Vertical Dummy Leg on Bends - CAESAR II - Reference Data

CAESAR II Applications Guide

PPMProduct
CAESAR II
PPMCategory_custom
Reference Data
Version_CAESAR
12

You can model dummy legs on bends in several ways. The three most common methods used to model dummy legs are outlined below.

Near/Far Point Method

  • Easy input

  • Dummy leg acts along centerline of vertical run

  • Dummy leg does not act at the proper place on the bend curvature

On Curvature Method

  • Easy input

  • Dummy leg acts at the proper place on the bend curvature

  • Dummy leg does not act along the centerline of the vertical run

Offset Element Method

  • Difficult input

  • Dummy leg acts at the proper place on the bend curvature

  • Dummy leg acts along centerline of vertical run

The element immediately after the bend must define the downstream side of the bend. Do not define dummy legs on the element immediately following a bend.

Dummy legs and/or any other elements attached to the bend curvature should be coded to the bend tangent intersection point. The length of the dummy leg is taken directly from the DX, DY, and DZ properties defined for the dummy leg of the pipe. There is no automatic alteration of the dummy leg length due to the difference between the bend tangent intersection point and the actual point on the bend curvature where the dummy leg acts. Enter the true length of the dummy leg in the DX, DY, and DZ boxes in the Classic Piping Input dialog box.

Input and output plots of the dummy leg always show it going to the bend tangent intersection point.

During error checking, the software generates a warning message for each dummy leg/bend model. Verify that the warning message description of the bend is accurate.

The bend shown on the left enters from the top left corner of the control station nodes 80 to 85 and exits horizontally to the right (nodes 85 to 90). The dummy leg is attached near the 45º point on the bend. The centerline of the dummy leg should line up with the centerline of the vertical run of pipe.

Coding the bend is the same for all three methods except alpha is not required for the Near/Far Point Method.

Dummy leg length is equal to the distance from its base to the bend tangent intersection point plus the bend radius.

  • Calculate α from the relation shown on the following page.

  • Enter α on the bend specification instead of the midpoint.

  • Calculate the offset distance y = R(1-sinα).

  • Add the distance y to the dummy leg length.

  • Calculate α and the offset distance x and y from the figure on the following page.

  • Add x and y to the dummy leg length.

  • Activate the offsets to subtract them from the dummy leg.