BS 7159 - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II Version
12

BS 7159 for Fiberglass Reinforced Plastic (FRP) pipe requires that you evaluate the operating load case only. You must verify the following operating load case combined stress requirements are met:

If Sx is tensile:

(OPE)

and

(OPE)

or

if Sx is compressive:

If Fx/A > P(Dm)/(4t) and it is compressive

(OPE)

and

(OPE)

Circumferential Stress

for straight pipes

for bends

for tees

Dm and t are always for the Run Pipe

Calculate the allowable stress limits using BS 7159

BS 7159 allowables are based on material design strain ed. Alowable stresses differ in the axial and hoop directions by the ratio of the axial and hoop moduli of elasticity:

Sh = edEx SHOOP = (edEx) (Eh/Ex)

Enter the ratio Eh/Ex in the allowable stress Eff field. If left blank, the value defaults to 1.0 for isotropic materials.

Calculate pressure stiffening using BS 7159

Pressure stiffening of bends is done assuming the bends are fully pressurized up to the design strain of the components. You can exclude pressure stiffening on bends by including the Use Pressure Stiffening option in the configuration file.

BS 7159 does not by default add F/A into the stress calculation (unless this puts an element into compression as described above). Use the Add F/A in Stress option to tell CAESAR II to include the axial force term into the code stress.

Calculate the fatigue factor using BS 7159

The fatigue factor Kn is used inversely relative to the cyclic reduction factor in most codes, so its value should be greater than or equal to 1.0 (allowable stress is divided by this number). Kn is calculated as:

Kn = 1.0 + 0.25 (As/sn) (Log10(n) - 3.0)

Where:

As = Stress Range During Fatigue Cycle

sn = Maximum Stress During Fatigue Cycle

n = Number of Cycles During Design Life

Enter Kn in the Cyclic Reduction Factor fields.

BS 7159 requires that you consider the thermal strain of the pipe material as being from 80% - 85% below the true material strain due to insulation effects of the pipe wall. Enter this reduction factor K in the allowable stress FAC field. If left blank, this value defaults to 1.0.

Calculate the stress intensity and flexibility factors of bends using BS 7159

The stress intensity and flexibility factors of bends vary based on laminate type:

  • All chopped strand mat (CSM) construction with internal and external surface tissue reinforced layer.

  • CSM and woven roving (WR) construction with internal and external surface tissue reinforced layer.

  • CSM and multi-filament roving construction with internal and external surface tissue reinforced layer.

You can enter the laminate type in the Bend Type field, or set the type default on the Special Execution Parameter dialog box.

Calculate SIFs for Reducers using BS 7159

BS 7159 does not mention reducers for SIF calculations.