Standard BW, SW, Thrd Cross Fitting

[DGrayPPD]

New day, new question.

We are having an internal discussion about the use of standard piping crosses. One of my colleagues says crosses should not be used. Another colleague doesn't argue, but just states that he has seen standard butt weld crosses in the field, and another colleague says he doesn't understand why crosses cannot be used because they are a standard fitting.

The problem is that nobody can seem to give a definitive reason as to why piping cross fittings should or should not be used. I can admit, I personally have never had one in a design, nor do I recall seeing one in the field.

What are the reasons that piping crosses should not be used?
Is it a bad practice to incorporate crosses in designs?
Do crosses provide issues with streams coming together at the same location in the header rather than being offset and entering the header at different locations?
Is it better to weld two tees fitting to fitting instead of a cross? If so, why?

Thanks

 

[MFJewell]

It would depend on the desired hydraulics you want in the system. I personally have never seen them used in a real piping application. Using a cross, you will most likely get more flow going directly across the fitting than into the branches. If that is acceptable, I don't see why you couldn't use them. I'd have to model it to get a better idea of the hydraulic implications though.

 

[pennpiper]

Look here:

https://www.google.com/search?q=pip...s_snSAhXILSYKHWTTBKMQsAQIqwE&biw=1024&bih=633

Based on all these examples they are made. If they are made there must be a demand for them.

I have used them twice in the past. One was on a Urea Plant and the other was a Cumene Expansion Project in a very cold climate.
Both cases where I needed them I had one supply line splitting to three valved destination with a "minimum dead leg" requirement between the cross and the block valve on each branch.

Sometimes its possible to do all the right things and still get bad results

 

[rconner]

With proper design, I think crosses have along history of satisfactory use in the pipeline field. They are however (along with wyes etc) a potentially quite highly stressed configuration if made with metal of same or not much heavier wall than line pipe. In order to maintain full flow area, the "hoops" (that provide hoop strength for line pipe) are "broken" every which way in the midst of the cross.

 

[Gator]

pennpiper, was this in a 1-of-3 or 2-of-3 normally open (or normally closed) flow?

 

[pennpiper]

The Urea plant example was 2-of-3. The inlet Branch came from the surge tank. Branch 2, 3 & 4 went to the suction of three Positive Displacement Pumps, two on and one at rest on a regular cycle. The commodity was Urea slurry.

The Cumene plant example (I am not sure but) I think it was 1-of-3. The commodity was a hydrocarbon (Cumene) which would freeze at 40 degrees F with no flow.

Sometimes its possible to do all the right things and still get bad results