Creo Routed Systems

Standardizing Spec-Driven Fittings, Part 3

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This is the final post of a three-part series covering the 13 different fitting codes defined by PTC in Spec-Driven Piping (for the first two posts see here and here, respectively). In this post, we will explore the INLINE_REDUCING,  CORNER_REDUCING, BRANCH_REDUCING, and BRANCH_LET codes.


PTC defines the typical BRANCH_LET as a weldolet (shown below). Unlike the two other branch fitting codes, BRANCH and BRANCH_REDUCING, a BRANCH_LET only has an inlet and outlet port. The only required parameters are FITTING_CODE, SIZE, and END_TYPE.

Weldolet in Creo

BRANCH_LET is unique in the orientation of the coordinate systems and insertion behavior. As the red rectangles indicate in the picture above, it is the only fitting type whose inlet and outlet coordinate systems have Z-axes pointing in the same direction, every other fitting code has them pointing in opposite directions.

The quirks of BRANCH_LET don’t end there; how they are inserted into a pipeline is also distinct. Unlike every other fitting type, they cannot be directly inserted into a pipeline. Shown below is an example of an initial pipeline (bottom pipe) and intersecting pipeline (top pipe) of different sizes. First, a “Break Point” must be inserted in the initial pipeline where it will meet the intersecting pipeline. Then the intersecting pipeline must be routed to the newly-created Break Point using the “To Pnt/Port” button. For standard weldolets, this should be done at a 90° angle.

Two Pipe Segments being joined for Weldolet Insertion

From there, you must use the “Insert Fitting” GUI on either of the initial pipeline sections – there are two sections now that we’ve added the Break Point. Select your weldolet fitting from the drop-down menus but be sure that the outlet size of the weldolet matches the size of the intersecting pipeline, Creo does not have self-checking logic for this insertion! If applied correctly, the new BRANCH_LET fitting will look similar to the picture below.

Final Weldolet Connection


PTC defines the typical CORNER_REDUCING as a reducing elbow and INLINE_REDUCING as a reducer. The behavior is nearly identical to that of the standard ELBOW (see here) and INLINE fitting codes defined back in our first post. The only addition is that both fitting codes must have a NEW_SIZE parameter on the outlet port to indicate that the size has changed since the inlet port. For the three REDUCING fitting codes, the NEW_SIZE can be either larger or smaller than the SIZE, not just smaller as “reducing” would indicate. An additional difference is that these two REDUCING fitting codes cannot support the FLOW_CONSTRAINED parameter due to the different sizes. Below is an example of an INLINE_REDUCING fitting also exhibiting Y_ECCENTRICITY (eccentric reducer).

Eccentric Reducer


PTC defines the typical BRANCH_REDUCING as a reducing tee. The behavior is similar to the standard BRANCH fitting (see here), but with some significant differences and limitations. BRANCH_REDUCING requires an additional parameter of BRANCH_SIZE located on the branch port and allows for optional Y_ECCENTRICITY and NEW_SIZE parameters.

It is first important to note that there is a documented bug with Creo that only allows for the branch port to be a different size and not the outlet port (see report here). In the text files (master catalog and spec), if SIZE=BSIZE≠NSIZE it will not let you physically insert that branch into the pipeline. If SIZE≠NSIZE≠BSIZE in the text files, it will allow you to insert the fitting into the pipeline but will ignore the value of the NSIZE and continue to use the SIZE value in outlet port for the pipeline (see this example in the text files and Creo behavior below).

Spec File Showing the BranchPipeline Split for Strange Branch



We hope you have enjoyed this series on the 13 fitting codes of Spec-Driven Piping. In our next post, we will be moving away from Piping (about time, right?) and diving into assembly management and the small but powerful differences in reference geometry features.