Pipe to pipe connection in branch tables

In branch tables for various piping classes with Pound rating from 150 to 2500 , how to decide the extent to which we can go for Pipe to Pipe connection (with or without reinforcement) what is the limitation for the pound rating

Regard's
Vaman-Arakeri

Arakeri,

There is no definitive, “must-always-apply” tenet or even a single rule of thumb; it depends on several issues which have to be considered on a case (specification) by case (specification) basis. Noteworthy issues being a) the design code which is being used, b) the type of material, c) the service conditions, flexibility and fatigue, d) preference of the designer, e) economics, f) the quality and competence of fabrication personnel, fitters and field technicians.

The prominent factor is the design code. Why? Because all piping design codes to varying degree provide their own slightly tailored recipes on how to address the other issues mentioned above. This after all is the whole purpose of design codes. B31.3 allows the ratio of welded branch diameter to header diameter to approach, but not exceed, 1. Thus all blocks in your branch chart at intersections of like sizes should naturally be a tee.

One commonly used rule of thumb is to nominate a forged, reducing tee for as many branch connections as your supplier commonly manufactures. This certainly is subject to the piping engineer analysing the marginal costs and doing a suitable economic trade-off. What you may find is that this only makes economic sense for the smaller header sizes. But using listed components has the convenience that they are pre-qualified and require no calculations.

Another practice is to use sockolets for all branches up to 50 NB for as many branches that, say, a manufacturer like Bonny Forge is likely to supply. Then all gaps may be subsequently filled in with welded branches – the decision as to whether reinforced or unreinforced being dependant on calculation and code. Incidentally, ASME B31.1 allows socket welded branch connections only for sizes less than 50 NB.

Practices already highlighted are all fit for purpose and safe. If multiple options pass the code test for any header / branch combination, the remaining differentiator is cost. For the case above where all gaps are filled in using welded braches, there is the possibility of then tweaking or refining some areas within that selection by changing to weldolets: in wrestling with the choice of a weldolet versus and reinforced branch, the weldolet is pre-qualified, requires no calculation and engineering pressure analysis, is easy to prepare and quick to fit, but it is honking chunk of a forging which you’re paying for. A welded branch, requires calculations to qualify it, additional inconvenience in cutting and preparing both pipe and pad for fabrication, but is cheaper in material cost.

For a piping material engineer to be comfortable with his branch chart configuration and given the assumption that any options are all safe and work, he must have the best marginal cost benefit across the entire chart. As an anecdote, I once knew of a piping engineer who had a branch chart excel spreadsheet, which was linked with a material and labour cost database for every type of branch for every pipe diameter. As one would then type in the symbol representing a class of connection on the chart block, a bottom line cost updated itself at the bottom of the page accordingly.

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