High temperature Inconel vessel design

[spmech]

1. I want to calculate the external pressure that can be applied to an Inconel 600(UNS No. N06600) pipe (3" NB, 40 sch/ 10 sch) at 1000C. The data in ASME code for Factor A and Factor B is given upto 1200F i.e. 650C. How do I compute this value at 1000C.
2. The yield strength and the ultimate tensile strength values for this material are given in ASME Section II, Sub part D only upto 900F. How do I extrapolate these values to 1000C i.e. 1832F?
Thanks in advance.

 

[metengr]

You don't. The F factor limiting values were based on test data that were submitted to the ASME Section II Code committee at the time these materials were reviewed and accepted for application.

If you need to determine actual ultimate tensile and yield strength values for this material beyond code recommended ranges, I would recommend you find a tech sheet on this material from Special Metals. They typically publish elevated temperature mechanical properties.

 

[Spiralis]

If you find the data for strength at 1000C, you can use the formula in ASME Sect II, Part D, Table 2-100(a) to determine design stress.

But read the rules carefully, to see if you can use this formula at tempreatures above 650C. The reason is that the material shifts form, and becomes very ductile at these temperatures.

 

[bvi]

Regarding buckling, you are well into the creep buckling regime and the curves in Section VIII are not applicable. They only consider elastic and elastic-plastic buckling. A method commenly used to evaulate creep buckling is in a paper by Don Griffen.

Regarding the basic allowable stress, at the temperature you are considering, creep properties will probably govern the allowable stress, so the tensile strength and yield strength probably will not factor into determining an allowable stress.

If this is B&PV Code, a Code Case would be required to do this. If it is B31.3 Piping Code, you have certain responsibilities outlined in the Code with respect to determining material suitability and the allowable stress per the Code stress criteria.

In short, you need some high temperature expertise to try to do this.

 

[spmech]

thanks to you all for the suggestions. dear metengr, i have got the tech sheet from special metals and working on it. however as Spiralis and bvi has already mentioned the problem goes to the creep buckling region where the material may not perform for our application and the pipe may require periodic change. i am thinking of using inconel 690. any suggestion?

 

[metengr]

spmech;
Actually, the Inconel 601 would be a better selection for pipe material terms of creep rate or creep deformation. At 1800 deg F, the stress to produce a creep rate of 0.001%/hr is slightly over 1 Ksi versus 0.8 Ksi for Inconel 690. The Inconel 690 was designed to provide improved corrosion resistance at elevated temperature.

If you review the elongation properties for this material, the elongation increases to almost 100% above 1300 deg F. What this means is that you will probably need to significantly increase the wall thickness of the pipe to compensate for the increase in elongation above 1300 deg F, and to keep the stress value well below 1,000 psi to assure a creep deformation rate of 0.001%/hr, and to avoid rupture under 10,000 hrs.

What is your application that would require the use of ASME B&PV code or ANSI Piping codes? If you are simply using the code or piping standards as a guideline for design, and are under no obligation from a Jurisdictional or Regulatory requirement, you have several different approaches to calculate allowable stress. I will caution you that this is not simple task, and should be performed by an organization that has expertise in elevated temperature stress analysis.

 

[unclesyd]

Adding to the above excellent posts there is one aspect of using Inconel at your temperature is that it is easily fluxed or will react with chemicals that would normally be immune to.

N2 is a bad actor and well as several of the Alkaline Earth metal compounds. Trace amounts of Boron compounds do a number on the metal.

 

[panduru]

folks! we seem to have lost sight of metengr's original observation - that once we bank on data from sources other than as given in ASME Code, then the rest of the design may not proceed on the ASME formulas and in fact, the design may not be considered to be conformant to ASME Code. In such a case, one may have to decide between confining to the code or designing entirely based on other sources. I did face this issue many times and had to fall back on other options where acceptable to the client. I would like to know if I am right at all.