SB-111 C44300 tubes under external pressure

[Matrix_93]

Good evening,
I am checking exchanger tubes in SB-111 061 C44300 under internal and external pressure with ASME VIII div.1.
I have a internal design temperature of 100 °C and external design temperature of 185 °C.
In accordance with ASME IID note G6, the maximum temperature for external pressure not to exceed 175°C, Do we need to reduce external temperature because of this reason or we can do in other way?

Thank you

 

[Christine74]

Are you designing the exchanger for steam-out on the tube-side using 150# steam? From the design temperature you listed it looks that way.

I think your only options here are to:

1) Reduce your external design temperature

2) Select different a tube material. Pretty much anything that isn't brass would work.

3) If this exchanger isn't being designed for 150# steam-out, you might be able to design the tubes for a lower temperature, typically somewhere in between the shell-side design temperature and the tube-side design temperature. In order to do this you'd need to verify what the maximum metal temperature does not exceed the design temperature for all possible operating scenarios.


-Christine

 

[r6155]

See ASME VIII Div 1 UHX-19.2.1 Common Elements.

(b) Mean Metal Temperature Design. When common
elements such as tubes and tubesheets are designed for
a maximum mean metal design temperature that is less
than the maximum of the shell side and tube side design
temperatures, the heat exchanger shall be marked “Max
Mean Metal Temp” in addition to meeting all the requirements
of UG-19(a)(3) [see UG-116(j)].

Regards

 

[Matrix_93]

Thank you for your replies!
In my case my mean metal temperature for shell side is 90°C and maximum operating shell side temperature is 120 °C so I am far from 175 °C or 185 °C required by design condition and I have temperatures for design case only.
Unfortunately our client requires a verification with design temperatures, so I can't check tubes for differential pressure or mean metal temperatures only.
This material has been choosen by client and is ok up to 200°C before creep starts by ASME II D so I don't understand why external pressure is up to 175°C only for note G6 and for NFC-2 fig.
Is it mandatory to respect this note G6?

 

[SnTMan]

Matrix_93, you may not design for external pressure at a temperature higher than permitted by applicable Sec II, Part D Subpart 3 charts / tables. You would normally proceed by informing the client of the situation and then, with clients' permission, change material or design temperature. Note that design temperature may be limited for external pressure only.

Clients are often not aware of certain Code limitations.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand