5.0 Pressure & Bending Stress & Combination Application:
The code confines the stress examination to the most significant stresses created by the diversity of loading to which a piping system is subjected. They are:
i)Stress due to the thermal expansion of the line.
ii)The longitudinal stresses due to internal or external pressure.
iii)The bending stress created by the weight of the pipe and its insulation* the internal fluid* fittings* valves and external loading such as wind* earthquake etc.
5.1 Stresses due to the thermal expansion of the line:
Temperature change in restrained piping cause bending stresses in single plane systems* and bending and torsional stresses in three-dimensional system. The maximum stress due to thermal* changes solely is called expansion stress SE. This stress must be within the allowable stress range SA.
SE = Sb2 + 4St2
Sb = I (Mb / Z) = resulting bending stress
Mt = (Mt //2Z) = torsional stress
Mb = resulting bending movement
Mt / = torsional movement
Z = section modules of pipe
i = stress intensification factor
5.2 Longitudinal stress due to internal or external pressure:
The longitudinal stress due to internal/external pressure shall be expressed as P (Ai / Am)
Where Ai is inside cross sectional area of pipe* Am is the metal area* P is the pressure.
5.3 Weight Stress:
The stress induced* self weight of pipe* fluid* fittings etc. as given by SW = M/Z* Where M is bending moment created by the pipe and other fittings* Z is the section modules of the pipe.
The stresses due to internal pressure and weight of the piping are permanently sustained. They do not participate in stress reductions due to relaxation and are excluded from the comparison of which as the latter has been adjusted to allow for them with the following provision.