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#256 - 01/31/01 07:10 AM Material Selection
kberg Offline

Registered: 01/31/01
Posts: 1
Loc: Vancouver, BC, Canada
I am running an analysis of a piping system for a client with the following properties.

Fluid: Air
Code : B31.3

Inner Linning
Matl.: SB 409 UNS 08810 - 20GA
Temp : 1800 Deg.F

Outer Linning
Matl.: SA 240-304/304L Sch10S
Temp : <400 Deg.F

Air flows from a Ceramic Heat Exchanger through the pipe to a Tubine. The pipe section in question consists of a 6" Dia. inner pipe with some simple slip (lap) style joints, encased in about 2" of, refractory castable insulation, which in turn is encased in a 12" Dia. SA 240-304/304L Sch10S pipe. It appears that the inner linning will not restrain the piping due to the existance of several slip joints (I will confirm this and begin a new thread on modelling issues), and only the outer linner is the actual pipe which will be stressed. My questions are thus:

Assuming that the inner liner is simply for protection of the turbine from insulation particles.
1) Is the material SB409 UNS08810 acceptible in this application since it is listed in both ASME BPV Section I & VIII and B31.3 as "Plate, Sheet and strip"?
(I believe YES, as the liner will not restrain pipe movement.)

2) B31.3 Edition 1999 lists the maximum allowable stress as 1000psi at 1650 Deg.F. Apparently the BPV coe lists it as 500psi at 1800 Deg.F. May I still use this material as a piping liner eventhough B31.3 does not list stress values above 1650?
(I believe YES, as the liner will not restrain pipe movement.)

Assuming the inner liner restrains pipe movement.
1) Same question as above. (I believe NO)
2) Same question as above. (I believe NO)

Thanks for your time an input.
I look forward to your responses.
Kyle Berg

#257 - 02/23/01 04:03 AM Re: Material Selection
Sun Wee Offline

Registered: 12/20/99
Posts: 75
Loc: Calgary,Canada
Dear sir,

I think your material selection is O.K but it seems that Alloy 800H is costly design when inner liner do not undetake stress or load. However, the inner liner should be heat resistance material when liner is under stress,even if your system is not corrosive. Alloys 800H and 800HT have significantly higher creep and rupture strength than Alloy 800. The mechanical properties of Alloys 800H and 800HT, combined with their resistance to high-temperature corrosion, make these alloys exceptionally useful for many applications involving long-term exposed to elevated temperatures and corrosive atmospheres.

My answer to your question is as below ;

A. : Assuming inner liner is not fixed ;
1) I think 800H(UNS 08810) is applicable material for your piping system. However, If I were you, I would find alternative material,less expensive material such as Type 304H because I think, the inner liner is not a pressue containing part and not stressed part in this case. However, I am not sure if 304H is applicable in your system at 1800 oF.

2) Why not? This part do not undertake stresses !
ASME B31.3 indicates the use of unlisted materials and shows how to determine it's design stress. If you want to check stress,I think, you can use the design stress intensity from ASME VIII,Div.2 in lieu of ASME B31.3 hot allowable since B31.3 does not list the allowable value at 1800 oF. I think, this design stress intensity will be same the hot allowable stress got from ASME B31.3 Criteria. Strictly speaking, this may not be allowed in ASME B31.3.
I predict that 500 psi for Alloy 800H which you mentioned is the maximum allowable strength in tension from ASME VIII,Div.1 not Div.2.
You need to pay attention to get allowable value, that is, you have to understand that the allowable stress value are different for same material among various Codes with different Strength Criteria conceptions. For example; ASME B31.3 is hot allowable(for A106, 20ksi), but ASME VIII,Div.1 is Maximum Allowable Strength in Tension(for A106, 15ksi), and ASME VIII, Div.2 is Stress Intensity(for A106, 20ksi).

B : Assuming inner liner restrains pipe movement.
I would not like to consider this case since generally the role of inner pipe is to protect turbine casing or blade from the erosion or blistering(or other damage) due to the refractory particles.
I think, for this case, the liner design should be focused rather than material selection problem. Therefore; the inner liner should be specially designed to absorb liner movement. I have understand that the refractory material is casted on outer pipe with refractory anchor and ceramic fiber paper or other device is inserted between refractory material and liner.
It seems that if inner liner(Alloy 800H) have no special design to absorb axial thermal expansion, this piping may cause stress failue at joining part of two pipes. Of course, you can check these stresses due to differential themal expansion as typical jacketted piping system. Typical jaketted piping do not have significant differential thermal expansion between core and jacket pipe. It seems, however,that your system have too much thermal expansion aermal difference. Without special desgn,I cannot imagin any acceptable material to overtake the significantly high thermal stress like your sytem when the liner is fixed to outer pipe.

You indicate the cold wall temperature is 400oF and liner is 1800 oF with only 2ˇ± refractory thickness. Please advise if this 2ˇ±thickness refractory can drop 1200oF temperature. May I know that refractory material ? I do not have experience similar to your turbine system.

[This message has been edited by Soon Ryang, WEE (edited February 25, 2001).]
Sun Wee


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