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PED classification of branch pipes

PED classification of branch pipes

(OP)
Hi,

PED category for pipes (I-III, SEP) is selected based on medium, maximum allowable pressure and nominal size. Does there exist a consensus regarding where to draw the border between categories at branch-off pipes? For example a DN250 feedwater pipe with a DN50 branch off.

1. First possibility would be at the branch weld (the weld according to the bigger pipe, and the smaller pipe has its own category)
2. Second possibility would be at the first shut-off valve (category according to the DN250 pipe up to and including the valve)
3. Third possibility to categorize the whole connected pipe according to the bigger pipes category

The Guideline 2/28 (see link below, page 91) seem to suggest alternative 3, however i've seen examples of all three. Alternative 3 would in some cases lead to unreasonably high categories where two big systems are connected through a small pipes.

http://ec.europa.eu/enterprise/sectors/pressure-an...

Drex

RE: PED classification of branch pipes

Here's how I see it.

1) Every linenr makes a piece of piping unique, usually by means of an isometric. This is the crucial part in determining the PED classification. What we do at the company I work for, and have concensus with w/ our Notified Body, is that each linenr makes up 1 piece of pressure equipment.
2) In your isometric, determine the biggest DN size. Even if hypothetically, on your iso, the line is 45 meters long, has no branches, is DN 50 in main size (say for 44.8 mtrs), but has a local widening/reduction (e.g. for a thermowell) of DN 100, then the 'PED size' for classifying this isometric is DN 100. This a PED rule, I think elaborated in a guideline.
3) So when you have a branch, determine if you want to let it start with a new linenr or not. We usually make up a new linenr for each brand, unless its something like a small bypass, draint, vent or control valve manifold.
4) When youve made up all your linenrs, you now know to make up the PED classification of piping systems.


I guess it all boils down to how you uniquely identify your piping systems, hence unique drawings or pieces of pressure equipment.
AFAIK, there are no 'PED'-rules to determining when an isometric starts or stops.

Hope this helps.

PS: with a piping system I mean a set of pipe spools, that together make up 1 isometric. 1 Isometric may consist of several sheets. 1 isoemtric is 1 pressure equipment.
This is how we work, but I know lots of other companies who make a new isometric (hence linenr) for each flange break.

RE: PED classification of branch pipes

(OP)
Thanks for a great answer, maybe the best answer I have recieved in this forum. To me this is a new take on the issue and a great, clear way of defining it.

RE: PED classification of branch pipes

No probs. Im not known with your scope, so make sure to check this approach with your NoBo.
It would be a pitty if in the end it turns he does not agree on this approach.

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