Bends and Elbows

Bends (welded or made with pipe bending) allows a change in the piping axis direction. START-PROF takes into account the increased flexibility of bends and runs a stress analysis. Adjoining straight pipes prevent ovalization of the bend cross-section, increasing the bend's bending stiffness. There are several bend types:

Features of ASME code:

Bend Modeling

If there is no bend in a node, the connection between pipes is represented as an intersection of two pipes, rigidly connected each to other (without taking into account the bend flexibility), and stresses in adjoining elements are calculating without taking into account the stress intensification factors (fig. 1).

Fig. 1. Connection without a bend

If the bend is inserted into the node A, then nodes B and C are automatically added at the intersection of bend radius and adjoining pipes (fig. 1, a). Bends are modeled as curved rods (fig. 2, a), taking into account the Karman's effect - increased flexibility due to cross-section ovalization during bending (fig. 2, b) based on standards selected in Project Settings. Stress analysis is performed using thin casing analysis theories and according to standards selected in Project Settings. Bend weight is modeled as uniform load along the arc length. The weight of straight pipe parts that covered by bend is removed. The insulation weight, fluid weight, snow, ice, wind, and user defined uniform loads are got as average value from two connected pipes and modeled as uniform load along the curved rod. Angle used for calculation of wind load are taken as angle between wind direction and bend chord (B-C).

Bends cannot have a central angle of more than 180°

Fig. 2. Modeling bends

Bend Stress Analysis

Equivalent stress is calculated for 3 or more cross sections: a, b, c, ... (fig. 3). The largest of the two values is taken. For long radius bends the number of cross sections is greater than 3.

Fig. 3. Cross sections for stress analysis

1 - dummy node visible to user, 2 - automatically added nodes invisible to user

Toolbar Access

To insert a bend, select the desired node and use the menu option: Insert > Insert Bend

To view properties of an existing element: