welded spec break issue 2

[cjabhijit]

WRT thread378-371363 need your feedback on this welded spec break issue.
We have HP Steam service shown with a spec break in between #900 to #300 Piping without any flanges. There is no material difference, both the line ids have CS.
HOWEVER, difference in between the thickness of joining pipes is 7mm. That makes me worry as I have no experience with these kind of welded spec breaks with such a thickness variation.
Pls share your experiences with this situation.

Thanks & Regards,
Abhijit

 

[BigInch]

Too much difference in wall thickness. The thicker wall should be taper bored to more closely match the thinner wall.

 

[pennpiper]

cjabhijit
Go here (#204A87]

http://www.wermac.org/documents/unequal_wallthickness.html

)and use the "Internal Offset - B"
Please note, the 30 degrees is the maximum recommended slope and the lesser angle 14 degrees is the minimum.

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

 

[LittleInch]

Soyn d's like the spec break is in the wrong place. Needs to be at a device which can effect a change in presure such as a valve or control valve

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cjabhijit]

Thank you all for your suggestions. There is one internal reservation on doing the welded spec break at valve asking us to avoid due to some hydro test requirements. It is a no flange piping. Valves to are welded as the #900 & spec is changing to #300. Again flanges are need to be avoided.
After lot of brain storming I am inclined to an idea which Big inch & Penpiper has mentioned a internally tapered transition piece to match the thicknesses of these 2 joining pipes with 7mm difference of thicknesses. It will add to one more weld but that would be okay I believe.

I am curious to know what could be the issues if we can just weld these together...I mean what issues you believe can happen?

Thanks all again.

Thanks & Regards,
Abhijit

 

[MickMc]

If you have welded valve which covers change in pressure which LI rightly points out the transition should be on the downstream of the valve weld and if you were to weld the 2 different wall thicknesses together you would probably be violating code and/or weld will fail examination as 7mm will not be within tolerances.

 

[BigInch]

It is entirely practical that a spec break be made at a valve, however there is no reason that it could not be made elsewhere, such as at the flange downstream of a 2xWE valve.

 

[LittleInch]

What design code are you using?

B 31.3 gives guidance on these sorts of issues in section 328.4.3

In a piping situation, welded spec breaks within a ruin of piping remain, IMHO, a bad idea.

It tends to mean one end of a bit of pipe has a higher rated flange than the other end, but with no clear break between the two pipes. On the outside one X" diameter pipe looks the same as another X" diameter pipe. I would be all to easy for someone to look at one end of the line and see say a class 900 flange and not realize the other end only has say a class 300 flange / wall thickness of pipe.

To me this is a much more serious issue than how to physically weld the two together.

A snapshot of the P&ID would be quite interesting....


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.