|Figure 1: Cylindrical Part Under Pressure|
Steam boiler consist a lot of cylindrical parts such as tube, pipe, header and drum. All cylindrical parts are performed under stress. Designer steam boiler shall have good knowledge to design and calculate stress on these parts. Based on location, stress can be classified by two types; internal stress and external stress. Internal stress is stress which is occurring inside cylindrical part while external stress occurs because of load from outside cylindrical parts.
Tube, pipe, header and drum must be designed and calculate internal pressure first to prevent deformation on that parts. Internal stress consists of two types, longitudinal stress and circumferential stress. Longitudinal stress is caused by lengthwise of axial load and circumferential stress can be called as hoop stress is caused pressure which working cylindrically. For illustration please see figure 1.
The formula of longitudinal stress can be expressed as: SL = P D / 2 t
The formula of circumferential stress can be expressed as: SC = P D / 4 t
SL = Longitudinal Stress (psi)
SC = Circumferential Stress (psi)
D = Outside Diameter Cylindrical Part (in)
P = Internal Pressure (psi)
T = Thickness of Cylindrical Part (in)