Material high conditions 2

[jmoya]

Hi All,

I have designing a piping system in very high conditions. It´s a based water fluid and the conditions 350 bar (5076 psi) and 760ºC (1400 F). I am thinking in pipe B444 Alloy 625 (UNS N06625). The pipes that I need are 3/4", 1" and 1 1/2", but the thicknness obtained in the calculation are very high (I have to select Sch.XXS and we have many problems to find suppliers of this pipe).
What do think about that?
Do you recomended another material?

Thanks in advance.

 

[metengr]

jmoya;
What piping design code are you using for this high pressure and temperature system???

 

[jmoya]

metengr

I am using B31.3
Do you recomemded another one?

 

[metengr]

jmoya;
The design code is fine. At this service temeprature you will be limited in material selection to Ni-based alloys and wall thickness based on allowable stresses.

 

[MikeMet]

If you are having trouble finding a supplier of Alloy 625 you will have trouble finding a supplier for any high temperature alloys. For better high temperature strength, thinner wall, you can use Alloy 617. You also need to be careful using Alloy 625 for long period as 1400 deg. F due to secondary phase formation that produces hardening at room temperature, which may effect your start up procedures with regard to applying pressure/stress at low temperatures. Alloy 617 does not suffer from the same phenomena. Even better high temp strength needed, go with Alloy 718. Data can be found at SpecialMetals.com, Haynes.com, Rolledalloys.com

 

[jmoya]

metengr
So, do you think that Alloy 625 is not valid for this temperature?

 

[jmoya]

MikeMet,
Thank you for your information. I am searching the values of the "Basic Allowable Stresses" (S) in B31.3 tables for Alloy 617=N06617 and Alloy 718=N07718, but I don´t find it. Where I can find this data (at the temperature) to use in B31.3 calculation?
Thanks.

 

[metengr]

jmoya;
You have two options for using material not listed in Appendix A of B31.3. You can determine alowable stress by testing and methodes stated in B31.3 or you can use material listed in ASME B&PV Code, Section II, Part D. I would recommend you stick with material in Appendix A of B31.3.

 

[jmoya]

metengr,

If I use the values from ASME Sec. II PART D, Have I to apply some factor of safety? or I can use the listed values?

Thanks.

 

[metengr]

jmoya;
You can use the listed values in Section II Part D provided they are as conservative as B31.3 values in Appendix A. This is why I would remain with B31.3 endorsed materials.

 

[rolledalloy]

Alloy 718 requires an aging treatment to obtain high strength. At 1400F you are above the temperature at which it is commonly aged (double age treatment at 1325/1150F). We typically suggest it be limited to 1300F and below where its strength properties remain high. Also, 718 is easy enough to get in round bar, plate, and sheet. Piping is not very common off the floor.

You might want to look into Haynes 230 (UNS N06230). It might be covered by a code case (#2063) still rather than being in the tables, but has very high design stresses at 1400F and you would have a reasonable chance of getting pipe in it.