOD:
LONGITUDINAL STRESS VS. TEMPERATURE CHANGE⬇️
Longitudinal Stress = σT = α (T2-T1) Es
And
Longitudinal Force = Ft = (σT) A
Where:
σt = Theoretical longitudinal stress, psi
Where: positive values = expansion
negative values = contraction
α = coefficient of expansion or contraction (as in Equation 1)
α = 1.0 to 1.1 x 10-4 in/in/°F for PE 3408 materials
α = 1.0 x 10-4 in/in/°F for PE 2406 materials
T1 = initial temperature oF
T2 = final temperature oF
ES = apparent short term modulus of elasticity, psi
(see Table 1) at lowest temperature
Ft = Theoretical longitudinal force, lbs
A = pipe wall cross sectional area, in2
LONGITUDINAL STRESS VS. TEMPERATURE CHANGE⬇️
Longitudinal Stress = σT = α (T2-T1) Es
And
Longitudinal Force = Ft = (σT) A
Where:
σt = Theoretical longitudinal stress, psi
Where: positive values = expansion
negative values = contraction
α = coefficient of expansion or contraction (as in Equation 1)
α = 1.0 to 1.1 x 10-4 in/in/°F for PE 3408 materials
α = 1.0 x 10-4 in/in/°F for PE 2406 materials
T1 = initial temperature oF
T2 = final temperature oF
ES = apparent short term modulus of elasticity, psi
(see Table 1) at lowest temperature
Ft = Theoretical longitudinal force, lbs
A = pipe wall cross sectional area, in2
Anchor and Support Design⬇️
Proper design of anchors and supports is as important with PE piping as it is with other piping materials. A variety of factors must be considered.
Proper design of anchors and supports is as important with PE piping as it is with other piping materials. A variety of factors must be considered.
1-Some installations of PE pipe have the pipe lying directly on the earth’s surface. In
this type of installation, the surface under the pipe must be free from boulders,
crevices or other irregularities that could create a point-loading stress situation on the
pipe.
this type of installation, the surface under the pipe must be free from boulders,
crevices or other irregularities that could create a point-loading stress situation on the
pipe.
2-On grade placement over bed rock or hard pan should be avoided unless a uniform
bed of material is prepared that will cushion the pipe. If the PE pipe rests directly on
a hard surface, this creates a point loading situation and can increase abrasion of the
outer pipe surface as it “wanders” in response to temperature variations.
bed of material is prepared that will cushion the pipe. If the PE pipe rests directly on
a hard surface, this creates a point loading situation and can increase abrasion of the
outer pipe surface as it “wanders” in response to temperature variations.
3-Intermittent pipe supports should be spaced properly using the design parameters
discussed in the preceding pages. Anywhere unusual loadings or excessive
temperatures are encountered, continuous support should be considered.
discussed in the preceding pages. Anywhere unusual loadings or excessive
temperatures are encountered, continuous support should be considered.
4-Supports that simply cradle the pipe, rather than grip or clamp the pipe, should be
from one half to one pipe diameter in length and should support at least 120 degrees
or one third of the pipe perimeter. All supports should be free from sharp edges.
from one half to one pipe diameter in length and should support at least 120 degrees
or one third of the pipe perimeter. All supports should be free from sharp edges.
5-The supports should have adequate strength to restrain the pipe from lateral or
longitudinal deflection given the anticipated service conditions. If the design allows
free movement during expansion, the sliding supports should provide a guide without
restraint in the direction of movement. If, on the other hand, the support is designed
to grip the pipe firmly, the support must either be mounted flexibly or have adequate
strength to withstand the anticipated stresses.
longitudinal deflection given the anticipated service conditions. If the design allows
free movement during expansion, the sliding supports should provide a guide without
restraint in the direction of movement. If, on the other hand, the support is designed
to grip the pipe firmly, the support must either be mounted flexibly or have adequate
strength to withstand the anticipated stresses.
6-Heavy fittings or flanges should be fully supported and restrained for a minimum
distance of one full pipe diameter on both sides of the PE pipe. This supported fitting
represents a rigid structure within the flexible pipe system and should be fully
isolated from bending stresses associated with beam sag or thermal deflection.
distance of one full pipe diameter on both sides of the PE pipe. This supported fitting
represents a rigid structure within the flexible pipe system and should be fully
isolated from bending stresses associated with beam sag or thermal deflection.
Flange analysis is done based on the Kellogg equivalent pressure method. In addition to internal and external pressure, axial force and bending moment can act on flanges as equivalent pressure. The values of axial force and bending moment are determined from analysis without pressure thrust effect.
These internal forces are used to determine the equivalent design pressure of flange pair by formula
Now enter PN into the ASME B 16.5 pressure-temperature rating table associated with flange material. If PN is less than the allowed pressure on the rating table corresponding to the associated temperature then flange will not leak. If flange leak, then reduce bending moment and axial force acting on the flange or select the greater class flange.