Section 5: Design File Data in IDF Order

Section 5 of the HITS report contains a record of how the network is traversed as the intermediate data file is being generated. The software examines the network of piping and chooses the best

(that is, the one least likely to result in problems from ISOGEN) topo to begin the network traversal on. ISOGEN prefers certain navigation sequences over others and the interface software tries to choose the optimal sequence.

ISOGEN also requires that the traversal of the network be branch first order. This means that whenever a branch is encountered in the network, the traversal must head down the branch before continuing down the header.

To traverse the network in branch first order manner you start on the header topo and travel connect point by connect point until the value of branch is greater than 0 at some node.

When branch is positive then you jump down to the new topo and start traversing it until you come to another branch or to the end. If you encounter another branch then you must jump again to another topo. When the end of the topo is found then you return to the topo from which you jumped and continue tracing.

Example 6:

The following is an example of a network:

Name Occ cp# Node Topo Branch

PIPE 10 1 -1 1 0 1

In Example 6, topo 1 consists of a header, two pipes, and the run of a tee. Topo 2 consists of a branch, the branch leg of a tee and a branch pipe. Following the rules given above for traversal of the network would yield the following trace:

Name Occ cp in cp out Leg

Interpreting the HITS Report 6 - 23

Step 1 travels from one end of the first pipe to the other. Following the first pipe we travel into the tee. Notice that although the origins do not have node numbers they appear in the traversal whenever a change in direction occurs. This means that, for the tee, the traversal occurs from connect point 1 to the origin in step 2. At this point the branch flag is positive and so a jump occurs to topo 2. On topo 2 we travel from the origin of the tee to connect point 3 (which is the branch connect point) in step 3. In step 4 we travel down a pipe which is the last component on the topo. We then jump back to topo 1 and in step 5 travel from the tee origin to connect point 2. Finally, in the last step we traverse the remaining pipe on topo 1.

Refer to Figure 6-9 for an illustration of this traversal.

The header topo number can be found by examining the first line in the traversal. In this case the first line consists of PIPE — occurrence 10. Looking at the network description, observe that PIPE — occurrence 10 is on topo number 1. This makes topo 1 the header topo.

Figure 6-9. Traversal in Example 6

In ISOGEN terminology one step in the above trace is termed a component leg. Straight through components like pipe, flanges, and valves consist of one leg. Change of direction components like elbows, angle valves and so on consist of two legs. Branch components like tee’s, olets, 3-way and 4-way valves and crosses consist of three or four legs. In Example 9, the last leg of the tee is given a leg number of 4. By definition only 4-way components have a leg 3 (which would correspond to the 2nd branch leg).

Branches off from components formed by taps are termed branch legs and are not given a number. Branch legs are treated as other branches are though. When a tapped component is encountered in the network then all the tapped legs must be traced before continuing down the topo. Although olet type components have a different connect point skeleton than tee’s do they are treated similarly in the network trace. This is highlighted in the next example:

Example 7:

The following is a network:

Name Occ cp# Node Topo Branch

90E 8 1 -1 1 0 1

The network trace for this network is:

Name Occ cp in cp out leg

In Example 7, the first leg of the olet goes from connect point 1 to connect point 1. It is analogous to the step with the tee where traversal goes from connect point to the origin. In this case the traversal does not go anywhere and therefore is called a zero length leg. The second leg traverses from cp1 to cp2 — analogous to the previous example’s traversal from the tee origin to cp3. After the branch topo has been traversed we return to the olet for leg 4 which again goes from cp1 to cp1 — another zero length leg. This step is analogous to going from the origin to cp3 in the previous example.

Notice also the traversal through the elbow. Since the elbow causes a change of direction, it is traversed in two legs: 1) from cp1 to the origin and 2) from the origin to cp2.

Sometimes the traversal of the network requires traveling into the branch leg of a branch component. When this happens the leg numbers are assigned somewhat differently on the branch component.

Example 8:

The following is a partial network:

Name Occ cp# Node Topo Branch .

. .

PIPE 10 1 20 4 0 46

Interpreting the HITS Report 6 - 25

In Example 8, a lower numbered topo (topo 4) contains a back pointer to a higher numbered topo (topo 7). Whenever this happens, the traversal will enter branch.

The trace for this part of the network would be:

Name Occ cp in cp out leg

In this example, the branch leg of the tee is leg 1 since it is traversed first. Legs 2 and 4 are assigned arbitrarily in this situation and so tracing may go either way (ISOGEN has no preference). Refer to Figure 6-10 which shows this network traversal.

Figure 6-10. Network traversal in example 8

__________________________________________________________________________________________________________________________________________________