Changing Direction – Axial Joint Deflection Explained

There are three ways to change a gasketed pipeline's direction:

1. Fitting (elbow, bend, etc.)
2. Curvature of the pipe barrel
3. Axial deflection at pipe joints

This tech brief focuses on the third method, axial deflection. Mathematically the idea is simple. For example, if you want to change direction by 5° and the allowable change in direction at each joint is 1°, then you need to deflect 5 joints.

The document explains this concept and the geometry involved. Click here to read.

Design Aid

There are two links in the tech brief -- the first is to a design aid. The designer initially inputs two variables:

1. Total angle to be turned
2. Allowable angle per joint (from the manufacturer of the pipe to be used)

The first output is the number of joints necessary. After adjusting the number of joints to a whole number, the designer then inputs a third variable: the distance between joints. Outputs are the offset at the end of the deflected pipe and the radius of curvature of the pipeline.

Offset Tables

The second link is to a series of tables that show the linear offsets from the original undeflected pipeline for different allowable angles.

This information should be helpful to a designer in deciding which method to use to curve a pipeline.

Regards,
	John F. Houle, P.E. Senior Technical Consultant, PVC Pipe Industry 201 E. John Carpenter Freeway, Suite 750 | Irving, TX 75062 T. 972.243.3902 | F. 972.243.3907 www.uni-bell.org