The global coordinate system in which the pipe model is defined is a right-handed orthogonal coordinate system, with the X-Y plane being horizontal and the Z-axis vertical upward.
The user is free to define the direction of the pipeline into this coordinate system, but it is practical to have the main pipeline axis more or less in the positive X-axis. And the main pipeline positive in the direction of the medium flow.
Local coordinate system (x-y-z)
The local pipe coordinate system is a right-handed, orthogonal system as well, with the x-axis in the direction of the pipe-axis, such that the x-coordinate increases with increasing pipe length. The y-axis is horizontal such, that the accompanying z-axis points in the positive Z-axis direction.
Or, for easy remembering: look (upstanding) into the positive x-axis and keep your left arm horizontal. That is the positive y-axis.
Where the y-axis intersects with the pipe wall, this is the origin of the angular measurement over the circumference. The direction of the angular measurement is right-handed as well around the x-axis.
All forces and stresses act on the advancing cut of the cross section. Thus, a positive axial force coincides with the positive x-axis and causes (positive) tensile stresses.
The local coordinate system turns with the turning pipeline axis, while the FLOCAL coordinate system is fixed to the original pipeline axis specified in Design Function 2.
Flocal coordinate system
The FLOCAL coordinate system is in fact the same as the LOCAL coordinate system, but is fixed to the original undisplaced pipeline axis.
Local coordinate system for joints
The local coordinate system for joints depends on the type of joint (see Direction of local X-axes for joints )
CoordinateSystems, last changed: 11/4/2020