Dimensioning

Isodraft can output several types of dimensions with different amounts of detail. The main types of dimensioning are:

• String dimensions (the default).

• Composite dimensions.

• Overall dimensions.

• Support dimensions.

The different types are illustrated in the Support, string and overall dimensions image.

String dimensions are measured between the following points:

• The start or end of a branch

• Changes of direction (bends and elbows)

• Component connection points (flanges, welds, screwed and compression joints, excluding gaskets)

Composite dimensioning ignores dimensions which the fabricator has no control over, particularly the sizes of individual components. Components which are directly connected to each other are therefore dimensioned as though they constitute a single composite item.

Overall dimensions indicate the lengths of the following sections of a pipeline:

• From the start of a branch to the first change of direction

• From each change of direction to the next

• From the last change of direction to the end of a Branch

• From the start of a falling section skew-box to the end of the falling section skew-box.

• Between Branch connections.

The user can specify:

• Whether or not overall dimensions cross Branch connections

• Dimensioning to Valve centrelines

The user can specify that overall dimensioning is to critical components. This can be used when the exact lengths of all components are not known at the time of design, for example, if the purchase of fittings has been delegated to a local fabricator. Critical dimensions are between points on assemblies of connected components. The points are chosen according to the first rule satisfied from the following list:

• Branch connection, such as Tee or OLET, but excluding tappings on PCOMs and Flanges.

• Change of direction, such as Elbow or Bend.

• Face of Flange or flanged component.

• Centreline of Instrument.

• Centreline of Valve.

• Origin of first component in assembly.

Single components in tube will be dimensioned to their origin; for example, Valves to their centreline.

Critical dimensions can be shown with or without component dimensions.

Support, string and overall dimensions

The DIMENSIONS command is used to set the dimensioning options. The default settings are:

• String dimensioning on (and, therefore, composite dimensioning off);

• Overall dimensioning off;

• Support dimensioning on;

• Valve centreline dimensioning off;

• Support/hanger dimensions shown alongside other pipeline dimensions.

Isometrics with no dimensions plotted can be produced.