Weld Pipe # 1500 WITH A FLANGE # 2500 NEED TRANSITION OR WELD DIRECTLY? 3

[brvs2014]

I have a pipe 6 "# 1500 but my Tien-in should do it on a # 2500 valve, the SCHD is the same for # 1500 and # 2500, you can either weld the flange directly to the pipe or I should relay transition by difference Thicknesses ??

 

[LittleInch]

I know it is sometimes done that way in piping schedules / specifications etc, but pipe is NOT rated by ASME class rating. It is designed by pressure containment, temperature, corrosion, material strength and other forces to a certain design code.

So yes, if the pipe is the same thickness as your ASME class 2500 flange / valve then you can weld it HOWEVER, the pressure rating of the system to which the class 2500 valve is welded to may not be the same maximum pressure rating as the flange / valve.

Now why you would want to use a higher pressure rated valve instead of a lower one is not clear.

It can be confusing in the long run to use higher rated flanges as then everyone thinks the entire system is good for class 2500 when it's not. Things like this get lost in the mists of time so mistakes can be made later.

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[brvs2014]

In the oil station there is a very old system of Water Rejection, due to its age the existing pipe is in very bad conditions, for this reason it has to be replaced, the old line to replace this designed with class # 2500, however to the Checking the pressure gauges on the HPS pumps shows that they work at 1200 psi, and because of this the # 2500 class would be over-designed since class # 1500 would be sufficient since its Design Pressure is in a range up to 3332 psi and class # 2500 has a design pressure range of 6160 psi, the class change would be given on an existing valve that is class # 2500

 

[LittleInch]

Design pressure really should come from the process engineers. It might be that the system now works at a much lower pressure than it was designed for, but that needs a change to the line list, P & IDs and a host of other documents. Be careful in just deciding to do this without proper review and approval.

By using thinner pipe or lower rated flanges you might be compromising the entire system downstream of this location.

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[KoachCSR]

LI is correct - the operating pressure and the design pressure of the system are two different things - while the pumps may be operating at 1,200 psi, they may have a shutoff head significantly higher - depending on the overpressure protection of the system, the piping you are looking to replace may see that full shut-off head. Be very leery in changing such a major aspect of the system without fully understanding the original design intent.

Also, LI is dead-on in his first post as well - my skin crawls a little when anyone refers to piping by ASME class rating. It's done, but it isn't correct - and leads people down wrong paths sometimes, IMO.

 

[brvs2014]

Thanks for your answers it is very good to hear different points of view, however I have several derivations of this line that are specified in # 1500. I attach a photograph.

 

[XL83NL]

What should the photograph tell us? I dont see any "Cl 1500" on there. The valve may be rated Class 1500 acc. e.g. B16.34, but one cant tell that from the picture.

 

[LittleInch]

Well looking at some of the other piping issues present in that photo I think a class 1500 flange is the last of your worries.... Someone clearly liked lateral connections. I've never seen it combined with a bend before now.

If there ever was one I doubt you have an up to date P&ID or line list to worry about.

How about what relief valves are there, trip settings etc?? I don't suppose this has gone through a MOC or HAZOP had it?

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Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Here's the photo for those who can't be bothered to download...

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

 

[blacksmith37]

Maybe I don't understand but it sounds like mixing API Wellhead with ASME piping ; two rather different sets of standards. Connecting API wellhead ( high strength steels ) to ASME( low or medium strength steels) was often a challenge . Usually a spool piece with one API flange and one ASME flange would be needed; often made in a shop where PWHT was well controlled.

 

[LittleInch]

That's a different subject but I found out recently that API 5000 flanges match ASME class 1500 and API 3000 flanges match ASME class 900. Pressure ratings ARE DIFFERENT (ASME is LOWER), but physically the flanges match.



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

 

[MickMc]

IMO if your system has been derated to Class 1500 you can use a Class 2500 Flange at the valve interface and pipe away from that with your Class 1500 rated piping components with wall thickness to suit your new design conditions.