Piping stress analysis can use code ASME B31.1 as reference calculation and design. Code ASME B31.1 for power piping analysis is belonging to the American society of mechanical engineers. In code ASME B31.1 there are empirical formulas that apply to the sustain load, expansion load, and the combination of sustain and expansion load (during operations), and also occasional load are described as the following below:
The stresses (S) that occur due to sustain the load such as pressure, weight and other mechanical loads can be expressed by the equation as follows:
(P Do / 4 tn) + 1000(0.75 i Ma / Z) ≤ 1.0 Sh
- Range Thermal Expansion Load
The stresses that occur due to thermal expansion can be expressed as the equation below:
SE = 1000(i Mc / Z) ≤ SA + f(Sh – SL)
- Combination Load of Sustain load and Thermal Expansion Load
The stresses due to combination of sustained load and thermal expansion load (Sls + SE), can be calculated with the equation:
Sls + SE = (P Do / 4 tn) + 1000(0.75 i Ma / Z) + 1000(i Mc / Z) ≤ (Sh + Sa)
The stresses that occur due to pressure, weight, and other sustain load can be expressed as the equation below:
(P Do / 4 tn) + 1000(0.75 i Ma / Z) + 1000(i Mc / Z) ≤ K Sh
Where:
P = internal design pressure (psi)
Do = outside diameter (in)
Ma = Moment due to sustain load (in-lbs)
Mb = Moment due to occasional load (in-lbs)
Mc = Range of the moment due to thermal expansion (in-lbs)
Z = section modulus of the pipe (in3)
tn = nominal wall thickness of pipe (in)
i = stress intensification factor
K equal to 1.15 for the occasional load which work less than 1% of the operating period and is equal to 1.20 for the occasional load which work less than 10% of the operating period.