Class Break Flange

[davidysong]

Normally, there is one set of flange for class break, let says: different pressure, or different material....

Does anybody know what the reason is? Do we have to need this set of flange?

 

[BigInch]

If you can weld the materials together, then you can weld the class break.

you must get smarter than the software you're using.

 

[MJCronin]

I am not quite sure what question is being asked by the OP...

I believe that his question is " Why are flanges used at pipe class breaks?"

As I recall, there are only two ways to accomplish a piping class break: welded joint or set of flanges.

Where there is a change in materials, the flanged joint is always better because it avoids the welding/metalurgy problem associated with a dissimilar metal joint.

It is not possible in all circumstances to use flanges at these breaks. High Pressure Boilers, for example, commonly have dissimilar metal joints between the superheater and the steam feed piping

Where there is only a change in pressure class, I would question the PID. Pressure only changes in a system at a component (e.g. relief valve). The component should have the correct flange faces.

Anybody else ???

MJCronin
Sr. Process Engineer

 

[europipe]

Mostly the specbreak is at a flange weld after a valve with the highest conditions, not at a set of flanges,
Then you take the flangematerial what belongs to the connecting pipe.
Can You give us an example?

 

[BigInch]

In an all welded system, you cannot place any flanges, no matter where pressure drops happen to cross design class breaks.

MJC
In a long pipeline it is possible to have design pressure class changes not associated directly with valves or orifice flanges and other types of pressure reducing elements at particular points of a piping system. A long pipe is a pressure reducing element as well.

you must get smarter than the software you're using.

 

[LittleInch]

The reason - practicality and ease of installation. It also makes it mush easier to figure out 10 years down the line where the break is.

Pressure breaks are normally associated with a piece of equipment, normally a valve of some sort so it just makes it easy to weld to a flange a different spec pipe and then bolt it up.

Material change again is simply easier to manufacture and erect with flanges rather than welding in many instances.

I think BI meant to say wrt pipeline design pressure changes that these are mainly applicable for liquid lines due to elevation changes. Whilst Steady State flowing pressures do drop over distance, the shut in pressure can be much higher and this is what you need to design for. Thus the top of hill can never be as high a pressure as the bottom of a valley, but you just weld the pipes together without using flanges.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[davidysong]

thanks all for the comments.

somebody said: flange break is better for hydrotest. is it right?

 

[europipe]

What is a flange break?

 

[BigInch]

A broken flange!
"Class break", is typically a change in ANSI pressure "class" that is often made at a flange, because as well as being a physical item, a flange makes for an easily visible reference point as well. It normally marks a change in ANSI class ratings, ie ANSI#900/ANSI#600, but can also distinguish the point of any change of design pressures.

you must get smarter than the software you're using.