socket weld pipe wall thickness 2

[dilodilo76]

I am aware that there is a matching pipe wall thickness for a given class of socket weld fitting (Sch80/XS pipe goes with a 3000# class socket weld fitting for example) My question is if that is a requirement in B31.3. In other words am I allowed to use, say Sch 160 pipe in a 3000# fitting? Or do I need to use a 6000# fitting if I use Sch160 pipe according to the B31.3 code?? I suppose this concept could apply to threaded fittings as well but I am more concerned with s.w. at present. Please help me out if you can.

 

[pennpiper]

The basic answer is , Yes you can use a thicker wall pipe with the 3000# fitting if you want to or need to and it has been done.
Example: Some Owner/Clients will specify that the first nipple off a header pipe for a vent, drain or pressure instrument shall be Sch 160 wall. This is to reduce the possibility of breakage caused by vibration indused metal fatigue.

This might also be done when maintence is in a pinch to get a system back on-stream and the Sch 160 pipe was/is all that is available at the time.

You need to be aware that the thicker wall will cause a "step" on the inside of the pipe thus creating a more turbulent flow.

Remember:
1. There is a rule for everything.
2. For every rule there will be an exception.

 

[dilodilo76]

Thank you for your input, it did seem logical but I wanted a second opinion. Now I have another question you would probably be able to help me with as well. What are the actual working pressures for forged fittings? ie 2000#, 3000# ,6000# & 9000#. I know this may sound stupid but I have been unclear on this for awhile. Is that the actual W.P. @ 100 deg F? If so one may end up using a lower rated fitting than if you did it by chossing based on the w.t. of pipe required. For example if say I needed to select a 1/2" S.W. fitting in a 300# ANSI class. The pipe I would require would be Sch160, so according to the forged fitting selection chart I have I should use a 6000# fitting to accomodate that wall thickness. But if I ovelook the w.t. matching the fitting thickness I should be able to use a 3000# fitting correct?

 

[MJCronin]

dilldo76..

Try ANSI B16.11

The methodology for matching the socket fitting clasification and the pipe schedule is contained within.

Generally speaking, for schedule 40 systems go with 3000lb fittings, schedule 80-6000lb fittings......when you get higher pressure systems, special rules apply.

This is, of course, the reason that piping engineers issue piping "class or line specifications"....which many owners immediately throw away.

-My opinion only

-MJC

 

[dilodilo76]

Yes, but what is one required to do when in the SAME piping system the pipe schedule increases, like 1" pipe needs S160 (supposed to use 6000# fittings) and 1-1/2" pipe calls for Sch80 (supposed to use 3000# fittings). Should the fitting rating jump to 6000# just because the pipe wall thickness went up or can I use 3000# accross the board if I don't care about the step in the wall thickness. And I am also still curious if the B31.3 allows this.

 

[pennpiper]

dilodilo,
Try this web site I think the table will answer most of your questions.

http://www.pennusa.com/pennpage/directory/forgecat/carbonsteel.html

 

[NozzleTwister]

Except in those cases where heavy wall pipe or nipples has been chosen for robustness, the pipe wall thickness required results from the design temperarture and pressure and corrosion allowance. Corrosion will be present in the fittings as well so when corrosion effects the required wall thickness I recomend to stick with the rules in matching the fitting class to the wall thickness.

NozzleTwister
Houston, Texas

 

[dilodilo76]

Good point. It does seem odd though that they would classify these fittings in such an abiguous term if that was to be considered though, wouldn't it. And if it was already considered you would think it would be a worst case consideration wich should eliminate me from even worrying about this. If that is true which does make sense then there should be a table/chart out there somewhere that shows what these fittings are good for under different design conditions including C.A. as well as stating which code/regulation the information was taken from. Any body have something like this.

 

[NozzleTwister]

The different temperature/pressure/corrosion allowance possibilties are endless.

They do provide a table, a simple one that covers all of the above, that couples the pipe bore to the fitting class.

Just like flange classes, corrosion allowance is taken care of by matching the flange bore to the pipe bore.

That's my opinion anyway....

NozzleTwister
Houston, Texas

 

[dilodilo76]

Another good point, look at it like flanges, match the schedule of pipe. The K.I.S.S. method. Do you have a link to that chart you referenced, and does it give reference to a specific code. I am just trying to find proof of this logical deduction, do you have a table linking the sch to the fitting rating and does it give any reference to the governing code? If so can I have a copy?

 

[pennpiper]

dilodilo76,
Try this website for flange data:

http://www.scsenergy.com/scsdataflgrating.htm

 

[NozzleTwister]

Refer to ASME B16.11-2001 (latest version), Section 2, Pressure Ratings. Specifacally look at paragraph 2.1.1, Basis of Rating and Table 2, Correlation of Fitting Class with Schedule Number...

ASME B31.3, ASME B31.1 and I think most piping codes recognize and list ASME B16.11 in their list of components accepted for pressure design.

These codes are copyrighted and not free. You can order from

http://catalog.asme.org/home.cfm?SEARCH=b16.11&SearchWithin=1

I found B16.11 has a 2005 edition out now.

Good luck

NozzleTwister
Houston, Texas