Dear all,

There in CAESAR2 only TGE/TD/12 code allow inputing +mill tolerance,for other codes,how to deal with it?There I met a power pipe,which inside diameter is 635mm,thickness is 31mm,temp. 545 degree and pressure 4.2MPa.The vendor can only guarantee the minimum inside diameter,for the wall thickness,the +mill tolerance is nearly up to 25%.The pipe have to be analyzed based on B31.1 code according the specification.I do not know how to model the pipe with this program.If I adopt the thickness of 31mm,what my concern is the 25% +mill tolerance maybe lead to some points overstress and some supports and equipment nozzle overload.If I do not adopt this thickness,what shall I do???
Any useful suggestion and guidance will be highly
appreciated!

Mr.Cheng,

One thing;
Where this 25% mill tolerance is from ? I would like to know this first and give my opinion.

Mill tolerance and corrosion allowance do not effect to force/moment calculation in the Caesar II but they are only considered in the code stress calculation as reduced section modulus or thickness terms.
The pipe in your system(540 C, I guess it must be steam in Power piping) will be the listed material in the ASME B31.1 to use the code allowable in Appendix Table-A. It would be 28", low alloy steel welded pipe(ASTM A691 or similar). For the most of welded pipes in the ASME B31.1/31.3 codes, the mill tolerance of wall thick. will be 0.3 mm which is from the plate mill(A387 or similar).
Your pipe material is an unlisted material in the Code ?

Sun

Mr. Sun,
Thanks for your reply.
The material is A335 P91,and the 25% +mill tolerance is provided by vendor.B31 codes do not address mill tolerance in flexibility analysis,which lead to more conservative result.Of course,all this is based on minus mill tolerance.But in this instance,the mill tolerance is plus,nonconservative result maybe produce if we ignore it.
This is my first time to handle pipes provided with inside diameters,and +mill tolerance must be considered to the wall thickness.
Hope for more response!

The IGE/TD/12 piping code is the only piping code that I am aware of that recognizes the +mill_tolerance condition.

25% does seem a little high, but if that's what your project specs call for, that's what you have to do.

Assuming your pipe fluid is a gas (i.e. density = 0.0), and you're only concerned about an increase in system weight, you can evaluate the +mill_tolerance condition by simply setting up an additional load case, and applying a mulitplier to the "W" component. For example, say you compute that the +mill_tolerance will increase the (pipe) weight of the system by 5%, then you could setup another load case like this:

case n) 1.05W + P1 + T1 (OPE)

Be careful with this multiplier on "W", it will increase all system weight - rigids, insulation, pipe, and fluid.

I think his concern is the effect the heavier than nominal wall thickness will have on the forces/moments imposed at the system termination points.

I would suggest making an additional run using a wall thickness of nominal + 25% to examine your potential heavier wall case for nozzle loads.

I think one of the reasons that we pretty much never consider an overtolerance case like this is that most manufacturers are going to work hard to avoid throwing away money like that by having a higher than required wall thickness. If anything, I would expect that the wall thickness that ends up in the field is a lot closer to nominal - 12.5% that we design for, since less material equals lower costs/higher profits for the manufacturer.

Kevin, what the matter? Cat got your tongue?

Commercial product for 28” size is welded pipe(EFW) but A335 is for seamless pipe. Mill tolerance for A335 is 12.5% max. in the ASTM.

Your pipe is probably specially ordered pipe with extra money. The best idea is to make separate runs as Edward suggested.

I assume;
-no C.A in your service
-no –mill tolerance from vendor

For the conservative analysis, I would model;
First file; Run with nominal wall thick.(i.e.31mm) with 12.5% mill tolerance and zero C.A in input fields.
Second file; Run with 25% heavier wall(i.e.38 mm, 711 O.D) with zero mill tolerance and 7mm C.A(38-31mm) to check stress at the thinnest section. This second run will get very conservative force/moment at the equipment nozzles.